MITOCHONDRIA-BOUND HEXOKINASE FROM RABBIT RETICULOCYTES IS RESISTANT TO THE INACTIVATION INDUCED BY FE(II) ASCORBATE/

Exposure of rabbit reticulocytes to Fe(II)/ascorbate induced a pronoun ced decay in hexokinase activity. In reticulocytes, this enzyme is pre sent in at least three different molecular forms, Ia, Ia and Ib, sub- types of hexokinase type I, which show different intracellular distrib ution. Hexokinase Ia and Ib are soluble, whereas hexokinase Ia'' is al most entirely bound to the mitochondria. Anion exchange chromatography of hexokinase from intact reticulocytes exposed to Fe(II)/ascorbate r evealed a selective inactivation of forms Ia and Ib, whereas the form Ia did not show any decay. Binding to the mitochondrial membrane seem s to be responsible for the observed resistence of the form Ia'' to th e inactivation elicited by Fe(II)/ascorbate. Indeed, by using a cell-f ree system in which hexokinase Ia was solubilized using Triton X-100, the decay in hexokinase activity induced by iron/ascorbate involved a ll three enzymatic forms.