BIOSYNTHESIS OF THE TWO CHAINS OF INSULIN

* Supported in part by the U.S. Public Health Service, grant AI 03962, from the National Institute of Allergy and Infectious Diseases. t A unit of the New York State Department of Health. 1 Simpson, R. T., J. F. Riordan, and B. L. Vallee, Biochemistry, 2, 616 (1963). 2 Vallee, B. L., J. F. Riordan, and J. E. Coleman, these PROCEEDINGS, 49, 109 (1963). 3 Pressman, D., and 0. Roholt, these PROCEEDINGS, 47, 1606 (1960). 4Roholt, O., G. Radzimski, and D. Pressman, Science, 141, 726 (1963). 5 In the case of the I"25 label it is important to use some 1131 along with the Ili2 as a composite label rather than pure I'2 as the label. In subsequent steps of this procedure, the iodinated peptides derived from a mixture of the iodinated proteins are separated on paper chromatograms and their positions located by radioautography. Peptides containing IJ25 alone may be lost since the radioactivity of I"25 exposes film relatively poorly. The I131 is added to the I"25 so that the positions of the I125-labeled peptides are well marked. The amount of iodinated peptide from the Ii3"labeled enzyme present in any spot is calculated from the total I131 in the spot less the I131 on the Il25-labeled peptides in the spot. The I125/I131 ratio is based on this corrected I131 value. 6The following abbreviations are used: Cpase, carboxypeptidase; H.V.P.E., high-voltage paper electrophoresis; MIT, monoiodotyrosine; DIT, diiodotyrosine; MIH, monoiodohistidine; DIH, diiodohistidine. 7Roholt, O., A. Shaw, and D. Pressman, Nature, 196, 773 (1962). 8 Bird, R., and H. E. A. Farran, J. Clin. Endocrinol. Metab., 20, 81 (1960). 9 Dube, S. K., 0. A. Roholt, and D. Pressman, J. Biol. Chem., 239, 1809 (1964).