SOME ASPECTS OF PYRIDOXAL PHOSPHOKINASE IN CHICK BRAIN1

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Abstract
Abstract— The activity of pyridoxal phosphokinase (EC 2.7.1.35) has been studied in two brain areas of the White Leghorn chick during post‐hatch development. Activities of this enzyme were approximately the same in both forebrain and cerebellum at 2 days of age but when maximum activity was reached, at 20‐25 days, the enzyme activity in forebrain was considerably higher than in the cerebellum. In homogenates, the activity of pyridoxal phosphokinase (as measured by pyridoxal phosphate formation) was inhibited by a particulate‐bound inhibitor. In the forebrain of the 15‐day‐old chick, this inhibitor was detected in concentrations 3‐ to 5‐fold greater than in the cerebellum. The inhibitor appeared to be an atypical ATPase which approached adult levels in the chick forebrain by two days after hatching. The possible physiological significance as well as the possible artifactual nature of this pyridoxal phosphokinase inhibitor in the in vitro assay system has been considered.