Stimulation by thyrotropin of horse thyroid plasma membranes adenylate cyclase: evidence of cooperativity

Horse thyroid plasma membranes were prepared by partition in an aqueous two phases system. The membrane fraction was enriched in adenylate cyclase and only slightly contaminated with mitochondria and lysosomes. Adenylate cyclase activity was stimulated by TSH and PGE₁. The TSH stimulatory effect was nearly immediate and occured in the same range of concentrations that activates intact cell metabolism. It was potentiated by GTP and ITP. A quantitative analysis of the data suggests that activation of thyroid adenylate cyclase by TSH is a cooperative process.