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Enhancement of parathyroid hormone‐responsive renal cortical adenylate cyclase activity by a cytosol protein activator from rat reticulocytes
Author(s) -
Shane Elizabeth,
Avioli Richard C.,
Greene Virginia S.,
Yeh Mary,
Owens John M.,
Bell Norman H.,
Bilezikian John P.
Publication year - 1986
Publication title -
journal of bone and mineral research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.882
H-Index - 241
eISSN - 1523-4681
pISSN - 0884-0431
DOI - 10.1002/jbmr.5650010108
Subject(s) - cyclase , adenylate kinase , adenylate cyclase toxin , endocrinology , biology , medicine , biochemistry , pertussis toxin , receptor , g protein
Abstract The effects of the cytosol activator protein obtained from rat reticulocytes (RCAP) were investigated in a heterologous membrane system — partially purified cell membranes from dog renal cortex. RCAP enhanced the response of dog renal cortical adenylate cyclase to bovine parathyroid hormone (1–34) [bPTH (1–34)] from two‐ to three‐fold. RCAP also enhanced the response to 5 μ M arginine vasopressin, 10 μ M glucagon, and 10 μ M isoproterenol. Analysis of double‐reciprocal plots of substrate concentration and enzyme activity indicated that bPTH (1–34) alone and together with RCAP increased the V max of the adenylate cyclase enzyme and did not alter the apparent K m of the enzyme for MgATP. Membranes from dog renal cortex contain 42K and 39K proteins that are ADP‐ribosylated by cholera toxin and pertussis toxin, respectively, and appear to be the stimulatory (N s ) and inhibitory (N i ) guanine nucleotide binding proteins described in many other hormone‐responsive membrane preparations. Similar to its effects in rat reticulocytes, RCAP inhibited ADP‐ribosylation of N s and enhanced ADP‐ribosylation of N i . The muscarinic agonist, carbachol, inhibited PTH‐responsive adenylate cyclase activity in dog renal cortical membranes and this inhibition was reversed by RCAP. These results indicate that RCAP enhances stimulation of adenylate cyclase by a variety of hormones in a heterologous membrane preparation and supports the hypothesis that RCAP's site of action is common to all adenylate cyclase systems. RCAP may facilitate coupling between N s and the catalytic unit of adenylate cyclase by a pertussis toxin‐like effect to inactivate N i . The dual effects of RCAP upon ADP‐ribosylation of N i and N s α subunits suggest that a binding site for RCAP may exist at a site of homology between N Sα and N iα .