N-(4-Dimethylamino)-3,5-Dinitrophenyl)maleimide: A coloured sulfhydryl reagent

The coloured sulfhydryl reagent, N-(4-dimethylamino-3,5-dinitrophenyl) maleimide (DDPM), has been synthesized and its reactions with cysteine and with the free SH groups of human and bovine serum albumin have been studied. The DDPS-serum albumins, prepared from DDPM and serum albumins, were subjected to hydrolysis with pepsin. From the digests, S-DDPS-cysteine peptides were isolated by means of their yellow colour, and purified by adsorption on talc, paper ionophoresis and chromatography. The same amino acid sequence, Leu-Glu(NH2)-Asp-Glu-Glu-(NH2)-Glu-CySH-Pro-Phe, have been found to occur in the peptides derived from bovine and from human serum albumin.