Rowett Research Institute, Bucksburn, Aberdeen AB2 gsb

Transcription

1 Br. J. Nutr. (1978), 39, The similrity between lkline phosphtse (EC ) nd phytse (EC ) ctivities in rt intestine nd their importnce in phytteinduced zinc deficiency BY N. T. DAVIES AND A. A. FLETT Rowett Reserch Institute, Bucksburn, Aberdeen AB2 gsb (Received 13 April 1977 Accepted 2 July 1977) I. The ctivities of lkline phosphtse (EC 3. I. 3. I) nd phytse (EC 3. I. 3.8) were similrly distributed in the smll intestine of rts. Regionl differences in ctivity were reflected by similr differences in the cpcity of ligted intestinl segments to hydrolyse phytte in vivo. Activities were gretest in the duodenum nd lowest in the terminl ileum. 2. Specific ctivities of both enzymes were tenfold greter in the brush border frction of duodenl mucos compred with entire mucosl homogentes. 3. Brushborder lkline phosphtse nd phytse ctivities required both mgnesium nd zinc ions for mximl ctivity. 4. Zn deficiency induced by feeding diet low in Zn (.5 mg Zn/kg) cused similr reductions in ctivity of both enzymes. 5. Zn deficiency induced by feeding diets mrginlly dequte in Zn (12 mg/kg) nd phytte (1 g/kg) cused reductions in lkline phosphtse, phytse ctivities nd phytte hydrolysis in vivo. 6. It is suggested tht phytse ctivity is mnifesttion of lkline phosphtse nd the significnce of this in reltion to phytteinduced Zn deficiency is discussed. The nutritionl importnce of phytic cid (myoinositol hexphosphte) in limiting the vilbility of essentil dietry minerls clcium, zinc, mngnese, iron nd copper hs recently been emphsized (Dvies & Nightingle, I 975; Oberles, I 973). Few studies however, hve been mde on the metbolism of phytte by the intestinl mucos. Ptwrdhen (1937) demonstrted tht the mucos of rt intestine cn hydrolyse phytic cid with concomitnt relese of inorgnic phosphte, lbeit t very slow rte. Incubtion for up to 32 h ws employed before pprecible mounts of phosphte were relesed. The uthor ws unble to determine whether the hydrolysis ws ctlysed by specific phytse (myoinositol hexphosphte phosphohydrolse; EC 3. I.3.8) or by nonspecific phosphtses present in the mucos. Reinhold, Pscoe, Arslnin & Bitr (197) studying number of Zndependent enzymes in rt intestine, showed reltionship existed between the mucosl Zn content nd phytse ctivity lthough this ws not so close s tht between Zn content nd lkline phosphtse (EC 3. I.3. I). Intestinl mucosl lkline phosphtse ctivity is known to be Zndependent nd in the rt, Zn deficiency brings bout mrked reduction in enzyme ctivity (Willims, 1972). It hs been suggested tht phytse ctivity my be mnifesttion of lkline phosphtse (Pileggi, 1959) nd if so the bility of dietry phytte to ffect Zn vilbility my itself be influenced by the Zn sttus of the niml. The studies reported here were therefore conducted to determine first whether these two ctivities re expressions of the sme enzyme nd secondly whether Zn deficiency induced by dietry phytte could modify the metbolism of this compound by the intestinl mucos.

