Unexpected collagen crosslinking observed during in vitro radiolabeling of the galactosyl moiety.

Aldehyde groups, generated by oxidation of free primary alcohol groups of galactosyl residues of glycoproteins by galactose oxidase, can react with free amino groups on the polypeptide chain through Schiff base formation. Subsequent reduction with tritiated borohydride results in the formation of stable crosslinks instead of the expected generation of radiolabeled alcohol groups. Attempts to perform in vitro radiolabeling of collagen type I by this procedure resulted in undesirable crosslinking with profound alteration of the physical properties that rendered the resulting radiolabeled preparation unsuitable for biochemical studies.