ABSTRACT
In cells shifted back to aerobic conditions, the adenosine triphosphate (ATP) levels were raised, the glucocorticosteroid-binding ability was restored. In this chapter, the authors present a preliminary characterization of a protein kinase (PK) copurifying with the progesterone receptor and the receptor phosphorylation by chick oviduct cells grown in primary culture. As indicated by the in vivo studies, different degrees of phosphorylation are likely to occur and may affect diverse receptor functions steroid binding, affinity for the regulatory elements of specific genes, and also receptor/heat-shock protein interactions. If there is now good evidence to suggest that receptor phosphorylation is involved in the regulation of binding activity of glucocorticosteroid and estrogen receptors, very little has been published about the progesterone receptor. More indirect evidence is also provided by the observation that the phosphatase inhibitors, molybdate and fluoride, stabilize the steroid binding ability of steroid receptors.
