Induction of glutamine synthetase in chick embryo retina effects of serum and of steroid structure

Abstract

Glutamine-synthetase (EC 6.3.1.2) activity in chick embryo retina can be prematurely induced in tissue culture by a variety of steroids. A number of these, e.g. prednisolone, and triamcinolone appear to be better inducers of glutamine synthetase than hydrocortisone. One or more other serum factors appear to influence the induction. It is proposed that the steroid binding proteins known to be present in sera may be among these. The influence of steroid structure on the enzyme induction is quite apparent. The C-21 hydroxyl group of the steroid does not seem to be important for induction; a variety of C-21 esters as well as 21-deoxycortisol are active. The A-ring of the steroid appears to be of utmost importance; reduction of the α,β-unsaturated keto group renders the molecule inactive. There is some suggestion that a correlation exists between structural requirements of the steroid for induction and those for optimum binding to serum proteins. In addition to inducing glutamine synthetase, the steroids appear in some way to help preserve the integrity of the retinas in culture.