The interference of cysteine thiols in the detection of glycated and non-glycated proteins by modified silver staining after sodium dodecyl sulfate-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 specificity of this stain to glycation product(s) on protein we have observed that a great number of proteins (e.g. bovine serum albumin) was sensitive to this stain even in a non-glycated state. It is proposed from results of the analysis of amino acid composition of these proteins that their better stainability correlates with the amount of cysteine present in the protein. Modification of SH groups by iodoacetamide (or N-ethylmaleimide) had an inhibitory effect on the staining of bovine serum albumin (and some other proteins) in its 'native' state but had no visible inhibitory effect on their staining in the glycated state. However, the positive staining response of a great number of components from cellular lysates even after iodoacetamide treatment indicates the existence of further chemical groups (either of protein or nucleic acid origin) participating in this silver staining method.