Abstract
Adenosine 2'-monophospho-5'-diphosphoribose (P-ADP-Rib) is a structural analog of NADPH which was reported to competitively inhibit (Kiapp = 21.7 microM) solubilized rat liver 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase (Tanazawa, K., and A. Endo. 1979. Eur. J. Biochem. 98: 195-201). However, microsomal HMG-CoA reductase, which at low thiol concentrations exhibits allosteric properties, is only poorly inhibited by P-ADP-Rib (Kiapp = 550 microM at 4.5 mM GSH). Gradual shift of the microsomal reductase towards a non-allosteric form by increasing glutathione (GSH) concentrations resulted in a higher inhibition by P-ADP-Rib. Under these conditions, Ki values for P-ADP-Rib were 165 microM and 53 microM at 9 mM and 27 mM GSH, respectively. The largest change in the degree of inhibition by P-ADP-Rib was observed within the 10 mM range of GSH. By contrast, freeze-thaw solubilized HMG-CoA reductase, which does not display allosteric properties, is readily inhibited by P-ADP-Rib, even when assayed at a low concentration of GSH (Kiapp = 50 microM at 4.5 mM GSH). Assaying the solubilized reductase in the presence of increased thiol concentration results in a minor decrease in the apparent Ki for P-ADP-Rib (22 microM at 27 mM GSH). Microsomal HMG-CoA reductase is allosterically activated by various nucleotides. When activated by NADH, the enzyme is effectively inhibited by P-ADP-Rib even at a 4.5-mM GSH concentration (Kiapp = 175 microM in the presence of 300 microM NADH).(ABSTRACT TRUNCATED AT 250 WORDS)
Highlights
Adenosine 2'-monophospho-5'-diphosphoribos(ePADP-Rib) is a structural analog of NADPH which was reported to competitively inhibit (Kiapp= 21.7 p ~ so)lubilized rat liver 3-hydroxy-3-methylglutarylcoenzyme A (HMG-CoA) reductase
HMG-CoA reductase was prepared by the freeze-. Based on this kinetic behavior, we proposed that thawing procedure and was partially purified as previmicrosomal HMG-CoA reductase is an allostericenzyme, undergoing conformational changes in response to allosteric effectors (e.g., NADH) and alterations in thiol ously described [24]
We have investigated the inhibition of HMG-CoA reductase by adenosine 2'-monophospho-5'-diphosphoribose (P-ADP-Rib), a structural analog of the substrate NADPH
Summary
Adenosine 2'-monophospho-5'-diphosphoribos(ePADP-Rib) is a structural analog of NADPH which was reported to competitively inhibit (Kiapp= 21.7 p ~ so)lubilized rat liver 3-hydroxy-3-methylglutarylcoenzyme A (HMG-CoA) reductase Microsomal HMG-CoA reductase, which at low thiol concentrations exhibits allosteric properties, is only poorly inhibited by P-ADP-Rib (Kiapp= 550 p~ at 4.5 mM GSH). When activated by NADH, the enzyme is effectively inhibited by P-ADP-Rib even at a 4.5-mM GSH concentration (Kiapp = 175 pM in the presence of 300 p~ NADH). These results support a proposal that thiol-dependent reduction of enzyme disulfide(s) or binding of an allosteric activator to it cause conformational changes in the microsomal reductase protein that. There is a growing number of reports on the role of thiols and disulfides in determining the activity of HMG-
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
