Decay of hexokinase during reticulocyte maturation: is oxidative damage a signal for destruction?

Proteolysis of hexokinase in cell-free systems prepared from rabbit reticulocytes has been shown previously to be ATP-dependent and apparently mediated by the ubiquitin system (Magnani et al. J. Biol.Chem.261, 8327-8333). We have investigated this phenomenon, but found no substantial loss of hexokinase in cell-free systems prepared from fresh lysates. Storage of lysates at -20 degrees C or addition of a free radical generating system was required to demonstrate rapid ATP-dependent decay. It appears that initial oxidative damage to hexokinase does not abolish its activity but allows it to be recognized by an ATP-dependent proteolytic system. The relevance of this mechanism to in vivo degradation of hexokinase is discussed.