PHOSPHOINOSITIDE KINASES IN CHICK BRAIN AND SCIATIC NERVE, A DEVELOPMENTAL STUDY

Abstract

Abstract—Phosphatidylinositol kinase and diphosphoinositide kinase activities were measured in homogenates of brain and sciatic nerve of developing chick embryos and chicks. Characteristics of the chick nervous system enzymes were similar to those reported for rat brain. Diphosphoinositide kinase was inhibited by high concentrations of ATP and by low concentrations of triphosphoinositide. Both activities were greatly enhanced by the non‐ionic detergent, Cutscum, and the ratio of detergent to protein in the reaction mixture was important. Optimum phosphatidylinositol kinase activity required a ratio of 7 : 1 for both tissues. The optimum ratio for diphosphoinositide kinase was 3:1 for nerve homogenates and 0.6:1 for brain. Cutscum increased the concentration of diphosphoinositide that is required for maximum diphosphoinositide kinase activity.Developmental changes were the same for both kinase activities, which were low in unmyelinated brain and sciatic nerve. The activities correlated with the concentration of polyphosphoinositides in chick brain where they increased 4‐5 fold during the period of active myelination and remained high in the mature brain. The kinase activities correlated with the rate of triphosphoinositide deposition in sciatic nerve. Following a 2‐3 fold increase during the initial phase of myelination the activities declined to values as low as those of embryonic nerve.