The effects of glycoprotein modification on beta-adrenoreceptors binding ability in rat cardiac membranes

The present study was designed to test the effects of neuraminidase and some proteolytic enzymes on the binding of 125I-HYP (hydroxybenzylpindolol) to beta-adrenoreceptors of rat cardiac membranes. The influence of some S-S and -SH active agents on the ligand binding used was also examined. The decrease in membrane sialic acid content did not alter the binding of ligand used. The degradation of membrane protein by proteases resulted in a time and enzyme type dependent decrease in the binding of 125I-HYP. It was found that the dithiotreitol pretreatment produced more profound decrease in ligand binding than reduced glutathione. Cysteine and mercaptoethanol were ineffective. The effect of dithiotreitol was dependent on the time of preincubation and on the agent concentration used. The decrease in ligand binding was also observed after the alkylation of -SH groups by iodoacetamide and N-ethylmaleimide.