Somatomedin A and B: demonstration of two different somatomedinlike components in human plasma.

Abstract

This chapter discusses the presence of two different somatomedinlike components in human plasma. Assay methods were developed for the estimation of sulfate uptake in monolayer cultures of human glial cells, fibroblasts, or chick chondrocytes. An enhanced uptake of 35 SO 4 , obeying a linear dose–response relationship, was demonstrated after stimulation of the cultures with appropriate amounts of human serum. The 35 S-labeled chondroitin sulfate recovered from stimulated chondrocyte cultures had the same degree of sulfation, the same ratio of chondroitin 4-sulfate to chondroitin 6-sulfate and the same macromolecular behavior on gel chromatography as that isolated from nonstimulated cultures. A preparation of somatomedin (SM) from human plasma stimulated both sulfate uptake in chick cartilage and thymidine uptake in human glial cells or fibroblasts. Gel chromatography on Sephadex G-75, high voltage paper electrophoresis at pH 2, and isoelectric focusing showed that the cartilage factor was not identical with the glial or fibroblast factor, but differed both in regard to charge properties and molecular size. The tentative designations SM-A and SM-B were suggested for the cartilage and glial-fibroblast-stimulating factors, respectively.