Effect of Borate on the Catalytic Activities of Muscle Glyceraldehyde‐3‐Phosphate Dehydrogenase

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Abstract
The effect of borate on glyceraldehyde-3-phosphate dehydrogenase from human, pig and rabbit muscle was studied. A lower concentration of borate only the dehydrogenase activity is inhibited, reversibly and competitively against NAD. At concentration of borate above 6 mM the plots of 1/v vs. borate concentration become nonlinear, and the inhibition is extended to the esterase and acetylphosphatase activities. In certain conditions a time-dependent inactivation and reactivation was observed. The direct interaction between borate (if present at concentration of at least 6 mM) and glyceraldehyde-3-phosphate dehydrogenase is postulated, the possible site of the reaction being the histidine residue(s). The esterase activity of the human muscle enzyme and the effect of borate on it are different from the other mammalian enzymes.