Abstract
Abstract 1. The reversible dissociation of lactic and malic dehydrogenases has been studied in detail and compared with the dissociation properties of triosephosphate dehydrogenase, α-glycerophosphate dehydrogenase, and liver alcohol dehydrogenase. 2. Evidence is presented for the existence of an intermediate form of lactic dehydrogenase with catalytic properties altered during reactivation. 3. The technique of reversible dissociation has been used to prepare interspecies hybrids of lactic, malic, and triosephosphate dehydrogenases. 4. Some of the catalytic and immunological properties of hybrid malic dehydrogenases have been examined. 5. The effects of salts on the reactivation of malic dehydrogenases have been investigated and related to previous results on lactic dehydrogenases. It is proposed that the observed salt effects may result from changes in the activity coefficients of the exposed peptide and amide groups.
Highlights
We have extended our studies of reversible inactivation of dehydrogenases to include a comparison of lactic dehydrogenase and malic dehydrogenase with triosephosphate dehydrogenase, a-glycerophosphate dehydrogenase, and liver alcohol dehydrogenase
Enzyme activity of cr-glycerophosphate dehydrogenase was determined by measuring the initial rate of oxidation of DPNH
We have previously shown that the degree of substrate inhibition by pyruvate increases as enzyme activity reappears and eventually approaches a level comparable to untreated enzyme; this change in catalytic property was accompanied by a change in the degree of hybridization of beef Hq and chicken Hq [1]
Summary
2. Evidence is presented for the existence of an intermediate form of lactic dehydrogenase with catalytic properties altered during reactivation. Preliminary evidence for the existence of at least two catalytically active forms of lactic dehydrogenase during reactivation from guanidine hydrochloride was presented. Various aspects of these studies have been examined in further detail and reversible inactivation by lithium chloride, as well as guanidine, acid, and urea, has been demonstrated. A previous report from this laboratory described the effects of various factors which modify the rates and extents of reactivation of lactic and malic dehydrogenases after these enzymes had been inactivated by guanidine hydrochloride, urea, or low pH [1].
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