title: Regulation of cAMP-dissociation kinetics in lactating rat mammary gland.
abstract: The cAMP-dissociation kinetics of rat mammary gland cytosols are dependent upon the temperature of cAMP association. Dissociation rates (measured at pH 6.5, 24 degrees C) were biphasic (k = 0.08-0.23 min-1 and k = 0.02 min-1) and monophasic (k-1 = 0.02 min-1) after 0 degrees C and 24 degrees C association, respectively. The temperature-dependent change from an initial fast rate to an initial slow rate was observed at all concentrations of cAMP tested from 1 to 1000 nM. When the slow-dissociating site was associated with non-radioactive 8-bromo-cAMP, the dissociation rates of [3H]-cAMP from the remaining dissociating site was slow (k = 0.02 min-1) and fast (k = 0.05 min-1) at 24 degrees C and 0 degrees C associating rate can be converted to the slow-dissociating rate by warming. When 0.2 M sodium thiocyanate was added to the association mixture at 24 degrees C, biphasic dissociation rates of k = 0.23 min-1 and k = 0.02 min-1 were observed, suggesting that the chaotropic salt blocks the interconversion of rates. The data are consistent with the model for cAMP-dependent protein kinase which exhibits two binding sites with different affinities. The type II enzyme from mammary gland cytosol exhibits in addition the phenomenon of temperature-dependent interconversion of the two binding affinities.
mesh_terms: D015124:8-Bromo Cyclic Adenosine Monophosphate; D000818:Animals; D001665:Binding Sites; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D005260:Female; D007700:Kinetics; D007774:Lactation; D008321:Mammary Glands, Animal / Q000187:drug effects / Q000378:metabolism*; D011247:Pregnancy; D051381:Rats; D013696:Temperature; D013861:Thiocyanates / Q000494:pharmacology
chemical_list: D013861:Thiocyanates; D015124:8-Bromo Cyclic Adenosine Monophosphate; C024553:sodium thiocyanate; D000242:Cyclic AMP