Aug 1, 1976

A kinetic analysis of a catechol-specific binding site in the microsomal fraction from the rabbit aorta

European Journal of Pharmacology
R R RuffoloP N Patil

Abstract

(-)-3/-Norepinephrine (3H-NE) binding to the microsomal fraction of the rabbit aorta has been studied. Binding appears to increase linearly with time up to at least 30 min, shows no evidence of stereoselectivity and may be inhibited only by compounds possessing the catechol or 3-methoxy-4hydroxyphenyl moieties, with the latter being 100-fold less effective. 3H-NE binding is saturable with a Km of 8.5 X 10(-8) M and V max of 28 pmoles/mg protein. A Hill plot indicates that binding is noncooperative whereas a Scatchard plot suggests that two sites may be present. Binding does not appear to require physiological concentrations of Ca2+ or Mg2+ and is inhibited significantly by EDTA and sodium metabisulfite. In addition, binding is markedly enhanced by low and high pH values. This binding is also inhibited by sodium metabisulfite which suggests that an oxidized form of the catecholamine is the active binding species. Experiments with several group specific reagents indicate that binding may require a free sulfhydryl group but not a carboxyl function. The binding process requires an energy of activation of 14.8 kcal/mole whose magnitude may be partly explained, with the aid of optical rotatory dispersion spectra, by a non-stereoslect...Continue Reading

Mentioned in this Paper

Calcium
Microsomes
Norepinephrine, (+, -)-Isomer
Chinchilla Rabbits
Edetic Acid, Sodium Salt
Catechols
Descending Aorta
Hydrogen-Ion Concentration
Edetic Acid, Calcium, Sodium Salt
In Vitro [Publication Type]

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