- -N - ! I-' ~,...;... t.~ii1]~ ..~ -; ~~ ~ ~ ~::;;~~u~ 0.. 'i.,2. 2 Fatty Acids. - d-i- I I - -N ,..., ]. -:$ :;! I~ ~ 6. e~~~o:: ~ ~.

Transcription

1 2 Rajenra Prasa Structure an Distributin f Membrane Lipis : ]..;: :u -:$.;.g :=., -3., e : e u "'" 's ;:1,.; :;! Q., e fc l!.,., " "'" :e.! -' 5 Q (; i> i:i: <) ;::;., - -i- - '" ; &n N MM \O\)'Q:;":!: '" MO"lt'OOOOO NNN -, 0 ::e -; -:::0 3-::: 1:!,0 e:- ':: :; 0'" C$ Ll e,, ';::: e e::., c c s '& C)..!!'S: t e -5 cu.- V)';:'= fr! ::::0(1) >- V)"'CSg g"u. Q.c. C4:::8:0 := '-'- :: 0.<>.i;->-s8 <>::s0, -::;;::;;Zl-'<)>-u,,:: ::;;u \O., -N"")cr)r N N :::\O"\Ot--. NM "'0 00 -N- 00.,., M - -N - '" "")MM"'tf')O \D«\cO 00 :2;:g:g:g ::;;::ll 'i.,2 t.i -0."0 cu g-., u. :a cf'a.tj:9 ::, s.5":;: ':E.:E--::":: :6 :g f::! ':! :g :g ':: c:s 0 Ct CG Ct Ct Q.,Ct t.ii1] c:c Q.,.::::::'-:: '?,.;. 2 Fatty Acis All sapnifiable lipis cntain fatty acis as builing blcks; hwever, nly traces f fatty acis are present in free frm in tissues an cells. Fatty acis are carbxylicacis with hyrcarbn chain an a terminal carbxylgrup. The hyrcarbn chain may cntain ne (mnenic r mnunsaturate) r mre than ne (plyenicr plyunsaturate) ublebn. n certain instances, fatty acis cul be cyclic an branche. Table 2 lists sme f the cmmnly ccurring fatty acis. While ver 100 types f fatty acis exist in nature, palmitic aci (C16:0)'stearic aci (C'8:0)amng saturate an leic aci (C'8:') amng unsaturate are mst cmmn. n mst f the fatty acis f higher rganism, the first uble bn is between carbn atms 9 an 10. n plyunsaturate fatty acis, ne uble bn is between carbn atms 9 an 10,while ther uble bns usually ccur betweenthe 9, 10 uble bn an the methyl terminal en f the chain. The cnfiguratinf ublebn is mstlycis-,whichprvies a rigi kink f 300 in the hyrcarbn chain, whereas the trans- cnfiguratin results in an extene chain structure (Fig. 1). The fatty acis iffer frm each ther with respect t their hyrcarbn chain length (C,-C36)' an egree f un saturatin (number f uble bns) which als gvern their physical prperties an f the cmpun that cntains them. The melting pint f fatty acis is strngly influence by the length an egree f unsaturatin (Table 2). The fllwing sectin very briefly escribes sme f the cmmn sapnifiable membrane lipis. Amng nnsapnifiable lipis nly sterls are mentine. Figure 2 shws varius builing blcks f sme f the membrane lipis (sapnifiable) which are briefly iscusse in the fllwing sectin.

2 Table 2. Sme cmmn fatty acis Trivial name Systematic name Saturate. straight chain fatty acis General frmula: CH,(CH,).COOH Capric aci n-decanic aci Lauric aci n-decanic aci Myristic aci n-tetraecanic aci Palmitic aci n-hexaecanic aci Stearic aci n-octaecanic aci Arachiic aci n-eicsanic aci Behenic aci n-dcsanic aci Lignceric aci n-tetracsanic aci Certic aci n-hexacsanic aci Unsaturate fatty acis Palmitleic aci cis-9-hexaecenic aci Oleic aci cis-9-0ctaecenic aci Vaccenic aci cis-l-octaecenic aci Linleic aci cis,cis ctaecaienic aci a-linlenic aci Arachinic aci All-cis-9,12,15- ctaecatrienic aci Al-cis-S,8.11,14-eicsatetraenic a mp' Carbn Structure skeletn 10:0 CH,(CH,),COOH :0 CH,(CH,J,.COOH :0 CH,(CHJ"COOH :0 CH,(CH,)"COOH :0 CH,(CH,)"COOH :0 CH,(CH')8COOH 22:0 CH,(CH,)COOH :0 CH,(CH,J"COOH 26:0 CH,(CH,J"COOH :1" CH,(CH,J,CH =CH(CH,),-COOH :1" CH,(CH,),CH =CH(CH,),-COOH 18:141' CH,(CH,J,CH =CH(CH,),-COOH :2"." CH,(CH,),CH =CHCH,CH =CH :3 -CH(CH,J,COOH CH,CH,CH =CHCH,CH =CHCH,- -CH =CH(CH,J,COOH :44M CH,(CH,),CH = CHCH,CH = CH- H,CH '7 q(<;:h,),cooh. -a ::r 1ft '0 ::s- O e -< n) a: ) 1ft '\ '\ '\ f i

