Glutamic-aspartic transaminase of Dolichos lablab: participation by iron as a cofactor.

1. The action of carboxypeptidase on insulin and acetylinsulin has been investigated. The results of previous workers that the removal of C-terminal alanine does not affect the biological activity of the insulin molecule, but that removal of C-terminal asparagine does so, have been confirmed. 2. The action of trypsin on insulin has also been investigated. The peptides resulting have been purified, characterized and tested for biological activity. The peptide DHA insulin, which is insulin without the eight amino acid residues of the carboxyl end of the phenylalanyl chain, still retains about 15 % of the biological activity of the intact insulin molecule.