Abstract
Bradykinin-inactivating activity of mononuclear leukocytes was examined using guinea-pig macrophages and lymphocytes. Intact macrophages rapidly inactivated bradykinin. Bradykinin-inactivating activity of macrophages was present in the membrane and cytosol fractions but not in the nuclear and granular fractions. The bradykinin-inactivating activity of the membrane fraction was inhibited by captopril, whereas that of the cytosol fraction was inhibited by N-ethylmaleimide. Bradykinin-inactivating activity of intact macrophages was inhibited by captopril but not by N-ethylmaleimide, suggesting that the membranebound bradykinin-inactivating enzyme rather than the cytosol bradykinin-inactivating enzyme is responsible for the inactivation of bradykinin by intact macrophages. Although intact lymphocytes hardly inactivated bradykinin, lymphocytes contained a bradykinin-inactivating activity in the cytosol fraction but not in the nuclear and particulate fractions. The bradykinin-inactivating enzyme of the lymphocyte cytosol fraction was inhibited by N-ethylmaleimide, and this enzyme was hardly released extracellularly from intact cells during incubation of lymphocytes with bradykinin.
