Pulmonary angiotensin-converting enzyme antienzyme antibody

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Abstract
A method was developed for quantitating anticatalytic activity in antibody preparations made in goats against pure solubilized angiotensin-converting enzyme (EC 3.4.15.1) from rabbit pulmonary membranes. Anticatalytic activity was purified about 90-fold from a single batch of serum by a precedure including DEAE-cellulose chromatography and elution from Sepharose columns containing covalently bound pure enzyme. Antiholoenzyme antibody was fractionated with respect to charge and binding affinity; these different populations each inhibited enzymatic hydrolysis of hippurylhistidylleucine, angiotensin I and bradykinin. The inhibition dose-respose curves were similar for hydrolysis of hippurylhistidylleucine and angiotensin I despite the difference in molecular weight of these substrates. Evidence is presented suggesting that a single molecule of antibody can bind 2 molecules of enzyme and that at least 18% of the total antiholoenzyme antibody population is directed against determinants which influence catalytic activity. A competititive immunoassay was developed with radioiodinated pulmonary enzyme as displaceable antigen. The anticatalytic and radioimmune assays were used to examine immunological properties of converting enzymes in various rabbit organs and fluids. Kidney, brain and serum contained converting enzymes which were immunologically identical with that in rabbit lung. Converting enzyme in seminal plasma was similar to the lung enzyme in the anticatalytic assay, but showed lower immunoreactivity in the radioimmune assay.