2 38 N. T. DAVIES AND A. A. FLETT MATERIALS AND METHODS Animls Mle Hooded Lister rts of the Rowett strin weighing between 12 nd 165 g were used in ll experiments. Diets In preliminry studies involving mesurement of phytse nd lkline phosphtse ctivities nd phytte metbolism by intestinl mucos in vivo, rts were mintined on commercil cube diet (Oxoid; H. E. Styles, Bewdley, Worcs.). In subsequent studies, in which the Zn sttus of the nimls ws modified, the bsl Zndeficient diet of Willims & Mills (197) ws used. This diet contined.5 mgzn/kg. When fed s Znsupplemented diet, ZnS,.7H2 ws dded to give Zn content of 5 mg Znlkg. When rts were given diets contining phytte, sodium phytte (Sigm Chemicl Co., St Louis, USA) ws dded to give phytte content of 1 g/kg nd the C content djusted by the ddition of CCO, to supply 13 g C/kg. The Zn contents of the diets were djusted by ddition of ZnSO,. 7Hz so tht they contined either.5 (unsupplemented), 12 or 1 mg Zn/kg. Mesitrement of phytse nd lkline phosphtse ctivities To enble direct comprisons to be mde between these two enzyme ctivities, stndrd conditions were employed with regrd to substrte concentrtion nd ph. Preliminry experiments showed the ph optimum for phytse ctivity ws between ph 7.2 nd 7.6 nd hence in ll experiments the ph ws mintined t ph 7.4. Since ech molecule of phytic cid contins six phosphte moieties, equivlence between Pglycerophosphte nd phytte ws mintined with respect to phosphte by using onesixth molr concentrtion of phytte compred with tht of Pglycerophosphte. Preprtion of tissue Smples of mucos from the duodenum (16 mm distl to the pyloric sphincter), jejunum (3248 mm distl to the pyloric sphincter) nd ileum (terminl 16 mm proximl to the ileocecl junction) were prepred by everting the pproprite segment nd scrping wy the mucos from the underlying muscle lyers with glss microscopeslide. The mucosl smples were homogenized seprtely in 5 vol..25 Msucrose (djusted to ph 74 by miniml volumes of TrisHC1 buffer) with ten strokes of Teflon pestle, glsstube homogenizer (concentrted homogente). For determintion of lkline phosphtse ctivity portion of these homogentes ws diluted in further 5 vol. 25 Msucrose (dilute homogente). Phytse ctivity Incubtions were crried out t 37 for 3 min in duplicte. Ech tube contined sodium phytte (.83 mm; equivlent to 5 mmphosphte) Trissuccinte buffer (5 mm; ph 74) nd mgnesium ions (.5 mm s MgCI2) in finl volume 3 ml. The inorgnic phosphte content of the substrte ws > I g phosphorus/kg sodium phytte nd t the concentrtions used in this ssy it ws below the level of detection by the method used for phosphte nlysis (Sumner, 1944). The rection ws strted by the ddition of.2 ml concentrted homogente. Preliminry experiments showed tht the rte of rection ws liner with respect to time for periods up to I h nd thus n incubtion period of 3 min ws therefore used in ll ssys. The rection ws terminted by the ddition of I ml trichlorocetic cid solution (2 g/l). After centrifuging, smple of the superntnt frction ws nlysed for

3 Gut enzymes nd phytteinduced Zn dejiciency 39 phosphte by the method of Sumner (1944). Regent blnks (no enzyme dded) nd enzyme blnks (no substrte dded) were subjected to the sme procedure nd the vlues obtined were subtrcted from the experimentl ssy vlues. Results were expressed s pmol phosphte liberted/mg protein per h. Alkline phosphtse A similr procedure to tht described for phytse ws employed except the tubes contined 5 mmbglycerophosphte insted of phytte, nd.2 ml dilute homogente, nd the rection ws crried out for only 15 min. This time ws chosen fter preliminry experiments hd shown the rection ws liner with respect to time for 3 min, fter which the rte declined. Results were corrected for regent nd enzyme blnk vlues nd expressed s phosphte liberted/mg protein per h. Protein concentrtion of the homogentes were mesured by the Biuret method (Miller, 1959) using bovine serum lbumin s stndrd. Phytse nd lkline phosphtse ctivity in mucosl brush borders Mucosl brushborder frctions of duodenl mucos were prepred by method similr to tht of Miller & Crne (1961). Briefly, the scrped mucos of the duodenl segment ws dispersed in 2 ml 5 mmedta which hd been djusted to ph 7.4 with Tris buffer nd ws then homogenized