Concerning the use of empirical methods for determining the molecular weight of a small glycopeptide cleaved from bovine rhodopsin

Abstract

The molecular weight of a glycopeptide cleaved enzymatically from bovine rhodopsin was investigated by a variety of techniques, such as gel filtration, sodium dodecyl sulfate-polyacrylamide gel electrophoresis in the presence and absence of urea, and gel filtration in 6 M guanidinium chloride after reduction and carboxymethylation. Great variation in the estimation of the molecular weight between the several techniques was observed. When compared to an estimate of 9000 based on amino acid analysis and considerations of its carbohydrate content, values ranging between 4500 and 18,000 were obtained by the other methods. Thus, while the molecular weight of the glycopeptide remains unresolved, the resultant ambiguity in evaluating this property may exemplify the limitations inherent in applying empirical methods to the determination of the molecular weight of small glycopeptides.