PYRUVATE METABOLISM 429 



glucosidase, possibly involved in the digestion of cellulose, is strongly inhi- 

 bited by glucono-l,4-lactone (^, = 0.094 mM) and glucono-l,5-lactone 

 (^. = 0.091 milf ) in a competitive manner, the affinity of the enzyme for 

 these analogs being about 10 times that for the substrate o-nitrophenyl- 

 /?-glucoside, whereas gluconate itself has no action. Ox liver /?-galactosidase 

 is inhibited much more potently by the galactono- and fucono-l,5-lactones 

 than the corresponding 1,4-lactones, and this can be readily explained on 

 the basis of the relationship to substrate configuration (Lewy et al., 1962). 

 A remarkable degree of specificity is exhibited by the a and /? glycosidases, 

 inhibition usually resulting only from the corresponding aldonolactone in 

 a number of enzymes from different sources (Conchie and Lewy, 1957). 

 For example, limpet a-mannosidase is inhibited markedly by mannono- 

 1,4-lactone but not by the glucono-, galactono-, arabono-, or xylonolactones. 

 On the other hand, galactono- 1,4-lactone is specific for /?-galactosidase 

 (Conchie and Hay, 1959). Cellulytic rumen enzymes are inhibited to vary- 

 ing degrees by glucono- 1,4-lactone, depending on the substrate chain length; 

 hydrolysis of cellobiose is inhibited 99%, of cellotriose 90%, and of cellote- 

 traose 75% by 0.5 mM (Festenstein, 1959). Glucono- 1,4-lactone also inhibits 

 a yeast debranching isoamylase (Gunja et al., 1961) and a mammalian 

 thioglycosidase (Goodman et al., 1959), so that this type of inhibition ap- 

 pears to be widespread. 



Very potent and specific inhibitions are exerted on N-acetyl-/?-glucos- 

 aminidase and N-acetyl-/?-galactosaminidase by the corresponding lactones 

 (Marsh and Lewy, 1957; Findlay et al, 1958). The former enzyme from 

 epididymis is inhibited by N-acetylglucosaminolactone competitively, with 

 K- = 0.000072 mil/, but the limpet enzyme is less sensitive, the K^ being 

 0.027 mM. The N-acetyl-a-glucosaminidase, on the other hand, is inhibited 

 much less. The acetyl group is essential for the inhibition and cannot be 

 replaced by other acyl groups. Certainly the use of the corresponding lac- 

 tones for specific and potent inhibition of the glycosidases has been one of 

 the most successful endeavors in the application of analogs. 



PYRUVATE METABOLISM 



The usefulness of a direct and specific inhibitor of pyruvate utilization 

 is obvious and the natural occurrence of certain pyruvate analogs makes 

 this field of inhibitor study an important one, but relatively little work 

 has been done. Fluoropyruvate will be taken up with other fluorinated 

 compounds, such as fluoroacetate, in a separate chapter. Phenylpyruvate 

 is the best studied of the other pyruvate analogs. It is readily formed from 

 phenylalanine and is usually decarboxylated to phenylacetate, although 

 some may be reduced to phenyllactate. In phenylketonuria (phenylpyruvic 

 oligophrenia), the accumulation of phenylpyruvate could be responsible for 