in topdrive blender (Mesurement nd Scientific Instruments Ltd, London SWI) t hlfspeed for I min. The homogente ws spun for 1 min t 85g in refrigerted centrifuge (MSE High Speed I 8 ; Mesuring nd Scientific Instruments Ltd). The pellet ws wshed by resuspension in 2 ml 5 mmedtatris buffer, homogenized second time nd centrifuged. The wshed pellet ws finlly resuspended in 2 ml.25 M sucrose (ph 74). Phytse nd lkline phosphtse ctivities were mesured on.2 nd.2 ml portions respectively using the sme incubtion condition s described for mucosl homogentes. When included, mgnesium ws dded s MgCI, nd Zn ions s ZnSO, (see p. 3 I I). Results were expressed s pmol phosphte liberted/mg protein per h fter corrections for enzyme nd regent blnks. Phytte hydrolysis in vivo The rte t which phytte ws metbolized by different regions of the rt intestine in vivo ws mesured using ligtedloop technique. Loops of either duodenum, jejunum or ileum (corresponding to the sme regions s described previously) were prepred s described by Dvies & Nightingle (1975). The loops were filled with I ml physiologicl sline (9 g NCl/l) contining 2 pmol sodium phytte, djusted to ph 7.4 with hydrochloric cid. After either 15 min (duodenum) or 3 rnin (jejunum nd ileum) the loops were excised, emptied nd the lumen flushed through with 5 vol. sline. Following protein precipittion with I ml trichlorocetic cid (2 g/l), duplicte portions of the superntnt frction were nlysed for phytte by the method of Holt (1955). The loss of phytte ws clculted by difference between the mount injected nd tht recovered nd the results expressed s pmol phytte/loop per h. Sttisticl tretment of results All comprisons were mde by Student s t test for unpired smples except in dietry studies in which Zndequte control rts were pirfed to Zndeficient rts when t test for pired smples ws used.

4 = 12.. c W 4 k 1. F I, 6. 4 m r Q m 4. E 2. v c 1... >. N. T. DAVIES AND A. A. FLETT t D J I D J I Fig. I. Regionl distribution of () lkline phosphtse (EC 3. I.3. I) nd, (6) phytse (EC 3. I.3.8) nd (c) phytte long the smll intestine of rts. Alkline phosphtse nd phytse ctivities (pmol phosphte libertedlmg protein per h) were mesured on intestinl homogentes, nd phytte loss from ligted loops of duodenum (D), jejunum (J) nd ileum (I). Results re men vlues of four rts with their stndrd errors ( x 2) represented by verticl brs. RESULTS Regionl distribution of phytse nd lkline phos9htse nd rte of loss of injected phytte It is well estblished tht lkline phosphtse ctivity is gretest in the proximl regions of the intestine nd is considerbly lower in the more distl regions (Moog, 1968). The results of mesurements of phytse nd lkline phosphtse ctivities in mucosl homogentes, prepred from different regions of the intestine re shown in Fig. I. It should be noted tht in ll regions studied, lkline phosphtse ctivity ws eight to ten times greter thn phytse ctivity. However, the profile of ctivities were similr, thus the ctivity rtio, ile1:jejunl: duodenl for lkline phosphtse ws I : 1.9 : 1.2 compred with I :22: 15.7 for phytse. Similrly the reltive rtes t which phytte ws lost from different regions of the intestine when injected into isolted loops in situ showed brodly similr distribution (Fig. I); the vlue for ilel: jejunl: duodenl ws 1 : I 7: 5.8. Locliztion of lkline phosphtse nd phytse in mucosl brush borders Hubscher, West & Brindley (I 965) showed tht most intestinl lkline phosphtse ctivity is present in the brushborder frction. This finding is supported by the present study where the specific ctivity of lkline phosphtse in the brushborder frction ws pproximtely ten times greter thn tht in the whole homogente (Tble I). Similrly the specific ctivity of phytse ws ten times greter in the brushborder frction thn of the whole homogente, indicting similr subcellulr distribution of these two ctivities s well s the sme regionl distribution long the length of the smll intestine. Ionic requirements of lkline phosphtse nd phytse Intestinl lkline phosphtse requires the presence of both Zn2+ nd Mg2+ for mximl ctivity. The effect of these two ions dded seprtely nd together on both lkline phos

