CHARACTERIZATION OF THE PROTEOLYTIC ACTIVITY OF COMMERCIAL PROTEASES AND STRAINED RUMINAL FLUID

The objective of this research was to formulate a mixture of commercia l proteases that would mimic the rate and extent of protein degradatio n obtained using strained ruminal fluid. The proteolytic activity of s trained ruminal fluid and several commercial proteases was characteriz ed using 13 L-amino acid p-nitroanilides as artificial substrates. A m ixture of Streptomyces griseus protease, chymotrypsin, and proteinase K at .042, 2.5, and .5 enzyme units/mL, respectively, was similar to t he activity of strained ruminal fluid against the same artificial subs trates. However, degradative activities were different in incubations with feed proteins as substrates. The rates of degradation of expeller soybean meal, solvent soybean meal, and casein were .08, .05, and .08 /h, respectively, using the enzyme mixture and .03, .15, and .24/h usi ng strained ruminal fluid. A second experiment compared degradative ac tivity of S. griseus protease at .066 enzyme units/ mt, ficin at .5 en zyme units/mL, and a mixture of trypsin, carboxypeptidase B, chymotryp sin, and carboxypeptidase A at 116.6,.5, 2.5, and .5 enzyme units/ mi, respectively. Protein degradation rates obtained with strained rumina l fluid were two to six times faster than those obtained with the enzy me mixtures. A third experiment compared the degradability of 15 feed proteins with the mixture of trypsin, carboxypeptidase B, chymotrypsin and carboxypeptidase A to that with strained ruminal fluid. Degradati on rates obtained using strained ruminal. fluid ranged from .007 to .2 17/h; degradation rates using the enzyme mixture ranged from .010 to . 079/h and were lower (P =.004) than with strained ruminal fluid. Overa ll, the experiments indicated that the commercial enzymes tested did n ot mimic the protein degradative activity of strained ruminal fluid.