GLUTAMINE TRANSAMINASE-K AND OMEGA-AMIDASE ACTIVITIES IN PRIMARY CULTURES OF ASTROCYTES AND NEURONS AND IN EMBRYONIC CHICK FOREBRAIN - MARKED INDUCTION OF BRAIN GLUTAMINE TRANSAMINASE-K AT TIME OF HATCHING

Glutamine transaminase K and omega-amidase activities are present in t he chick brain and in the brains of adult mice, rats, and humans. Howe ver, the activity of glutamine transaminase K in adult mouse brain is relatively low. In the chick embryo, cerebral glutamine transaminase K activity is low between embryonic days 5 and 17, but by day 23 (day o f hatching) activity rises dramatically (> 15-fold). Cerebral omega-am idase activity is relatively high at embryonic day 5 but lower between days 5 and 17; at embryonic day 23 the activity rises to a maximum. B oth glutamine transaminase K and omega-amidase are present in cultured chick, rat, and mouse astrocytes and neurons. For each species, the a ctivity of glutamine transaminase K is higher in the astrocytes than i n the neurons. The activity of omega-amidase is about the same in the cultured chick astrocytes and neurons but significantly higher in rat astrocytes than in rat neurons. The data suggest that the rise in brai n glutamine transaminase K activity in the chick embryo at hatching co rrelates with maturation of astrocytes. Glutamine transaminase K may b e involved in glutamine cycling in astrocytes. Glutamine transaminase K appears to be a major cysteine S-conjugate beta-lyase of the brain a nd may play a role in the neurotoxicity associated with exposure to di chloroacetylene and perhaps to other toxins.