5 Gut enzymes nd phytteinduced Zn dejciency 311 Tble I. Alkline phosphtse (EC 3. I.3. I) nd phytse (EC 3. I.3.8) ctivities pmol phosphte libertedlmg protein per h of duodenl homogentes nd duodenl isolted brushborder frctions of rts (Men vlues with their stndrd errors for four rts. Individul vlues were the verge of duplicte determintions for ech enzyme; both enzymes were ssyed in the sme homogente or brushborder preprtion. For detils of ssy, see p. 38) Alkline phosphtse Phytse Preprtion Men SE Men SE Homogente Brush border L Noions Mz+ Zn2+ M2++Zn2+ No ions M2+ Zn2+ M2++Znz+.5k~O.5 mm Both t.5 &M.5 mm ioth t.5 mm.5 mm Fig. 2. Duodenl brushborder lkline () phosphtse (EC 3. I,3, I) nd (b) phytse (EC 3. I. 3.8) ctivities (pmol phosphte liberted/mg protein per h) of rts t vrious concentrtions of mgnesium nd zinc ions. Results re men vlues for duplicte determintions of brushborder frctions prepred from two rts. phtse nd phytse ctivity in duodenl brushborder preprtion is shown in Fig. 2. Both enzymes exhibited lmost no ctivity in the bsence of both Zn2+ nd Mg2+. Slight ctivity ws present for both substrtes when Mg2+ lone ws present (.5 mm) nd considerbly greter ctivity ws found when Zn2+ lone ws present (.5 mm). However, the gretest ctivity towrds both substrtes ws when both ions were present together t concentrtion of.5 mm. The reltive increses in ctivities of both lkline phosphtse nd phytse due to these vrious dditions were very similr, gin indicting pronounced similrities between these two enzymes. It hs been reported tht lthough Zn is required for intestinl lkline phosphtse, the concentrtion required for mximl ctivity is firly criticl nd if n excess is dded n inhibition is observed (Willims, 1972). Accordingly studies were mde on the effects of different concentrtions of Zn2+ on the ctivities of lkline phosphtse nd phytse of the brushborder frction of duodenl mucos. The results re shown in Fig. 3. Incresing the Zn2+ concentrtion from.5 mm to.25 mm cused increses in both ctivities. However, no further increses were observed when the Zn2+ concentrtion exceeded.25 mm nd there ws n indiction tht t the highest concentrtion tested (I mm) there ws n inhibition of both ctivities.

6 312 N. T. DAVIES AND A. A. FLETT 7. c._ C i; 6. L ; F 5. m L $ 4. c 3. v % >._ I Zn concentrtion (mm) Fig. 3. The effects of different zinc ion concentrtions on lkline phosphtse (EC 3. I. 3. I) () nd phytse (EC 3. I.3.8) () ctivities (ymol phosphte liberted/mg protein per h) of duodenl mucosl brush borders of rts. ResuIts re men vlues for three rts. Eflect of Zn deficiency on duodenl lkline phosphtse nd phytse ctivity A mrked reduction in intestinl lkline phosphtse ctivity hs been reported to be n erly consequence of Zn deficiency in the rt (Willims, 1972; Leucke, Olmn & Bltzer, 1968). It ws therefore of interest to discover whether reduction of phytse ctivity prlleled chnges in lkline phosphtse when rts were fed Zndeficient diet. Young mle rts were trnsferred to Zndeficient diet (3 mg Zn/kg) or Znsupplemented diet contining 5 mg Zn/kg. Two groups of Znsupplemented control rts were used in this study; n d lib.fed nd pirfed group whose food intkes were mtched to those receiving the Zndeficient diet. After 4 d on these diets the rts receiving the Zndeficient diet suffered check in growth rte which ws ccompnied by decrese in food consumption followed by cyclic pttern of food intke chrcteristic of Zn deficiency in this species (see Willims & Mills, 197; Chesters & Will, 1973; Dvies & Nightingle, 1975). At 6 nd 14 d fter inititing these tretments duodenl mucosl homogentes were prepred nd ssyed for lkline phosphtse nd phytse ctivities. The results re shown in Tble 2. Clerly, Zn deficiency cused comprble reductions in the ctivities of these two enzymes for both tretment periods studied. In the rts killed on the sixth dy of tretment the lkline phosphtse nd phytse ctivities were reduced by 58 Yo nd 38 yo respectively nd on the fourteenth dy of tretment the ctivities were reduced by 72 yo nd 76% respectively. A comprison of the ctivities of the pirfed controls nd the controls fed d lib. mesured on the sixth dy of tretment showed no significnt difference for either enzyme indicting the reductions observed in the Zndeficient groups were direct consequence of the Zn deficiency nd not secondry to reduction in food consumption.

