ENZYMES AS REAGENTS 



first clearly formulated by Bergmann (2), the kinetic ramifica- 

 tions of the polyaffinity concept of a stepwise interaction be- 

 tween substrate and enzyme, the re-evaluation of the velocity 

 constants, and the existence of complex multiheaded enzymes 

 with multifunctional catalytic activities are among the major 

 developments in this area. They have stimulated new experi- 

 mental approaches and at the same time contributed to a more 

 timid approach regarding the interpretation of kinetic data. It 

 is self-evident from the above considerations that it is very diffi- 

 cult to interpret unambiguously kinetic data obtained with crude 

 enzyme preparations which may contain inhibitors or interfering 

 enzymes. Moreover, the meaning of painstaking studies, even 

 with highly purified enzymes, may be obscured by the presence 

 of side reactions. For example, several times recrystallized 

 pyruvic kinase contains adenylic kinase, and triose phosphate 

 isomerase may be found in several times recrystallized aldolase. 

 Even pure enzymes with multiple heads, such as glyceraldehyde- 

 3-phosphate dehydrogenase, catalyze side reactions which com- 

 plicate the life of the kineticist. 



Enzymes have become accepted as analytical tools. Some 

 enzymatic methods used for determination of metabolic inter- 

 mediates (e.g., the various hexose phosphates) have a degree of 

 specificity rarely attained by colorimetric and isolation proce- 

 dures. However, the drawbacks of these enzymatic methods are 

 by no means negligible because of the rigid criteria of purity 

 which have to be applied to the reagents used. 



In recent years a few crystalline enzymes have become avail- 

 able in large quantities and have permitted an investigation of 

 their participation as reactants in the reactions they catalyze. 

 It has been possible to show that a cyclic process takes place in 

 which enzyme, coenzyme, and substrate interact to produce a 

 sequence of new intermediates. Glyceraldehyde-3-phosphate 

 dehydrogenase can be isolated as an acyl enzyme and phospho- 

 glucomutase as a phosphorylated enzyme. 



These are some of the currents and undercurrents in present 

 enzymology. What are the perspectives? Hundreds of enzymes 



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