Abstract
Hexokinase activity was found in both soluble (cytosolic) and particulate subcellular fractions prepared from rat pancreatic islet homogenates. The bound enzyme was associated with mitochondria rather than secretory granules. Relative to the total hexokinase activity, the amount of bound enzyme was higher in islet homogenates prepared at pH 6.0 (72 ± 7%) than in islets homogenized at pH 7.4 (38 ±1%). The affinity of hexokinase for equilibrated d-glucose was not different in the cytosolic and mitochondrial fractions. In both fractions, hexokinase displayed a greater affinity for α- than β- d-glucose, but a higher maximal velocity with the β- than α-anomer. Glucose 6-phosphate inhibited to a greater extent cytosolic than mitochondrial hexokinase. A high K m glucokinase-like enzymic activity was also present in both subcellular fractions. It is proposed that the ambiguity of hexokinase plays a propitious role in the glucose-sensing function of pancreatic islet cells.
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