7 Gut enzymes nd phytteinduced Zn deficiency 313 Tble 2. The effect of Zn dejciency on lkline phosphtse (EC 3. I.3. I) nd phytse (EC 3. I.3.8) ctivity (pmol phosphte iibertedlmg protein per h) of' duodenl mucosl homogentes of rts (Men vlues with their stndrd errors for five rtsltretment. Individul vlues for ech rt were the verge of duplicte determintions for ech enzyme; both enzymes were ssyed in the sme homogentes) Alkline phosphtse Phytse Period on Dietry tretments diet (d) Men SE Men SE Zndeficient *.78 *13* Znsupplemented, ' pirfed' 6 15' Znsupplemented, d lib. 6 14'72 2.4~~ ~~ Zndeficient 14 3'6 o.45t.36 O W t Znsupplemented, ' pirfed' I NS, Vlues for Znsupplemented d lib. rts were not significntly different from those of pirfed Znsupplemented rts: P <.5. * Vlues for Zndeficient rts were sttisticlly significntly different from those of pirfed Znsupplemented rts: P.c '1. t Vlues for Zndeficient rts were sttisticlly significntly different from those of pirfed Znsupplemented rts: P <.1. The effect of dietry phytte on lkline phosphtse nd phytse ctivity of duodenl mucosl homogentes nd phytte metbolism in vivo A previous study from this lbortory showed tht when rts were given diet contining mrginllydequte Zn (15 mg Zn/kg) nd phytte (1 g/kg) they exhibited symptoms of Zn deficiency indistinguishble from those induced by feeding phyttefree, Zndeficient diet contining.5 mg Zn/kg. Studies were therefore crried out to determine whether under similr conditions ' phytse' nd lkline phosphtse ctivities would be reduced, due to ' phytteinduced' Zn deficiency nd, furthermore, if the bility of the intestine to metbolize phytte in vivo ws similrly ffected. Experiment I. In the first experiment rts were given diets contining 1 g phytte/kg. Zn ws dded to the diets to give contents of either 12 mg Zn/kg (Zndeficient) or IOO mg Zn/kg. This ltter concentrtion of Zn completely overcomes the deleterious effects on growth nd food intke induced by this level of dietry phytte (N. T. Dvies, unpublished observtions). The nimls receiving the diet contining the higher Zn content were pirfed to those receiving the Zndeficient diet. After 12 d on the diets, some rts from ech group were killed nd the duodenl mucos ssyed for lkline phosphtse nd ' phytse' ctivities. The remining rts were nesthetized nd the rte of loss of phytte from ligted duodenl loops ws mesured. The rts receiving the diet contining the lower Zn content exhibited reduced growth rtes ccompnied by reduced food consumption from the fifth dy of tretment indicting these rts were Zndeficient. Significnt reductions in lkline phosphtse nd ' phytse ' ctivities were observed in these rts compred with those receiving the diet contining the higher Zn content. Similrly, the rte t which injected phytte disppered from ligted duodenl loops in situ ws significntly reduced (Fig. 4). Experiment 2. In previous pper (Dvies & Nightingle, 1975) it ws shown tht feeding rts Zndeficient diet (.5 mg Zn/kg) contining 1 g phyttelkg cused fr more severe Zn deficiency thn tht induced by feeding the sme diet without dded phytte. The rts receiving phytte were in negtive Zn blnce nd suffered loss in bodyweight wheres those receiving the bsl Zndeficient diet just mintined bodyweight nd slight positive

