MERCAPTOETHANESULPHONIC ACID AS A PROTECTING AND HYDROLYZING AGENT FOR THE DETERMINATION OF THE AMINO-ACID-COMPOSITION OF PROTEINS USING ANELEVATED-TEMPERATURE FOR PROTEIN HYDROLYSIS

Mercaptoethanesulphonic acid (MES-OH) (3 M) was used for the hydrolysi s of different samples (pure proteins, free tryptophan and milk powder with a high sugar content). Different temperatures (160, 170 and and 180 degrees C) and time periods (15-90 min) were compared under standa rd conditions to minimize side-reactions in order to obtain the best r ecovery of the amino acids (especially tryptophan and methionine). The materials used for testing the hydrolysis methods were bovine ribonuc lease, lysozyme, cytochrome c, free tryptophan and mare's milk powder. Hydrolysis at high temperature was successfully applied for the amino acid analysis of milk powder with high contents of carbohydrate and p ure proteins. In some instances, such as in tryptophan and methionine determination at 160-170 degrees C for 15-30 min, the results were bet ter than those obtained by the original MES-OH method. A disadvantage of the MES-OH hydrolysis method is that it reduces cystine to cysteine , which co-elutes with proline from the ion-exchange column used to se parate the released amino acids and it may interfere with the determin ation of proline in high-cystine proteins.