On the introduction of disulfide crosslinks into fibrous proteins and bovine serum albumin.

Hydroxyl groups in serine side chains of collagen, silk fibroin, and bovine serum albumin (BSA) were converted to SH by tosylation. In collagen film, 50% of the serine OH groups could be thiolated at most. In fibroin, only 13% because of its compact beta-pleated sheet structure and low susceptibility to swelling. The SH groups introduced are near enough together to form -S-S- bonds by oxidation. The residual SH content after oxidation was 0.1% in collagen and 0.03 to 0.25% in fibroin. Disulfide crosslinking increased the shrinkage temperature of collagen and fibroin and decreased the amount of shrinkage. BSA was crosslinked to dimers (MBSA) according to gel permeation chromatography and sedimentation analysis by the analytical centrifuge. Because these crosslinked proteins can be metabolized by the usual processes, in contrast to those crosslinked by artificial, nonphysiological bridges, they may be used for biological or medical purposes.