8 314 N. T. DAVIES AND A. A. FLETT F. c. 5 c 9 2. Dietry Zn (mg/kg) 12 Dietry phytte (g/kg) z t *.5 1. I 1 m.e c L * f Fig. 4. The effect of phytteinduced Zn deficiency on () lkline phosphtse (EC 3. I. 3. I) nd (b) phytse (EC 3. I. 3.8) ctivities (pmol phosphte liberted/mg protein per h) nd (c) phytte loss (pmol/h) from ligted loops of duodenum of rts. Results re men vlues for five rts with their stndrd errors ( x 2) represented by verticl brs. Rts offered the diet contining 12 mg Zn/kg nd 1 g phytte/kg were fed d lib. for 12 d while those receiving the diet contining 1 mg Zn/kg nd log phytte/kg were 'pirfed' to those on the diet contining the lower Zn content. ** P <.1, *** P <.1 (piredr test). Dietry Zn (rng/kg) Dietry phytte (g/kg) *. f.5 1 f.5 i.5 (c) t f.5 Fig. 5. The effects of phytte inclusion in Zn deficient diet on () lkline phosphtse (EC 3. I.3. I) nd (b) phytse (EC ) ctivities (pmol phosphte liberted/mg protein per h) nd (c) phytte loss (pmol/h) from ligted loops of duodenum of rts. Results re men vlues for five rts, with their stndrd errors ( x 2) represented by verticl brs. Rts were offered the diets d lib. for 12 d. * P <.5, ** P <.1 (unpiredr test). 1 1

9 Gut enzymes nd phytteinduced Zn deficiency 315 Zn blnce. In view of these findings study ws mde of the effects of phytte inclusion in Zndeficient diet on lkline phosphtse, phytse nd phytte disppernce from ligted duodenl loops. The results of this experiment re shown in Fig. 5. Rts offered the Zndeficient diet dfib. for 12 d hd significntly lower duodenl lkline phosphtse nd phytse ctivities nd hd n impired bility to hydrolyse duodenlly injected phytte compred with those receiving the sme diet without dded phytte. These results my be interpreted s showing tht the more severe Zn deficiency induced by phytte resulted in greter reductions in lkline phosphtse nd phytse ctivities, which in turn resulted in the decrese in the rte t which phytte ws metbolized by the duodenl mucos in vivo. DISCUSSION Phytic cid is hexphosphte ester of inositol nd it would seem likely tht it my ct s substrte for lkline phosphtse since this enzyme brings bout the hydrolysis of orgnic phosphte esters. The results of the present study fully support this hypothesis since under ll conditions studied phytse ctivity prlleled lkline phosphtse ctivity. Thus the regionl distribution of these two phosphtses long the intestine, their ionic requirements, inhibition by excess Zn2+ dded in vitro nd subcellulr locliztion were qulittively similr. In greement with the findings of Willims (I 972) nd Leucke et i. (I 968), intestinl lkline phosphtse ctivity ws reduced in Zndeficient rts compred with either pirfed Zndequte controls or controls fed d lib. nd, similrly, phyttehydrolysing ctivity of the sme homogentes ws reduced. In view of these findings we support the proposls of Pileggi (1959) nd Mddih, Kurnick, Hulett & Reid (1969) tht intestinl phytse ctivity my be mnifesttion of lkline phosphtse ctivity. A similr conclusion ws reched by Dvies, Ritcey & Motzok (197) nd Dvies & Motzok (1972) who conducted similr series of studies on chick intestine. In greement with the present study on the rt, Zn deficiency reduced the ctivities of both phosphtses in the chick nd, in ddition, when extrcts of the mucos were subjected to gelfiltrtion chromtogrphy, the two enzymes showed brodly similr ctivity profiles. This view hs been chllenged by Bitr & Reinhold (I 972) who showed some divergence of ctivities during fourstge prtil purifiction of lkline phosphtse of duodenl mucos from rt, chicken nd cow. Similrly, prtil seprtion of phytse nd lkline phosphtse ctivities of chicken mucos were obtined when mucosl extrcts were chromtogrphed on DEAEcellulose. However, most ctivity for both enzymes resolved into two overlpping zones. Alkline phosphtse ctivity of the intestine is not due to single enzyme but to number of isoenzymes which re chrcterized by n bility to hydrolyse phosphteester linkges t ph vlues greter thn 7. Their substrte specificities nd ph optim for pglycerophosphte or pnitrophenol phosphte differ mrkedly (reviewed by Moog, I 968) nd it would seem likely, therefore, tht t lest some of the isoenzymes which contribute to lkline