THE HYDROLYSIS OF CASEIN BY ENZYMES WITH ESPECIAL REFERENCE TO THE DISTRIBUTION OF AMINO ACIDS IN THE HYDROLYSATE

JOHN BECK, Purdue University

Abstract

In order to gain a greater insight into the structure of proteins as affecting the relative availability of various amino acids for animal nutrition, study was made of the hydrolysis of casein by proteolytic synes with special reference to the liberation of specific amino acids.A comparative study was made of the rates of unmasking or liberation of four amino acids-tyrosine, tryptophane, histidine and arginine- in relation to one another, and to the general hydrolysis of casein.Hydrolysis of casein by pancreatin takes place very rapidly during thefirst six hours. Although most of the hydrolysis occurs during the first twelve hours, sane hydrolysis is noticed even after twenty-two hours which continues to proceed slowly for many days. When pancreatin is used to hydrolyze casein, 34 per cent of the peptide groups rain unattacked after seventy-two hours.The linkages of won amino acids are more liable to enzymatic hydrolysts than others with pancreatin or yeast proteses.Tyrosine was found to be unmasked much faster than general hydrolysis proceeds. Thus, when 90 per cent of the tyrorine has been unnaaited, only 12 per cent of the peptide linkages have been split.Tryptophane, under the same conditions, was unsasked slightly lower, being finally liberated to the extent of 85 per cent.A new method for the determination of the rate of Liberation of the basic amino acids, arginine and histidine, has been developed. These wino acids are separated from the products of enzyme hydrolysis by means of electrodialysis and subsequently determined. By this method, it has been shown that arginine and histidine are berated are slowly than tyrosine or tryptophane. After prolonged digestion, only two-thirds of the arginine was liberated while histidine was liberated almost completely. This is the first time that the rate of liberation of histidine by enzymes has been determined.

Degree

Ph.D.

Subject Area

Biochemistry

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