The dimer of bovine pancreatic ribonuclease to which we have coupled lactose residues will be tested in animals carrying liver tumors. The experiment is based upon the demonstrated hepatic uptake of the derivative as a result of the affinity of the carbohydrate moiety for galactose-specific receptors of the liver parenchymal cells, considered together with the independent observations on the cytotoxicity of ribonuclease dimers to tumor cells. The inhibitor of ribonuclease isolated from the human placenta will be used to study the domains in the enzyme and in the inhibitor which are most directly concerned in the highly specific interaction between the two proteins. In order to make the inhibitor more readily available as a reagent to increase the yields of proteins synthesized in in vitro systems, the most suitable mammalian source for the preparation of the pure protein will be established. The myelin-associated enzyme, 2',3'-cyclic nucleotide 3'-phosphohydrolase, which has been prepared in pure form from bovine white matter and spinal cord, will be characterized in further detail and its properties compared with those of the other major brain proteins. A corollary project will be the development of techniques for obtaining accurate amino acid analyses on proteins present in 5 microgram amounts in bands obtained by gel electrophoresis. A new deoxyribonuclease in beef kidney is being submitted to purification and characterization.