4900
AIIYOSHI IKAWA AND
/CONTRIBUTION F R O M
THE
ESMOND E.
Vol. 76
SNELL
BIOCHEMICAL INSTITUTE AND THE DEPARTMENT O F CHEMISTRY, UNIVERSITY O F TGXAS, A N D THE CLAYTON FOUNDATION FOR RESEARCH]
Oxidative Deamination of Amino Acids by Pyridoxal and Metal Salts1 B Y hfIYOSH1 IKd4WA\AND
ESXOND E. SNELL
RECEIVED MAY10, 1954 The oxidative deamination of pyridoxamine t o yield pyridoxal and "3, and of many a-amino acids to yield the corresponding or-keto acids and ammonia, is catalyzed in dilute aqueous solutions by pyridoxal and appropriate metal ions. 5-Desoxypyridoxal and 4-nitrosalicylaldehyde replace pyridoxal effectively, salicylaldehyde is far less effective. Of the metal ions tested, copper, cobalt, nickel and iron were effective; aluminum ions, which catalyze transamination reactions with pyridoxal, were ineffective in catalysis of these oxidative reactions. The evidence indicates that transamination is not an obligatory intermediate step in these oxidations. Of several amines other than pyridoxamine tested, only benzylamine was deaminated by this system. The biological significance, if any, of this chemical property of pyridoxal is not known.
Pfeiffer, et aLj2 have reported that in the substituted bis-salicylaldimine chelates formed from salicylaldehyde, Cu++ or Ni++, and amino acid esters, the latter component can undergo oxidative deamination in the presence, but not in the absence, of air. Martell and Calvin3 have suggested investigation of such systems as possible models of the enzymatic oxidation of amines. In previous studies of the reactions of aldehydes related to pyridoxal with amino acids, the oxidative deamination of glutamic acid by 4-nitrosalicylaldehyde and aluminum ions was noted.4 Oxygen was not required ; the hydrogen acceptor appeared to be the nitro group which was in part reduced completely to an amino group.* Because of the similarity in reactivity of pyridoxal and 4-nitrosalicylaldehyde toward amino a ~ i d s ,the ~ , ~ability of pyridoxal and metal salts to catalyze oxidative deamination of various amino acids and amines was determined. Results of such tests (Table I) showed that both pyridoxal and ai1 appropriate metal ion were required for the deamination of glycine and pyridoxanline. 0 1 the iiietnl ions tested, copper was triost effective, but iron, cobalt and nickel also wi-cw :wtive. Aluminum ions, which catalyze traiisaiiiiiiativii reactions between amino acids and were ineffective in catalyzing liberation of ammonia from glycine or pyridoxamine. Iroii was considerably less effective in alkaline than in acid solution, probably due to its observed precipitation from the alkaline solutions. It was not necessary to add the metal ion in its more highly oxidized state to effect these oxidations; however, this result is not definitive inasmuch as oxidation by air may have occurred to supply the metal ion in its higher valence state. 5-Desoxypyridoxal and 4-nitrosalicylaldehyde effectively replace pyridoxal in catalyzing deamination of pyridoxamine and glycine (Table 11). Salicylaldehyde did not promote deamination of pyridoxamine a t pH 4.0, and was much less active than the other aldehydes in deamination of glycine a t pH 9.6. The result again demonstrates the (1) .4 preliminary abstract has appeared ( h r Ikawa and E. E. Snell, Frrirv0lioir Proc., 13, 235 (19.5-1)). f?) 1'. l'fcitIer, M'. O B r r n i a n n a t i d 11. \i'ermcr, .I. j m i k l . C l r n ? . , 159 313 (1911). 13) .%,1,; 5 l a r t e l l and RI. C a l v i n , "Chemistry o f tile l I e t a l Chelate Coiiiixlnnds," l ' r r u t i c c - - F ~ ~ lIl m , . , Ktw Ycnk, S . Y,, 1!1:2? p . 309. 0:A I . I ~ : L W Y.$11
