Converting enzyme activity in human plasma.

Human plasma converting enzyme activity was investigated by comparing biological with immunological activity of added or generated angiotensin after plasma incubation. Sodium citrate (2 X 10" 2 M), 2:2'-dipyridyl (1 X lO 4 and 1 X 10~M), chromotropic acid (3 X 10" and 3 X K H M ) and desferrioxamine (10 and 100 mg/100 ml) did not interfere with converting enzyme. By contrast, EDTA (3 X H H M and 3 X 1 0 " 2 M ) , EGTA (3 X H H M ) , 8quinolinol (1 X 1 0 2 M ) , and oxalic acid (3 X 10~M) were shown to interfere with plasma converting enzyme activity. The EDTA inhibition of converting enzyme activity could be partially reversed by molar excess amounts of calcium, zinc and cobalt. The ability of these ions to restore converting enzyme activity to the plasma was quantitatively variable. Inhibition of converting enzyme activity by EDTA could not be reversed by the addition of iron, copper or manganese to the samples.