Limit-peptide pigments of approximately 7800 and 1500 molecular weight were isolated from a humidified insulin-glucose-U-14C reaction system. Gel chromatographic analysis of the intact model system and analyses of the amino acid and carbohydrate compositions of the limit-peptide pigments indicated cross-linking between peptide chains. This cross-linking was associated with extensive condensation of sugar residues, some of which have already reacted with amine groups on the protein, into aggregates of up to 31 residues. These results give credence to the hypothesis that extensive carbohydrate condensation is required for the formation of brown chromophores [Hurd, C.

A method is described for the isolation and purification of protein-bound, brown pigments formed in protein-carbonyl browning reactions. The procedures include isoelectric washing of the protein, hydrolysis with proteolytic enzymes, and chromatographic purification by gel filtration and ion exchange chromatography. Some characteristics of the purified pigments are presented. Rahway, N.J.Preparation of Reaction System. The milk powder was

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