A MODIFIED YEMM AND COCKING NINHYDRIN REAGENT FOR PEPTIDASE ASSAY

A modified Yemm and Cocking ninhydrin–cyanide reagent has been developed which gives quantitative color yields with free amino acids, but much lower yields with most peptides tested. Using this reagent, a more sensitive assay for peptidase activity has been developed, and its use in column fractionation of peptidase activity is described.The ϵ values for peptides, obtained with the modified reagent, are compared to those obtained with the conventional ninhydrin–hydrindantin reagent. The formation of Ruhmann's Purple by the modified reagent is inhibited by Tris buffer. No inhibition occurs with the ninhydrin–hydrandantin reagent. The absorption spectra of the two reaction mixtures indicate that Tris reacts in a different manner with the two reagents.