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Degradation of Soluble and Insoluble Proteins by Bacteroides Amylophilus Protease and by Rumen Microorganisms^{1 ,2,}

Animal Research Institute, Agriculture Canada, Ottawa, Ontario, Canada K1A 0C6

Abstract

Various soluble and insoluble proteins (6.25 mg) were incubated at 37 C with partially purified protease from Bacteroides amylopbilus (156 µg) in 2.0 ml of .1 M potassium phosphate buffer, pH 7.6, for 2, 4, 6 and 18 hr, and the liberated amino acids were determined by the ninhydrin method. Results showed that (1) although soluble, serum albumin and ribonuclease A were resistant to hydrolysis; (2) soluble and insoluble proteins of soybean meal were hydrolyzed at almost identical rates; (3) soluble proteins from soybean meal, rapeseed meal and casein were hydrolyzed at different rates, and (4) treatment of resistant proteins (serum albumin, ribonuclease A and insoluble fish meal and rapeseed meal proteins) with mercaptoethanol in 8 M urea or oxidation with performic acid rendered these proteins susceptible to hydrolysis. It is concluded that (1) solubility or insolubility of a protein is not by itself an indication of the protein's resistance or susceptibility to hydrolysis by rumen bacterial protease; (2) structural characteristics of the proteins may be important, and (3) one of the properties which renders feed protein resistant to degradation is the presence of crosslinking disulfide bonds.

¹ Contribution No. 878 from the Anim. Res. Inst.

² The authors acknowledge the help of Dr. R. M. Teather in identifying and growing cultures of Bacteroides amylopbilus and Mr. L. R. Beaton for technical assistance.

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