Synthesis of bovine lutropin in cell-free lysates containing pituitary microsomes.

Bovine pituitary rough microsomes were used to determine the ratio of newly synthesized lutropin (LH) alpha and beta subunits in different physiological states of animals. Proteins synthesized by microsomal runoff are derived from preinitiated mRNAs and thus, in the present case, should reflect the initial intracellular steady state levels of the subunits. The products were identified by immunoprecipitation using bovine LH subunit specific antisera and analyzed by electrophoresis on sodium dodecyl sulfate-polyacrylamide gels. Microsomes isolated from castrated animals (steers) synthesized comparable amounts of LH alpha- and LH beta-subunits as determined by quantitation of the immunoprecipitated products. However, microsomes from intact animals (bulls) directed the synthesis of 3-5 times more alpha than LH beta. A comparison of the levels of alpha- and LH beta-subunits synthesized by an equivalent concentration of bull and steer pituitary microsomes indicates that the increased ratio of alpha to LH beta in bull pituitary microsomes is the result of a preferential decrease in the synthesis of the LH beta subunit. The results suggest that the rate of beta subunit synthesis determines the level of intact LH produced.