THE METABOLISM OF NMETHYLATED AMINO ACIDS II. THE COMPARATIVE AVAILABILITY OF I()TRYPTOPHANE, Z(f) AND dzaminonmonomethyltryptophane FOR GROWTH* BY WILLIAM G. GORDON (From the Department of Chemistry, Stanford University, California) (Received for publication, April 21, 1939) Synthetic aminonmonomethyltryptophane (dlcumethylaminop3indolylpropionic acid) was proved to be capable of stimulating growth in rats maintained on a diet deficient in tryptophane by Gordon and Jackson in 1935. However, the racemic Nmethylamino acid was found to be not as efficient as tryptophane itself for the promotion of growth. Two possible explanations for the relative inefficiency of the synthetic Nmethylamino acid were suggested: (1) The optical antipode of aminonmethyltryptophane of the same configuration as dtryptophane, the stereoisomer which does not occur in nature, cannot be broken down by the animal organism. (2) The aforementioned enantiomorph can be broken down but the conversion of dlaminonmethyltryptophane to tryptophane or to some physiologically available progenitor of the amino acid is not quantitative. In order to secure experimental evidence regarding the foregoing hypotheses a supply of either d or ZaminoNmethyltryptophane was required. With either of these substances at hand it would also be possible, in the event that ZaminoNmethyltryptophane alone were found to be growthpromoting, to determine whether the INmethylamino acid is equivalent physiologically to ltryptophane. * Aided by a grant from the Stanford University School of Medicine Research Fund. A preliminary report of this work was presented by title before the meeting of the American Society of Biological Chemists at Baltimore, March, 1938 (Proc. Am. Sot. Biol. Chem., J. Biol. Chem., 123, p. xliii (1938)). 309
310 NMethylated Amino Acids. II A convenient method for the preparation of Z(+)aminoNmethyltryptophane was made available as a result of the investigation of Hoshino in 1935 and that of Cahill and Jackson in 1938. Hoshino identified the crystalline substance, abrine, isolated from the seeds of Abrus precatorius (jequirity beans), as dextrorotatory aminonmethyltryptophane. Cahill and Jackson racemized abrine, proved that the racemic material was identical with the synthetic dlaminonmethyltryptophane of Gordon and Jackson (1935), and established the fact that dextrorotatory abrine is of the same optical configuration as the naturally occurring Z( )tryptophane. In the experiments to be described in the present report a comparison of the growthpromoting ability of Z( )tryptophane, E( +)aminonmethyltryptophane (I( +)abrine), and dlamino Nmethyltryptophane (dlabrine) has been made. EXPERIMENTAL The detailed procedures used for the preparation of Z(+) and dzabrine are described by Cahill and Jackson (1938). The I(+)abrine employed in the feeding experiments was isolated from jequirity beans. The compound was thrice recrystallized from hot water. Analysis of the purified material gave values of 12.72 and 12.80 per cent nitrogen; the calculated figure is 12.85 per cent. The specific rotation, [a]z5, of the Z(+)abrine was i45.7 in 0.5 N HCl. The dlabrine was obtained by racemization of I(+)abrine with barium hydroxide. The racemized product was recrystallized twice from hot 70 per cent ethyl alcohol. The nitrogen analyses in this case gave values of 12.69 and 12.66 per cent nitrogen. The purified material showed no optical activity. Young male rats were used as experimental animals in the growth studies. The animals were fed a complete diet until they had attained a weight of approximately 110 gm. They were then given a basal diet, deficient in tryptophane, which consisted of acidhydrolyzed casein 14.7, cystine 0.3, dextrin 37, sucrose 15, salt mixture (Osborne and Mendel, 1919) 4, ground agar 2, and lard 27 per cent. In addition each animal received daily 200 mg. of dried yeast and 100 mg. of cod liver oil, the vitamin supplements being administered apart from the remainder of the diet. The
W. G. Gordon 311 deficient ration was fed for a period of at least 35 days. The animals were then divided into five groups. Three rats in Group 1 served as negative control animals; they were maintained on the deficient diet throughout the investigation. Two rats in Group 2 were posit,ive control animals; following the initial depletion period they received the deficient diet supplemented with 267 mg. of Z(+)abrine per 100 gm. of basal food. In Group 3 two rats were fed the basal diet supplemented with 53.4 mg. of E(+)abrine per 100 gm. of food for 35 days; during the next 35 days the supplement was 50 mg. per cent of Z()tryptophane (53.4 mg. of I(+)abrine and 50 mg. of I( )tryptophane are equimolecular quantities). With two other rats in Group 3 this procedure was reversed; these animals received first the I()tryptophane and then the Z(+)abrine supplement. In Group 4 two rats were fed first 53.4 mg. per cent of I(+)abrine and then 53.4 mg. per cent of dlabrine as supplements; two other rats in bhis group received the supplemented diets in the reverse order. In Group 5 two rats received 106.8 mg. per cent of dlabrine for a period of 35 days followed by 53.4 mg. per cent I(+)abrine for a similar period. In all cases the amino acid supplements were incorporated in the basal, deficient ration. The diets were fed ad Zibitum. Individual food consumption data as well as weight changes were recorded. DISCUSSION The results of the growth studies are summarized in Table I. The rats in Group 1 lost weight slowly throughout the experiment on the unsupplemented diet. The positive control animals in Group 2 grew fairly rapidly when the deficient diet was supplemented with a substantial amount of Z(+)abrine. In Groups 3 and 4 the order in which the supplements were administered did not appear to influence the results. In Group 3 the four rats, during the period of Ztryptophane administration, grew at an average rate of 0.57 gm. per day. During the period in which an equimolecular quantity of I(+)abrine was fed, the same rats grew at an average rate of 0.32 gm. per day. These results indicate that Z(+)abrine is not quite as efficient as I()tryptophane in the promotion of growth and that the conversion of Z(f)abrine to tryptophane or to some physiologically available precursor of the amino acid is not quantitative.
