title: Effect of calmodulin on aldosterone synthesis by a cytochrome P-45011 beta-reconstituted system from bovine adrenocortical mitochondria.
abstract: Bovine adrenocortical calmodulin was purified and its general properties were examined. The latter were similar to those of bovine brain calmodulin. When added to a cytochrome P-450(11)beta-reconstituted system in the presence of dilauroylphosphatidylcholine, calmodulin decreased the rate of aldosterone production from corticosterone from 0.8 to 0.1 nmol/(min X nmol P-450), while it increased the rate of 18-hydroxycorticosterone production from 1.8 to 4.6 nmol/(min X nmol P-450). This effect of calmodulin on steroid production was maximum at a concentration of 1 microM, when 1 microM cytochrome P-450(11)beta was used. The effect was dependent on the presence of Ca2+, and maximal response was observed at less than 1 microM Ca2+. There was essentially no difference in the effect when bovine brain calmodulin was used. Calmodulin induced a change in the activity of cytochrome P-450(11)beta in the presence of a wide concentration range of corticosterone as a substrate. As for 18-hydroxycorticosterone production, calmodulin increased both the maximal activity and the apparent Km for corticosterone, but it decreased the apparent Km for adrenodoxin. Adrenodoxin at a concentration of less than 20 microM did not fully abolish the effect of calmodulin. A small type I difference spectrum appeared when calmodulin was added to cytochrome P-450(11)beta. The difference spectrum increased significantly in the presence of both Ca2+ and adrenodoxin. These results suggest that calmodulin interacts with cytochrome P-450(11)beta in the presence of adrenodoxin and then modulates the activity of aldosterone synthesis catalyzed by cytochrome P-450(11) beta.
mesh_terms: D000302:Adrenal Cortex / Q000378:metabolism*; D000325:Adrenodoxin / Q000302:isolation & purification / Q000378:metabolism; D000450:Aldosterone / Q000096:biosynthesis*; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002147:Calmodulin / Q000302:isolation & purification / Q000502:physiology*; D002417:Cattle; D003577:Cytochrome P-450 Enzyme System / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D008928:Mitochondria / Q000378:metabolism*; D013252:Steroid 11-beta-Hydroxylase / Q000302:isolation & purification / Q000378:metabolism*; D013250:Steroid Hydroxylases / Q000378:metabolism*; D014268:Trifluoperazine / Q000494:pharmacology
chemical_list: D000596:Amino Acids; D002147:Calmodulin; D000325:Adrenodoxin; D014268:Trifluoperazine; D000450:Aldosterone; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D013252:Steroid 11-beta-Hydroxylase; D002118:Calcium