Blood clearance and organ distribution and tissue concentration of native, homopolymerized and IgG-conjugated ribosome-inactivating proteins.

1. The blood clearance, organ distribution and tissue concentration of several native, homopolymerized, and IgG-conjugated 125I-labelled ribosome-inactivating proteins (RIPs) were determined in mice. 2. Native RIPs were cleared rapidly from blood, with half-lives of 4-8 min, and were concentrated mainly in the kidneys. 3. After conjugation to IgG the three RIPs studied showed increased blood half-lives and decreased concentrations in the kidneys. 4. The two homopolymers studied had blood half-lives and kidney concentrations intermediate to those of free and conjugated RIPs. 5. These results indicate that after IgG-conjugation the increased half-lives of the RIPs studied were at least in part due to the larger molecular size of the conjugates and to their lower renal excretion.