Evidence of existence of two isozymes of carbonic anhydrase in the anterior pituitary gland of female rats.

Two molecular forms of carbonic anhydrase were identified in the rat anterior pituitary gland. Electrophoretic and immunological studies disclosed that the low activity carbonic anhydrase (type B) was associated with the particulate fraction of the pituitary gland and the high activity carbonic anhydrase (type C) was localized in the soluble fraction. The 800 times g pellet contained 50% of the total activity of a pituitary homogenate prepared in 0.25 M sucrose, while the 105,000 times g supernatant accounted for an additional 30% of the total. The particulate enzyme was rendered soluble by treatment with Trition X-100. The activity of pituitary gland carbonic anhydrase was about 6 times greater in preparations from female rats as compared with males. The activity of carbonic anhydrase in the particulate fraction decreased, and the activity in the soluble fraction increased without a change in total activity following incubation in vitro of pituitary glands. The intracellular adjustment in enzyme activity was accompanied by the secretion of prolactin into the incubation medium by the pituitary gland. The secretion of prolactin and the solubilization of the particulate carbonic anhydrase was inhibited when the pituitary gland was incubated in the presence of 10-5 M dopamine.