ENZYMES 43 



riboflavin-5-phosplioric acid (or lactoflaviii-5-pliosphoric 

 acid as it was originally called because of its isolation 

 from milk) to react in neutral solution with the carrier. 

 The enzyme carboxylase, occurring in yeast, and 

 causing the breakdown of pyruvic acid in alcoholic 

 fermentation (see p. 277) appears to be a complex of 

 aneurin diphosphate, magnesium and a protein carrier. 

 Aneurin diphosphate, 



N==C.XHo CI I ' /^^ /^^ 



I I ■* I /(J = C-CH2.CPI2.O-P-O-P-OH 



CH3.0 c — CH2 — n; I ii II 



II II \CH-S 

 2^ CH 



also occurs as the prosthetic group in pyruvic oxidases 

 occurring in Lactobacillus delhrilckii. Streptococcus 

 hae7nolyticus and gonococci and possibly in the acetic 

 acid bacteria. 



So far prosthetic groups have only been detected in 

 the endo -enzymes concerned in respiration and not in 

 the hydrolytic enzymes. 



The mechanism by which these enzymes bring about 

 their specific activities will be discussed in connection 

 with bacterial respiration in Chapter XII. 



To sum up, we may say that although we loiow a 

 little about the chemical nature of a very few of the multi- 

 tudinous enz^Tues, of the vast majority we laiow nothing 

 beyond the effects they have and the conditions under 

 which those effects are brought about. 



Physical Properties of Enzymes. — Enzymes, in general, 

 are soluble in water and in dilute alcohol, but are pre- 

 cipitated from solution by ammonium sulphate or by 

 high concentrations of alcohol or of acetone. Chemically 

 and physically they are very unstable substances, one or 

 two being so sensitive that even mechanical shaking is 

 sufficient to destroy their activity. 



