Adenyl cyclase and "ATPase" in rat corpus luteum. I. Some properties of the enzymes

Interations of gonadotropins with corpus luteum membranes. VII. Association of hCG-binding and adenylate cyclase activities with rabbit corpus luteum plasma-membranes

Previous studies with rat luteal cell plasma membranes indicated a dissociation of hCG binding sites and adenylate cyclase activity. The hormone binding sites were associated with a light membrane (d 1.13) fraction derived from the microvillous surface while the cyclase enzyme was associated with a heavy membrane (d 1.17) fraction derived from the basolateral surface of the cell. In this study of plasma membranes from 8-day pseudopregnant rabbit corpora lutea both hCG binding and adenylate cyclase activity were associated with a light membrane (d 1.13) fraction. No heavy membrane material was detected.

Stabilization and solubilization of bovine corpus-luteum adenylate cyclase. The effects of guanosine triphosphate, guanosine 5'-[beta,gamma-imido]triphosphate, sodium fluoride and Tris/hydrochloric acid concentration on enzyme activity

1. Adenylate cyclase of the washed 600g sediment of bovine corpus-luteum homogenate is stimulated by p[NH]ppG (guanosine 5'-[beta,gamma-imido]triphosphate), the imido analogue of GTP, and to a lesser extent by GTP itself. Activation by p[NH]ppG is not reversed by extensive washing before assay, but can, however, be reversed by NaF. 2. Both p[NH]ppG and NaF stabilize the enzyme during incubation at 37 degrees C. NaF also causes an irreversible activation, but only of part of the potentially NaF-activatable adenylate cyclase; there are possibly two components of the adenylate cyclase system, which can be distinguished by their response to NaF. 3. Solubilization of the adenylate cyclase activity in the 600g sediment, by using the non-ionic detergent Lubrol-PX, gave variable yields. A relationship between the magnitude of NaF stimulation of the 600g-sediment enzyme and the yield of soluble activity derived from the sediment was recognized. The results suggest that the pre-existing state of the enzyme complex in vivo is reflected by the response in vitro to NaF and may determine the success with which activity can be solubilized. 4. The absolute yields of soluble activity could be increased by p[NH]ppG preactivation of the 600g sediment. During the development of the maximally active state by preincubation with p[NH]ppG the enzyme passes through a stage in which Lubrol solubilization is increased, but the maximally active state is itself less amenable to solubilization. p[NH]ppG activation causes the appearance of NaF-inhibited states, which appear to be preferentially solubilized by Lubrol-PX.

Properties of detergent-solubilized adenylate cyclase and gonadotropin receptors of testis and ovary

The relationship between solubilized hormone-binding sites and adenylate cyclase was examined in detergent extracts of particulate testis and ovarian fractions. Both basal and fluoride-stimulated activities of the particulate enzyme were markedly increased in the presence of detergents, and about 60% of the enzyme activity was recovered as the soluble form in the 300,000 g supernatant. Enhancement of adenylate cyclase activity was more marked with Lubrol PX and WX than with Triton X-100, and the highest recovery and activation of adenylate cyclase were obtained with 0.5% Lubrol PX. The particulate and solubilized testicular enzymes were more active in the presence of Mn2+, and the detergent-extracted soluble ovarian cyclase showed a small and inconstant response to gonadotropin. Fractionation of Lubrol-solubilized testis and ovarian preparations on Sepharose 6B showed two peaks of free gonadotropin receptors. The binding activity eluted with Kav of 0.32 corresponded to the receptor sites previously characterized in detergent-solubilized gonadal particles, and was coincident with the elution profile of adenylate cyclase activity. An additional peak of binding activity with Kav of 0.56 was not accompanied by detectable adenylate cyclase activity. These observations suggest that the peak of larger molecular size could represent dissociated receptors or binding sites which were not coupled to adenylate cyclase.