Influence of the concentration of the protease from Streptomyces griseus relative to ruminal protein degradability

The effects of enzyme concentration and time of incubation upon protein deg radation were examined using protease from Streptomyces griseus. In the fir st experiment six samples of feeds were used to determine saturation kineti cs and extent of protein degradation, Saturation occurred only at very high and impractical concentrations (>33 U/ml) that caused excessive degradatio n. The concentration that came closest to expected in vivo degradation base d on (literature values) was about 3.3 U/ml. In the second experiment 14 fe eds with known in situ degradation values obtained from other laboratories were degraded using enzyme concentrations of 0.33, 1.0, 2.4, 3.3 and 6.6 U/ ml and for 0, 4, 8, 12, 18, 24, 36 and 48 h. Most of the enzyme-time combin ations gave high correlations with the in situ values. However, high concen trations and longer times tended to overdigest and low concentrations and s horter times to underdigest. Deviations from unity provided a measure of th e over- or underdigestion, Enzyme concentrations were estimated for zero de viation at the respected times of incubation. These values are inversely pr oportional to the time of incubation and provide a continuous function betw een time and concentrations. Any time-concentration combination can be chos en for valid laboratory measurement using a batch incubation. Analysis of t he regression of enzyme concentration upon the reciprocal of time indicated a lag time for the in vitro relative to the in situ, which was about 1.9 h . The in vitro extents of digestion were calculated using a rate of digesti on derived from the time sequence digestion data, and this value integrated with a 6% rate of passage (same as that used in the calculation of the in situ data). When deviations from unity were regressed upon logarithm of enz yme concentration, a single value for optimal enzyme concentration of 1.5 U /ml was obtained, which is less than the 3.3 value observed with thr litera ture values. A procedure is offered by which in vivo and in situ values cou ld be calibrated for enzymatic activity. (C) 1999 Elsevier Science B.V.