Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.1.1 (hexokinase)
 5,274 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In rabbit reticulocytes, the hexokinase (EC 2.7.1.1)-specific activity is 4-5 times that of corresponding mature red cells. Immunoprecipitation of hexokinase by a polyclonal antibody made in vitro shows that this maturation-dependent hexokinase decay is not due to accumulation of inactive enzyme molecules but to degradation of hexokinase. A cell-free system derived from rabbit reticulocytes, but not mature erythrocytes, was found to catalyze the decay of hexokinae activity and the degradation of 125I-labeled enzyme. This degradation is ATP-dependent and requires both ubiquitin and a proteolytic fraction retained by DEAE-cellulose. Maximum ATP-dependent degradation was obtained at pH 7.5 in the presence of MgATP. MgGTP could replace MgATP with a relative stimulation of 0.90. 125I-Hexokinase incubated with reticulocyte extract in the presence of ATP forms high molecular weight aggregates that reach a steady-state concentration in 1 h, whereas the degradation of the enzyme is linear up to 8 h, suggesting that the formation of protein aggregates precedes enzyme catabolism. These aggregates are stable upon boiling in 2% sodium dodecyl sulfate, 3% mercaptoethanol and probably represent an intermediate step in the enzyme degradation with hexokinase and other proteins covalently conjugate to ubiquitin. That hexokinase could be conjugated to ubiquitin was shown by the formation of 125I-ubiquitin-hexokinase complexes in the presence of ATP and the enzymes of the ubiquitin-protein ligase system. Thus, the decay of hexokinase during reticulocyte maturation is ATP- and ubiquitin-dependent and suggests a new physiological role for the energy-dependent degradation system of reticulocytes.
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PMID:Rabbit red blood cell hexokinase. Decay mechanism during reticulocyte maturation. 301 48

In rabbit erythrocytes hexokinase (EC 2.7.1.1) specific activity is 4-5 times that of corresponding mature red cells. Immunoprecipitation of hexokinase by an in vitro made policlonal antibody shows that this maturation dependent hexokinase decay is not due to the accumulation of inactive enzyme molecules but to degradation of hexokinase. A cell-free system made from rabbit reticulocytes, but not mature erythrocytes, was found to catalyze the decay of hexokinase activity and the degradation of 125I-labeled enzyme. This degradation is ATP-dependent and requires both ubiquitin and a proteolytic fraction retained by DEAE-cellulose. 125I-hexokinase incubated with reticulocyte extract in the presence of ATP forms high molecular weight aggregates. These aggregates are stable upon boiling in 2% sodium dodecyl sulfate, 3% mecaptoethanol and probably represent an intermediate step in the enzyme degradation with hexokinase and other proteins covalently conjugate to ubiquitin. That hexokinase could be conjugate to ubiquitin was shown by the formation of 125I-ubiquitin-hexokinase complexes in the presence of ATP and the enzymes of the ubiquitin-protein ligase system. Thus, the decay of hexokinase during reticulocyte maturation is ATP and ubiquitin dependent and involves both the hexokinase molecular forms (hexokinase Ia and Ib) present in reticulocytes. "In vivo", hexokinase Ia is mitochondrial bound while hexokinase Ib is soluble. The energy dependent degradation system of reticulocytes is active only on the soluble enzyme, namely hexokinase Ib. As the cell mature mitochondria are degradated, hexokinase Ia becomes soluble but there is a concomitant decay also of the proteolytic system resulting in a mature erythrocyte that contains only hexokinase Ia in a soluble form.
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PMID:Decay mechanisms of rabbit hexokinase during reticulocyte maturation. 359 95