445 Pyrroles, Porphyrins and Related Com|>ounds 



Lactobacillus leichmannii they are required for the re- 

 duction of formate to the methyl group of thymine by a 

 pathway not involving methionine nor a hydroxymethyl 

 intermediate.^" In the same organism they have been 

 reported necessary for the synthesis of deoxyribose."*^ 



The isolation of actual coenzyme forms of cobamides 

 has permitted more precise determination of some func- 

 tions which are known to be direct. Barker and collab- 

 orators found that cell-free extracts of the anaerobe Clos- 

 tridium tetavomorphuin metabolized glutamate in a way 

 different from the citric acid cycle, catalyzing the equi- 

 librium : 



HOOC— CHo— CHo— CH— COOH ;=i HOOC— CH— CH— COOH 



I I I 



NH2 CH3 NH2 



Glutamic Acid /3-MethyIaspartic Acid 



HOOC— CH 



CH3— C— COOH 



Mesaconic Acid 



An orange form of pseudovitamin B12 was isolated and 

 found to be required for the first step.*® (It is noteworthy 

 that /jj-methylaspartic acid occurs in the polypeptide anti- 

 biotic, aspartocin.) The entire nature of this coenzyme 

 is still unknown, but the nucleotide base is known to be 

 adenine. Also a second mole of adenine nucleoside is 

 present, bound in such a way as to affect radically the 

 corphyrin spectrum, and cleavable by photolysis. The 

 nucleoside apparently is attached to cobalt, replacing the 

 cyano group. It contains an unusual sugar.*'' 



In this isomerization there are two possible migrating 



**' James L. Dinning, Barbara K. Allen, Ruth Young and Paul L. 

 Day, J. Biol. Chem. 233 674 (1958). 



■•" Mancourt Downing and B. S. Schwelgert, /. Biol. Chem. 220 521 

 (1956); W. T. Wong and B. S. Schwelgert, Proc. Soc. Exptl. Biol. 

 Med. 94 455 (1957). 



*s H. A. Barker, H. Welssbach and R. D. Smyth, Proc. Nat. Acad. 

 Sci. U. S. 44 1093 (1958). 



■*9 H. A. Barker, R. D. Smyth, H. Weissbach, J. I. Toohey, J. N. Ladd 

 and B. E. Volcanl, /. Biol. Chem. 235 480 (I960); H. Weissbach, 

 J. N. Ladd, B. E. Volcani, R. D. Smyth and H. A. Barker, ibid. 235 

 1462 (I960); J. N. Ladd, H. P. C. Hogenkamp and H. A. Barker, 

 Biochem.. and Biophys. Res. Comms. 2 143 (1960). 



