A pepstatin-immunometric assay for active renin in human plasma

Abstract

Renin (EC 3.4.23) is a rate-limiting enzyme in the renin-angiotensin system that regulates the water-electrolyte balance and blood pressure. Plasma renin has been assayed by measurement of plasma renin activity (PRA), because purification of human renin is very difficult and no antibody has been available for direct radioimmunoassay of human plasma renin. Recently, some groups, including ours, purified human renin [l-3] and developed direct radioimmunoassays for human plasma renin [4-61. These assays were very sensitive but detect not only active but also inactive forms of renin. To develop a specific radioimmunoassay for active renin, a monoclonal antibody specific for active has been developed [7-lo]. Another way to develop a specific assay of active renin is to use renin inhibitor as a ligand. Pepstatin-A is a synthetic inhibitor specific to aspartyl proteases including renin [ll] and, as far as we know, renin is the only aspartyl protease in human plasma. In this preliminary study we developed a new immunometric assay that was specific for the active forms of renin in human plasma. For this purpose we used solid-phased pepstatin as a ligand to separate active renin from inactive renin.