phosphtse ctivity my function to greter or lesser extent s phytses. The results of experiments in which rte of loss of injected phytte from ligted intestinl loops ws mesured indicte tht this spect of intestinl ctivity prllels phytse distribution long the intestine nd both of these ctivities re reduced to comprble extents when rts suffer different extents of Zn deficiency induced by dietry phytte. Since phytic cid is not bsorbed (Oberles, 1975) it seems likely tht the loss of injected phytte represents hydrolysis in vivo of phytte in contct with lkline phosphtse of mucosl brushborder membrnes. A role for phytic cid in reducing Zn vilbility hs been well estblished since ODell & Svge (1957) first showed tht Zn in some plnt proteins ws poorly vilble compred

10 3 16 N. T. DAVIES AND A. A. FLETT with the Zn in protein of niml origin. Although phytte hs been shown similrly to reduce the vilbility of number of essentil divlent metls, i.e. Fe (Widdowson & McCnce, I942), Cu, Mn (Dvies & Nightingle, 1975), Mg (Seelig, 1964) nd C (Bruce & Cllow, 1934), our present findings highlight how its effects on Zn nutrition my be of greter significnce. This study shows tht the metbolism of phytte both in vitro nd in vivo depends upon n dequte supply of dietry Zn. Thus if the dietry Zn intke is mrginl nd the diet contins phytte the reduction in vilbility of Zn cn led to Zn deficiency stte which in turn decreses the bility of the intestinl mucos to hydrolyse phytte. One cn postulte tht the lowered bility of the intestine to metbolize dietry phytte would result in n incresed concentrtion of phytte in the intestinl contents which in turn could bind more Zn nd further reduce dietry Zn vilbility. In conclusion, the results of this current study gin emphsize the importnce of dietry phytte in reltion to Zn nutrition. If mn increses his dietry supply of protein from cerel nd soybsed products, both of which re rich in phytte, due regrd must be pid to the effect this my hve on the supply of dequte mounts of Zn in n vilble form. REFERENCES Bitr, K. & Reinhold, J. G. (1972). Biochim. biophys. Act 268,442. Bruce, H. M. & Cllow, R. K. (1934). Biochem. J. 28, 517. Chesters, J. K. & Will, M. (1973). Br. J. Nutr. 3, 555. Dvies, M. & Motzok, I. (1972). Comp. Biochem. Physiol. 42, 345. Dvies, M., Ritcey, G. M. & Motzok, I. (197). Poult. Sci. 49, 128. Dvies, N. T. & Nightingle, R. (1975). Br. J. Nutr. 3, 243. Holt, R. (1955). J. Sci. Fd Agric. 6, 136. Hubscher, G., West, G. R. & Brindley, D. N. (1965). Biochem. J. 97, 629. Leucke, R. W., Olmn, M. E. & Bltzer, B. V. (1968). J. Nutr. 94, 344. Mddih, V. T., Kurnick, A. A., Hulett, B. J. & Reid, B. L. (1969). Proc. SOC. exp. Biol. Med. 115, 154. Miller, D. & Crne, R. K. (1961). Biochim. biophys. Act 52, 293. Miller, G. L. (1959). Anlyt. Chem. 31, 964. Moog, F. (1968). In Hndbook of Physiology: Alimentry Cnl vol. 3. Intestinl bsorption. Wshington, DC: Americn Physiologicl Society. Oberles, D. (1973). Toxicnt Occurring Nturlly in Foods, p Wshington, DC: Ntionl Acdemy of Sciences. Oberles, D. (1975). In Proceedings Western Hemisphere Nutrition Congress ZV p. 156 [P. L. White nd N. Selvey, editors]. Acton, Msschusetts: Publishing Sciences Group, Inc. O Dell, B. L. & Svge, J. E. (1957). Fedn Proc. Fedn Am. Socs. exp. Biol. 16, 394. Ptwrdhen, V. N. (1937). Biochem. J Pileggi, V. J. (1959). Archs. Biochem. Biophys. 3, I. Reinhold, J. G., Pscoe, E., Arslnin, M. & Bitr, K. f 197). Biochim. biophys. Act 215,43. Seelig, M. S. (1964). Am. J. clin. Nutr. 14, 342. Sumner, J. B. (1944). Science, N. Y. 16, 413. Widdowson, E. M. & McCnce, R. A. (1942). Lncet i, 588. Willims, R. B. (1972). Br. J. Nutr. 27, 121. Willims, R. B. & Mills, C. F. (197). Br. J. Nutr. 24, 989. Printed in Gret Britin