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Regulation of Adenosine‐Sensitive Adenylate Cyclase from Rat Brain Striatum
Author(s) -
AnandSrivastava Madhu B.,
Johnson Roger A.
Publication year - 1980
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1980.tb07089.x
Subject(s) - adenosine , cyclase , medicine , adenylate kinase , endocrinology , stimulation , gtp' , chemistry , dopamine , biology , biochemistry , enzyme
An adenosine‐sensitive adenylate cyclase has been characterized from rat brain striatum. In whole homogenates as well as in particulate fractions, N 6 ‐phenylisopropyl adenosine (PIA), 2‐chloroadenosine, and adenosine N ′‐oxide were equipotent in stimulating adenylate cyclase. Although GTP inhibited basal as well as PIA‐stimulated activity of whole homogenates, the enzyme showed an absolute dependency on GTP for stimulation by PIA, dopamine, epinephrine, and norepinephrine in a particulate fraction derived from discontinuous sucrose gradient centrifugation. Adenosine exerts two effects on this adenylate cyclase, stimulation at low concentrations and inhibition at high concentrations, suggesting the presence of two adenosine binding sites. The stimulation of adenylate cyclase by PIA was dependent on the concentration of Mg 2‐ . The degree of stimulation by PIA was greater at a low concentration of Mg 2+ , which suggests that stimulation by PIA was accompanied by increasing the apparent affinity for Mg 2+ . Activation of adenylate cyclase by PIA was blocked by theophylline or 3‐isobutyl‐ 1‐methylxanthine (IBMX). The pH optimum for basal or (PIA + GTP)‐stimulated activities was broad, with a peak between 8.5 and 9.5. In the presence of GTP, stimulation by an optimal concentration of PIA was additive, with maximal stimulation by the catecholamines. Phospholipase A 2 treatment at a concentration of 1 U/ml for 5 min completely abolished the stimulatory effect of dopamine, whereas PIA‐stimulated activity remained unaltered. These data suggest that rat brain striatum either has a single adenylate cyclase, which is stimulated by catecholamines and adenosine by distinct mechanisms, or has different cyclase populations, stimulated by either adenosine or catecholamines.