Exposure of latent prostaglandin binding sites in the rat epididymal adipocyte membrane and the effects of albumin, heating and alkylating agents

Brief incubation (1 min) of the adipocyte isolated membranes at 60°C caused an increase in prostaglandin E₂ binding, similar to that obtained with albumin. The increase in the membranal binding capacity after a short heating of the membranes was concomitant with a substantial decline in the ability of albumin to induce a further increase in the binding capacity of the treated membranes. Pretreatment of the isolated adipocyte membranes with 10 mM N-ethylmaleimide inhibited the enhancement of prostaglandin E₂ binding in the presence of albumin, but did not affect the prostaglandin E₂ binding in the absence of albumin. Identical treatment of the isolated membranes with glutathione-maleimide, an impermeable SH reagent with comparable alkylation reactivity, enhanced the binding of prostaglandin E₂ in the absence of albumin and failed to inhibit the enhancement of prostaglandin E₂ binding in its presence. In contrast to the effect of albumin on prostaglandin E₂ binding to the isolated membranes, albumin failed to alter prostaglandin E₂ specific binding to intact adipocytes.