3 6 Rajenra Prasa Structure an Distributin f Membrane Lipis 7 LYCERlDES MEMBRANE LPDS SPUNGOLPDS CH20H HO-2C-H 3CH20-P-OH OH CH2-O-C-R R'.C-O}C-H 3CH-O-P-OH 2 OH 'YACD YAClD J-l ALCOHOL Fig. 2. Builing blcks f phsphglyceries an glyclipis L-glycerl-3-phsphric aci L-phsphatiic aci Fig. 3. L-glycerl-3-phsphric aci is the ismer f glycerl phsphate fun in natural phsphglyceries an belngs t the L-sterechemical series. L-phsphatiic aci has tw fatty acis, Ran R', esterifie t the hyrxyl grups at carbn atms 1 an 2. The parent cmpun f the series is thus the phsphric ester f glycerl tw are esterifie t fatty acis. The resulting cmpun phsphatiic aci (PA) is cmmn t all phsphglyceries (Fig. 3). PA es nt cntain any plar hea grup (X). Althugh it nrmally exists in small amunts, it is very imprtant as a bisynthetic intermeiate f phsphglyceries. Phsphglyceries iffer frm each ther with respect t plar hea grups (X) whse hyrxyl grup is esterifie t phsphric aci (Fig. 4). Since phsphglyceries cntain a plar hea grup an tw nn-plar hyrphbic chains f fatty acis, they are amphipathic in nature. The mlecule f a phsphglycerie r, fr that matter, f any ther phsphlipi can be visualise as having a istinct plar an a nn-plar main (Fig. 4), while phsphglyceries are sluble in mst plar rganic slvents, they are insluble in acetne. Figure 5 epicts ifferent plar hea grups (X) f cmmn phsphglyceries. Phsphatiylchline Phsphatiylchline (PC) is the mst abunant phsphglycerie in animals an ften in higher plants an yeasts. t cntains chline as a hea grup esterifie t phsphric aci (Fig. 5). The cmplete hyrlysis f PC wul thus yiel tw mlecules f fatty acis an ne mlecule each f glycerl, phsphric aci an chline. A lys-erivative f PC, where nly ne f the tw available hyrxyl grups is esterifie t a fatty aci, als exists in tissues, albeit in small amunts. Phsphatiylethanlamine Phsphatiylethanlamine (PE) is generally the secn mst abunant phsphglycerie f eukarytic cells an ccurs as a

4 x - p-- H-sCH. Plar Dmain Fig. 4. Structure f phsphatiic aci. When esterifie t X (an alchl), it represents the general struture f phsphglyceries. The structure als emphasises the amphipathic nature f phsphgylceries Chline Structurean Distributinf MembraneLipis 9 FORMULA PHOSPHOGLYCE Phsphatiylchline Ethanlamine Phsphatiylethanl (PE) Serine Phsphatiylserine( = :H ;H ;H. H. H. H. H. H. H. Nn-plar Dmain nsitl -{ _yfuw.rj Glycerl Phsphatiylg1ycer COB Phsphatiyl- U-ar. 0 glycerl -r:1 ca.& kl Diphsphatiylgly (DPG) Fig. 5. Hea grups f majr phsphglyceries majr phsphlipi f bacteria. The cmplete hyrlysis fpe yiels ne mlecule each f ethanlamine, glycerl, phsphric aci an tw mlecules f fatty acis (Fig. 5). The lyserivative f PE is rarely fun in animal an plant tissues.

5 <;;P!e,r\:1S,r;t r,!) D,iitibPliql1',f :Membrane,t, 'j" Llpls i ":.' i.yh,; RAJENDRA PRASAD 1 Backgrun This chapter briefly presents sme basic infrmatin n the structure an prperties f membrane lipis. Sincesuch infrmatin is alreay available in numerus bichemistry text bks (Jain 1988; Zubay 1988; Lehninger et al. 1993), etaile iscussin is avie. This chapter prvies reay reference t varius cmmn membrane lipis whse separatin an ientificatin is escribe in this manual. Typically, mst f the lipis f an rganism are fun preminantly in membranes. Only a small amunt f it is fun elsewhere in cells. Table 1 epicts lipi cmpsitin f ifferent membrane preparatins. The ata f Table 1 give sme iea abut variatins an peculiarities f lipi cmpsitin f ifferent membranes. Fr iscussin, lipis can be classifie int tw majr classes: sapnifiable (which cntain fatty acis which frm saps, i.e. salts f fatty acis n alkaline hyrlysis) an nnsapnifiable lipis (which nt cntain fatty acis). The sapnifiable lipis iffer in their backbne structure, t which fatty acis' are cvalently attache. Structure an nmenclature f fatty acis are intruce befre the ifferent classes f lipis which cntain them, are escribe. Schl f Life Sciences, Jawaharlal Nehru University, New Delhi-ll0067, nia