Tricyclohexyltin hydroxide effects on cationic and substrate activation kinetics of beta-adrenergic–stimulated cardiac Ca2+-ATPase
✍ Scribed by Sahib, Kabeer I. Ahammad ;Desaiah, Durisala
- Publisher
- John Wiley and Sons
- Year
- 1986
- Tongue
- English
- Weight
- 633 KB
- Volume
- 1
- Category
- Article
- ISSN
- 0887-2082
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✦ Synopsis
Previous studies from this laboratory have indicated that tricyclohexyltin hydroxide (Plictran) is a potent inhibitor of both basal-and isoproterenol-stimulated cardiac sarcoplasmic reticulum (SR) Ca2+-ATPase, with an estimated IC-50 of 2.5 x 1W8M. The present studies were initiated to evaluate the mechanism of inhibition of CaZ+-ATPase by Plictran. Data on substrate and cationic activation kinetics of CaZ+-ATPase indicated alteration of V , , , and K, by Plictran (1 and 5x104M), suggesting a mixed type of inhibition. The betaadrenergic agonist isoproterenol increased V , , , of both ATP-and Ca2+-dependent enzyme activities. However, the K, of enzyme was decreased only for Ca2+.
Plictran inhibited isoproterenol-stimulated Ca2+-ATPase activity by altering both V , , and K,,, of ATP as well as Ca2+-dependent enzyme activities, suggesting that after binding to a single independent site, Plictran inhibits enzyme catalysis by decreasing the affinity of enzyme for ATP as well as for CaZ+. Preincubation of enzyme with 15 pM CAMP or the addition of 2mM ATP to the reaction mixture resulted in slight activation of Plictran-inhibited enzyme. Pretreatment of SR with 5 x lW'M propranolol and 5 x lo-8M Plictran resulted in inhibition of basal activity in addition to the loss of stimulated activity. Preincubation of heart SR preparation with 5 x lW5M coenzyme A in combination with 5 x l P M Plictran partly restored the beta-adrenergic stimulation. These results suggest that some critical sites common to both basal-and beta-adrenergic-stimulated CaZ+-ATPase are sensitive to binding by Plictran, and the resultant conformational change may lead to inhibition of beta-adrenergic stimulation.