Comparative Characterization of Glutamate Decarboxylase in Crude Homogenates of Oviduct, Ovary, and Hypothalamus

Abstract

Some biochemical characteristics of L-glutamate decarboxylase (GAD) were compared using crude homogenates of the rat oviduct, ovary, and hypothalamus. As estimated by the measurement of CO2 production, the specific activities of oviductal and ovarian GAD were about 10 and 3% of the hypothalamic value, respectively. Stoichiometric formation of GABA and CO2 from L-glutamate could be observed in oviduct and hypothalamus, while in ovarian homogenates the production of CO2 was > 9 times that of GABA. Hypothalamic and tubal GAD showed similar time course, temperature dependence, and pH dependence. The dependence on protein concentration and on exogenous cofactor supply was also similar in these 2 tissues. The kinetic constant for L-glutamate as a substrate was nearly the same in oviduct (1.30 mM) and hypothalamus (1.64 mM). The responsiveness of tubal and hypothalamic GAD to various inhibitors was also similar. The oviductal and the hypothalamic GAD may be identical, and they suggest a possible GABAergic innervation of the Fallopian tube.