THE INTERFERENCE OF CYSTEINE THIOLS IN THE DETECTION OF GLYCATED AND NON-GLYCATED PROTEINS BY MODIFIED SILVER STAINING AFTER SODIUM DODECYLSULFATE-POLYACRYLAMIDE GEL-ELECTROPHORESIS

In the previous study a staining intensification of in vitro glycated collagen type I versus a non-glycated one after sodium dodecyl sulfate -polyacrylamide gel electrophoresis (SDS-PAGE) under a modified silver staining procedure was observed (Hodny, Z., Struzinsky, R. and Deyl, Z. (1992) J. Chromatogr. 578, 53-62). While investigating the specifit y of this stain to glycation product(s) on protein we have observed th at a great number of proteins (e.g. bovine serum albumin) was sensitiv e to this stain even in a non-glycated state. It is proposed from resu lts of the analysis of amino acid composition of these proteins that t heir better stainability correlates with the amount of cysteine presen t in the protein. Modification of SH groups by iodoacetamide (or N-eth ylmaleimide) had an inhibitory effect on the staining of bovine serum albumin (and some other proteins) in its 'native' state but had no vis ible inhibitory effect on their staining in the glycated state. Howeve r, the positive staining response of a great number of components from cellular lysates even after iodoacetamide treatment indicates the exi stence of further chemical groups (either of protein or nucleic acid o rigin) participating in this silver staining method.