Protein Disulphide‐Isomerase Activity in Various Cells Synthesizing Collagen

Abstract

A high correlation was found between the activities of protein disulfide isomerase and prolyl 4-hydroxylase when assayed in cells synthesizing various collagen types or the same type at markedly different rates. The highest activities of both enzymes were found in freshly isolated chick-embryo tendon and cartilage cells, intermediate activities in confluent cultures of human skin and lung fibroblasts and mouse 3T6 fibroblasts, and the lowest values in 3 human sarcoma cell lines [HT 1080, Va13/W1-38, A-204]; the difference in protein disulfide isomerase activity between the freshly isolated tendon cells and confluent SV-40-transformed human lung fibroblasts being about 25-fold. All these differences are in good agreement with differences reported between the various cells in their rates of collagen synthesis. A great similarity was also found between the changes in the 2 enzyme activities measured per cell during the growth of 3T6 fibroblast cultures from the early log phase to the stationary phase. No correlation was found between protein disulfide isomerase activity and the type of collagen synthesized. Protein disulfide isomerase may be involved in the formation of intra-chain and inter-chain disulfide bonds in procollagens, but there is no collagen type-related variation in this enzyme activity of a magnitude that would explain the marked differences in the rates of formation of inter-chain disulfide bonds between the various collagen types.