Aug 12, 1976

Human fat cell adenylate cyclase. Enzyme characterization and guanine nucleotide effects on epinephrine responsiveness in cell membranes

Biochimica Et Biophysica Acta
B CooperR I Gregerman

Abstract

Human adenylate cyclase (ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1) has been studied in preparations of fat cell membranes ("ghosts"). As reported earlier, under ordinary assay conditions (1.0 mM ATP, 5 mM Mg2+, 30 degrees C, 10 min incubation) the enzyme was activated 6-fold by epinephrine in the presence of the GTP analog, 5'-guanylyl-imidodiphosphate [GMP-P(NH)P] (Cooper, B. et al. (1975) J. Clin. Invest. 56, 1350-1353). Basal activity was highest during the first 2 min of incubation then slowed and was linear for at least the next 18 min. Epinephrine, added alone, was often without effect. but sometimes maintained the initial high rate of basal activity. GMP-P(NH)P alone produced inhibition ("lag") of basal enzyme early in the incubation periods. Augmentation of epinephrine effect by GMP-P(NH)P, which also proceeded after a brief (2 min) lag period, was noted over a wide range of substrate (ATP) concentrations. GTP inhibited basal levels of the enzyme by about 50%. GTP also allowed expression of an epinephrine effect, but only in the sense that the hormone abolished the inhibition by GTP. Occasionally a slight stimulatory effect on epinephrine action was seen with GTP. At high Mg2+ concentration (greater than 10 mM) o...Continue Reading

  • References17
  • Citations6

Citations

Mentioned in this Paper

Glucagon (rDNA)
Fat Pad
POMC wt Allele
Guanylyl Imidodiphosphate
Glucagon
Fluorides
Epinephrine Acetate
Epinephrine Measurement
Glucagon Measurement
Adenylyl Cyclase 9

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