Among the major cardenolides from the milkweed Asclepias asperula, 6'-O-(E-4-hydroxycinnamoyl) desglucouzarin has not been characterized biochemically. In this study, its binding affinity for a physiological receptor, porcine kidney Na+,K+-ATPase, was found to be lower than the other cardenolides in this plant. The order of affinities from highest to lowest was: uzarigenin (K(d) = 1.05 μM) = desglucouzarin (K(d) = 0.98 μM) > uzarin (K(d) = 4.0 μM) > 6'-O-(E-4-hydroxycinnamoyl) desglucouzarin (K(d) = 16 μM). The chemical attachment of the 4-hydroxycinnamoyl group to the 6'-carbon of desglucouzarin significantly inhibits binding. This agrees with predictions that a 5'-methyl group on cardenolides fits the receptor site optimally for the porcine kidney enzyme. The 4-hydroxycinnamic ester was also found to be fluorescent.
enzyme inhibitor, cardiac glycoside, cardenolide, Asclepias, Asclepias asperula, desglucouzarin, kidney enzyme, urarin, uzarigenin
NCBI PubMed ID: 9790942Publication DOI: 10.1006/bbrc.1998.9453Journal NLM ID: 0372516Publisher: Academic Press
Institutions: Department of Chemistry and Physics, Louisiana State University at Shreveport, Shreveport, US
Methods: fluorescence spectroscopy, inhibition assay
Found