430 2. ANALOGS OF ENZYME REACTION COMPONENTS 



some of the disturbances by interfering with pyruvate metabolism, but no 

 work has been done on the metabolic changes in tissues resulting from 

 such levels of the analog. Hydroxyphenylpyruvate is similarly formed from 

 tyrosine. 



(. ))— CH2— CH- COO" 

 Phenylalanine 



The formation of acetoin from pyruvate in Streptococcus fecalis is inhibited 

 13% by 1 mM and 75% by 10 mM phenylpyruvate, whereas the formation 

 of acetoin from acetoacetate is unaffected by 10 mM (Dolin and Gunsalus, 

 1951). Pyruvate oxidase is inhibited to about the same degree. Several 

 anaerobic pyruvate pathways are inhibited by phenylpyruvate in several 

 bacteria and yeast, including the formation of acetoin, the phosphoroclastic 

 reaction, and decarboxylation, whereas the oxidative metabolism of pyru- 

 vate is not so readily affected (Watt and Werkman, 1954). The concentra- 

 tions of pyruvate and phenylpyruvate used (120 mM) are unfortunately 

 too high to be physiologically significant, but further study on extracts 

 of Aerobacter aerogenes showed competitive inhibition of acetoin formation 

 with K,„ = 123-197 mM, and K^ = 0.59-1.1 mM, so that in this case phen- 

 ylpyruvate is bound to the enzyme much more tightly than pyruvate. 

 The reduction of hydroxypyruvate to glycerate by glycerate dehydrogenase 

 from spinach is inhibited by phenylpyruvate (5%), pyruvate (34%), and 

 bromopyruvate (52%) at 10 mM (Holzer and Holldorf, 1957). These inhi- 

 bitions are competitive but rather weak. 



The most pertinent study with respect to blocking an important pyruvate 

 pathway is that of Gale (1961) on yeast pyruvate decarboxylase, which 

 reports the inhibitions given in Table 2-24. The following compounds are 

 inactive: pyruvic ethyl ester, oxalacetate, propionate, phenyllactate, phen- 

 ylalanine, acetamide, oxamate, and oxalate. One might infer that (1) the 

 C=0 group is necessary for inhibition (reduction or substitution abolishes 

 activity), and (2) the COO" group is necessary for strong inhibition (amides 

 and esters inactive). The nature of the R group in R — CO — COO" can vary 

 quite widely and it is difficult to correlate structure with activity; for 

 example, it is surprising that ketomalonate is bound so well and chloro- 

 pyruvate relatively poorly, and that oxanilate is bound so very weakly. 



