Ribonuclease inhibitors in human blood: comparative studies on the inhibitors detected in erythrocytes, platelets, mononuclear leukocytes and granulocytes.

The erythrocyte ribonuclease inhibitor (RI) and platelet RI were separately purified to homogeneity and showed similar properties to those of human brain and placental RIs. The same type of RI seemed to be present in mononuclear leukocytes and granulocytes. The RI contents of these cells were detectable by immunoblot analysis using anti-human placental RI antibody. Neither RI activity nor the molecule cross-reactive with the anti-human placental RI antibody was detectable in any plasma sample. It is intriguing to detect active RI in mature erythrocytes, where no nucleus exists and RNA metabolism is unlikely to occur.