Differences in the apparent molecular weight of soluble and mitochondrial hexokinases of rat brain

I n B rain tissue only 10–20 percent of the total hexokinase activity (EC 2.7.1.1) is present in the cytoplasm whereas the particulate activity is associated with mitochondria (B achelard , 1967; T eich-graber , B iesold and P igarewa , in press). Either small (W ilson , 1968) or insignificant kinetic differences (T hompson and B achelard , 1970; B igl , M üller and B iesold , 1971) between soluble and particulate enzyme activity have recently been reported. Though the DEAE cellulose column chromatography patterns of both hexokinases were reported to be similar (T hompson and B achelard , 1970; B igl , M üller and B iesold , 1971), differences were found between soluble and mitochondrial hexokinase after gel electrophoresis separation (B achelard , 1967; B igl , M uller and B iesold , 1971). Recently it has been shown in this laboratory that Triton X-100 also enhances the hexokinase activity of the cytoplasm as has already been demonstrated for the mitochondrial form (in preparation).
The purpose of the experiments described here was to elucidate whether the soluble cytoplasmic hexokinase differs from the mitochondrial-bound hexokinase in respect to its apparent molecular weight. To diminish the occurrence of experimental artefacts, different extraction procedures were employed. Furthermore, the effect of Triton X-100 on the molecular weight was investigated in an attempt to reveal an explanation for the increase in enzymic activity after incubation of hexokinase with this detergent.