AMINO-ACID CATABOLISM 25 



Furthermore, Binkley's dialysed cell-free preparation of 

 serine deaminase was reactivated by Zn [8]. In contrast 

 with this work with bacteria, it is now clear that Neurospora 

 possesses two deaminases — one specific for the L isomers of 

 threonine and serine [71], the other for the D isomers [70] 

 — and that both of these enzymes are activated by pyridoxal 

 phosphate. Biotin, AMP and GSH, either separately or 

 together, did not affect the activity of cell-free prepara- 

 tions. Though the D-serine deaminase of Esch. coli is like- 

 wise activated by pyridoxal phosphate, attempts to show 

 that the corresponding L-serine deaminase is activated by 

 this substance have been unsuccessful [43^]. Pyridoxal 

 phosphate is also reported to be the activator of the cysteine 

 desulphurase of Proteus vulgaris [48^]. In view of these 

 diverse observations, it is not yet possible to define the co- 

 factors naturally associated with the anaerobic deaminases. 

 The confusion in this field has recently been increased since 

 a substance produced by heating glucose with acid under 

 pressure was found to be as active as yeast extract in the 

 activation of the resolved aspartase system of Bact. cadaveris 

 and yet did not contain biotin [146]. Winzler, Burk and du 

 Vigneaud [61] have observed that unless biotin was added to 

 the system, washed cells of biotin-deficient Sac. cerevisiae 

 were incapable of assimilating exogenous NH|. Their ob- 

 servation can be readily explained, if, as Lichstein's work 

 indicates, this growth factor is an essential component of 

 aspartase, one of the systems by which inorganic nitrogen is 

 incorporated into organic molecules (p. 60). 



In general, the anaerobic deaminases are most active in 

 cells harvested from cultures at the cessation of active 

 cell-division. Moreover, the presence of Og favours the 

 development of the aerobic amino-acid oxidases whilst 

 anaerobic conditions favour the anaerobic deaminases. The 

 metabolic quotients of the former (QnHs about 30) are very 

 much lower than those of the latter (Qnh3=2oo-i,ooo). 

 After growth in the presence of glucose, organisms usually 

 possess poor deaminase activity, and although in general the 

 optimum pH for deaminase activity is in the range 8-10, 

 this effect cannot be explained in terms of growth in an 



