ISSN:
0091-7419
Keywords:
Life Sciences
;
Molecular Cell Biology
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
,
Chemistry and Pharmacology
,
Medicine
Notes:
1In the stimulation of rat hepatic adenylyl cyclase by glucagon or epinephrine we observe an abrupt change in the energy of activation at 32°C (seen as an increase in the slope of the Arrhenius plot). The energy of activation for the cyclase reaction above 32°C is about 1.7 times that found below this temperature. Cyclase activity stimulated by fluoride, prostaglandin E1, or 1-propanol, or activity in the absence of added stimulators does not show this change. The structural differences between the hormones suggest that they interact with the cyclase system at different loci. But the mechanism by which they stimulate cyclase activity appears to involve a common, temperature-dependent step.2In the presence of 1-propanol the change at 32°C in the energy of activation of the hormone-stimulated activity is not observed.3In view of the relatively large mole fraction of cholesterol present in the rat liver plasma membrane (which appears to inhibit phase transitions in bulk membrane lipids), it is suggested that this thermal sensitivity resides in protein rather than lipid components or that the cyclase is restricted to cholesterol-poor membrane regions.4The occurrence of anomalous Arrhenius plots of enzyme activities (with abrupt changes of slope) for both membrane-bound and soluble enzymes is reviewed.
Additional Material:
5 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jss.400010415
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