Archive image from page 252 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 ( ENZYMES AS REAGENTS Another example of a microcyclic sequence of interactions is catalyzed by giyceraldehyde-3-phosphate dehydrogenase and its pyridine nucleotide coenzyme (Figure 3). DPN combines with the SH-enzyme to form a DPN-enzyme complex (DPN-E) which can be measured by its
Archive image from page 252 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 ( ENZYMES AS REAGENTS Another example of a microcyclic sequence of interactions is catalyzed by giyceraldehyde-3-phosphate dehydrogenase and its pyridine nucleotide coenzyme (Figure 3). DPN combines with the SH-enzyme to form a DPN-enzyme complex (DPN-E) which can be measured by its absorption band at 360 lUfx. The aldehyde interacts with the DPN-enzyme to yield acyl enzyme and reduced DPN. In the presence of phosphate, the acyl enzyme is phosphorolyzed to acyl phosphate and SH-enzyme, which combines again with DPN to regenerate the DPN-enzyme complex (38). ALDEHYDE DPN-E DP N H + H l+ACCEPTOR) + PHOSPHATE A C Y L-P Figure 3. The enzyme crystallizes from rabbit muscle in the presence of ethylenediamine tetraacetate as the DPN-enzyme complex with 3 moles of DPN per mole. After removal of DPN by treatment with charcoal, the enzyme is somewhat less stable and crystallizes only with difficulty. Exposure of the charcoal- treated enzyme to acetyl phosphate results in the formation of acyl enzyme. Crystallization of the protein from this mixture occurs again quite readily and the crystalline material contains the acetyl enzyme: It gives a positive hydroxylamine test and oxidizes DPNH, thereby forming free acetaldehyde from the acetyl group. With 1,3-diphosphoglycerate, the formation of a phosphoglyceryl enzyme has been demonstrated (26). 231
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