312 NMethylated Amino Acids. II The four rats in Group 4 grew at an average rate of 0.43 gm. per day when the supplement was l(+)abrine, whereas the same rats, fed an identical amount of dlabrine, grew at an average rate of only 0.06 gm. per day. Furthermore, the two rats in TABLE Average Daily Weight Changes and Food Consumption of Male Rats Fed TryptophaneDejkient Diet and Various Supplements s ; 6 1 2 3 4 5 k 2 I 36 i 0.5: {6 70 I 0.z l102! 0.3: 75 l 35 i 0.5: 16 70 I 0.2( l105, 0.2t E l j4 53 0.2t 69 I i2.6 6: l 35, 0.6: 16 7a I t0.3: l105 I to.6t 6C I 35 1 0.5; 16 70 / i0.5: l105 I t0.2t 61 l 35, 0.6: 16 70 / i0.5; l105 I +o.ot l 35, 0.51 16 70 to.11 l105, t0.4t 7c l 43 0.5c L4 78 t0.3i 9113 l0.4: i gm. Qm. 4.4 3.5 3.4 4.0 3.2 3.0 3.8 5.9 4.2 4.4 5.5 3.7 4.5 4.2 3.9 4.1 4.2 3.6 3.7 4.0 3.9 3.7 4.3 72 I 35 36 70 7110: 4 I 53 0.06 2.8 54 69 j1.5 4.2 68 l 35 0.57 4.2 36 70 j0.31 4.0 71105 io.49 4.7 67 I 35 0.71 4.3 36 7Cl to.60 4.7 71105 io.34 4.8 65 l 35 0.63 4.0 36 70 to.31 3.9 71105 0.03 3.8 64 l 35 0.54 3.8 36 70 to.09 3.6 71105 to.37 3.9 71 l 43 0.49 4.0 44 78 to.46 3.9 79113 to.40 4.5 I Supplements per 100 gm. basal food I I 267 mg. I(+)abrine 53.4 mg. I(+)abrine 50 mg. Z( )tryptophane 50 mg. I( )tryptophane 53.4 mg. I(+)abrine 53.4 mg. l(+)abrine 53.4 dlabrine 53.4 mg. dlabrine 53.4 Z(+)abrine 106.8 mg. dlabrine 53.4 mg. I(+)abrine Group 5 grew at an average rate of 0.41 gm. per day during the period in which I(+)abrine was administered; when twice as much dlabrine was fed to the same animals, they grew at an average rate of 0.40 gm. per day. It might be concluded from these observations that d()abrine cannot be utilized by the rat
W. G. Gordon 313 for purposes of growth. However, the validity of this conclusion will depend ultimately on the results of studies with d()abrine itself. The results herein reported afford an adequate explanation for the relative inefficiency of synthetic dlaminonmethyltryptophane as a dietary substitute for tryptophane; for not only is the d( ) antipode unavailable to the rat for purposes of growth, but the I( +) compound is not equivalent physiologically to I( )tryptophane. The data also bring to mind t.he observations of du Vigneaud, Sealock, and Van Etten (1932) and those of Berg (1934) which proved that acetylltryptophane is capable of supporting the growth of rats maintained on a diet deficient in tryptophane and that acetyldtryptophane is ineffective in this respect. Thus, acetylltryptophane and I( +)abrine, both related configurationally to Itryptophane, are utilized in metabolism, whereas acetyldtryptophane and d( )abrine, possessing the configuration of dtryptophane, are not. Admittedly, this relationship is rather a loose one, as the metabolic paths followed by acetylltryptophane and I(+)abrine are undoubtedly different in the initial stages. In the case of the acetyl derivative the specificity of a hydrolyt.ic enzyme probably determines the physiological availability of the substance. On the other hand, utilization of the Nmethyl derivative doubtless depends on the specificity of a demethylating or deaminating enzyme. In two papers recently published Chin Kyusui (1938) has compared Z(+)abrine and Itryptophane with respect to the production of kynurenine and kynurenic acid in rabbits, the acceleration of hematopoiesis following phenylhydrazine hydrochloride administration in rabbits, and the promotion of growth in rats. For the first and last of t.hese physiological functions I(+)abrine was found to be somewhat less efficient than tryptophane, while its hematopoietic activity was stated to be equal to that of tryptophane. The results of the growth studies described by Chin Kyusui are thus in general agreement with those of the present investigation. SUMMARY A comparison of growth rates shows that Z( +)aminonmethyltryptophane (I(+)abrine) is well utilized by the rat but that it
314 XMethylated Amino Acids. II is not as efficient as tryptophane itself in the promotion of growth. dlaminonmethyltryptophane is considerably less efficient in this respect than the Z(+) compound and the tentative conclusion is drawn that the d() antipode cannot be utilized by the rat for purposes of growth. BIBLIOGRAPHY Berg, C. P., J. Biol. Chem., 104,373 (1934). Cahill, W. M., and Jackson, R. W., J. Biol. Chem., 126,29 (1938). Chin Kyusui, 2. physiol. Chem., 267, 12, 18 (1938). Gordon, W. G., and Jackson, R. W., J. Biol. Chew, 110, 151 (1935). Hoshino, T., Ann. Chem., 620, 31 (1935). Osborne, T. B., and Mendel, I,. B., J. Biol. Chem., 37, 572 (1919). du Vigneaud, V., Sealock, R. R., and Van Etten, C., J. Biol. Chem., 98, 565 (1932).