Archive image from page 251 of Currents in biochemical research, 1956;. Currents in biochemical research, 1956; twenty-seven essays charting the present course of biochemical research and considering the intimate relationship of biochemistry to medicine, physiology, and biology currentsinbioche1956gree Year: 1956 ( EFRAIM RACKER these specific interactions in intact cells (5). This investigation represents a new and important approach to the steady-state kinetics of intracellular metabolism. THE MICROCYCLES OF ENZYME-SUBSTRATE INTERACTIONS Catalysis may be looked upon, in many instances, as a
Archive image from page 251 of Currents in biochemical research, 1956;. Currents in biochemical research, 1956; twenty-seven essays charting the present course of biochemical research and considering the intimate relationship of biochemistry to medicine, physiology, and biology currentsinbioche1956gree Year: 1956 ( EFRAIM RACKER these specific interactions in intact cells (5). This investigation represents a new and important approach to the steady-state kinetics of intracellular metabolism. THE MICROCYCLES OF ENZYME-SUBSTRATE INTERACTIONS Catalysis may be looked upon, in many instances, as a cyclic process in which the catalyst undergoes reversible changes. Evidence for this thesis has been obtained in the case of the few enzymes which have been closely examined from this point of view. The enzymologist, hardened by his experiences with com- plex metabolic cycles, now begins to turn to the exploration of enzymes as 'microcycles.' 6-l-P E-P E G-l,6-P G-6-R Figure 2. Phosphoglucomutase catalyzes the reversible transformation of glucose-1-phosphate (G-l-p) to glucose-6-phosphate (G-6-p). The reaction was first written as G-l-p<=G-6-p. When the func- tion of glucose-l,6-diphosphate (G-l,6-p) as a coenzyme was discovered (28), the reaction was written as: G-l-p + G-l,6-p«= G-1,6-p + G-6-p. With the elucidation of the role of the enzyme protein as phosphate acceptor (32), the reaction sequence can be represented by a cyclic process which includes all reactants, as shown in Figure 2. The enzyme occurs in muscle extracts as phosphoenzyme (E-p). In the presence of the substrate (either G-l-p or G-6-p), the phosphate group is transferred and glu- cose-1,6-diphosphate is formed. The latter then returns the phosphate to the enzyme and forms the product (G-6-p or G-l-p). 230
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