Adenylate cyclase activity in Y1 mouse adrenocortical tumor cells: some properties of the enzyme associated with purified plasma membrane fractions

Abstract

Fractions enriched in plasma membranes were prepared from the Y1 mouse adrenocortical tumor cell line and were characterized with respect to adenylate cyclase activity. Optimal requirements of the adenylate cyclase system for guanyl nucleotides. Mg2+, ATP, and corticotropin (ACTH) were determined. The sensitivity of the adenylate cyclase system to ACTH in plasma membrane fractions was comparable with that observed in isolated intact cells. Polycations such as poly-L-arginine and histone competitively inhibited the action of ACTH, supporting the view that the affinity of ACTH for the adenylate cyclase system is determined by the basic core of amino acids at residues 15-18. ACTH was at least one order of magnitude more potent than ACTH in stimulating adenylate cyclase activity in plasma membrane fractions.

Defective guanyl nucleotide-binding protein beta gamma subunits in a forskolin-resistant mutant of the Y1 adrenocortical cell line.

“…Plasma membrane-enriched fractions were prepared by differential centrifugation over discontinuous sucrose gradients (15) until use. Detergent extracts were prepared by suspending membranes, at a protein concentration of 4 mg/ml, in buffer A (20 mM Tris HCl, pH 8.0/1 mM EDTA/1 mM dithiothreitol/100 mM NaCi) containing 1% cholate for 1 hr at 40C, followed by centrifugation at 100,000 x g for 1 hr to remove insoluble material.…”