Studies on hexokinase: 1. The hexokinase activity of rat-brain extracts

This and the two following papers are part of an investigation which was originally undertaken to study the possibility ofusing the hexokinase reaction for the assay of hormonal changes in human blood. For this purpose it seemed inadvisable to use purified hexokinase preparations, since the inter- action with hormones might conceivably depend on the association of the enzyme with other tissue constituents. Preliminary experiments had shown that aqueous extracts of rat brain possessed a hexokinase activity which was higher, more stable and more reproducible than similar extracts of rat muscle. Moreover, these extracts were practically free of carbohydrate and of codehydrogenases and their apyrase activity was low. Undesirable side reactions were therefore less likely to occur. For these reasons most experiments were performed with an aqueous extract ofrat brain as a source of hexokinase. In this paper the properties of the enzyme system used, together with some new observations on brain hexokinase, will be described.