270 2. ANALOGS OF ENZYME REACTION COMPONENTS 



Germination of Bacillus cereus spores is induced by certain amino acids, 

 such as L-alanine, and it would appear in this case that L-alanine dehydro- 

 genase is essential for the activation process (O'Connor and Halvorson, 

 1961 b). D- Alanine and some other analogs, such as D-a-amino-w-butyrate, 

 inhibit the germination when it is induced by L-alanine, and also inhibit 

 the oxidative deamination of L-alanine and to a lesser extent other amino 

 acids, there being a good correlation between these two inhibitory actions 

 in the series of analogs used (see accompanying tabulation). The inhibition 



% Inhibition of deamination 

 Substrate ^^ D-alanine (100 mi/) 



L-Alanine 61 



L-a-Amino-?i-butyrate 59 



L-Norvaline 48 



L-Serine 28 



L-Valine 24 



L-Cysteine 15 



L-Isoleucine 12 



L-Leucine 



L-Phenylalanine 



by D-alanine is, however, by no means specific for L-alanine. It is possible 

 that several enzymes, with different susceptibilities to D-alanine, are in- 

 volved in the deamination of the various amino acids. 



An interesting illustration of optical specificity is provided by the 0- 

 phosphoserine phosphatase from chicken liver (Neuhaus and Byrne, 1960), 

 Both L-phosphoserine and D-phosphoserine are substrates and both l- 

 serine and D-serine inhibit. The L-serine is a much more potent inhibitor 

 (see accompanying tabulation), l- Alanine also inhibits, being between 



l- and D-serine in potency, but D-alanine does not inhibit. The inhibition 

 by L-serine seems to be uncompetitive from a double reciprocal plot, but 



