Reticulocyte lipoxygenase, ingensin, and ATP‐dependent proteolysis

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Abstract
Lipoxygenase purified from rabbit reticulocyte lysate has a molecular mass of 68 kDa on SDS gel and a pI of 5.97. Lipoxygenase is inhibited by nordihydroguaiaretic acid (NDGA), 3‐amino‐1‐(m‐(trifluoromethyl)phenyl)‐2‐pyrazoline (BW755C), 5,8,11,14‐eicosatetraynoic acid (ETYA), salicylhydroxamate (SHAM) or hemin. Metal ions or nucleotides do not affect its activity. The addition of certain of these inhibitors to the reticulocyte extract also inhibited the ATP‐dependent proteolysis of casein, one of the distinct characteristics of reticulocytes. No clear correlation between lipoxygenase activity and ATP‐dependent proteolysis could be detected. Hemin and NDGA inhibited both processes, but the concentrations necessary for inhibition were quite different. SHAM completely inhibited lipoxygenase, but not proteolysis. o‐Phenanthroline inhibited ATP‐dependent proteolysis, but had no effect on lipoxygenase activity. We have also purified a high‐molecular‐mass protease, ingensin, from reticulocyte extract. This protease accounted for more than 90% of the casein‐degrading activity in reticulocyte extract. NDGA inhibited ingensin at the same concentrations required for inhibition of ATP‐dependent proteolysis. These results suggest that lipoxygenase is not indispensable for the ATP‐dependent proteolysis and the novel high‐molecular‐mass protease, ingensin, may be involved in the process.