G. Licitra a,*, P.J. Van Soest b, I. Schadt c, S. Carpino c, C.J. Sniffen d
a- Istituto di Scienze e Tecnologie delle Produzioni Animali, Università di Catania.Via Val di Savoia 5, 95123 Catania, Italy
b- Cornell University, 329 Morrison Hall, Ithaca, NY 14853, USA
c- Consorzio Ricerca Filiera Lattiero ± Casearia, 97100 Ragusa, Italy
d- William H. Miner Institute, Chazy, NY 12921, USA
The effects of enzyme concentration and time of incubation upon protein degradation were examined using protease from Streptomyces griseus. In the first experiment six samples of feeds were used to determine saturation kinetics and extent of protein degradation. Saturation occurred only at very high and impractical concentrations (>33 U/ml) that caused excessive degradation. The concentration that came closest to expected in vivo degradation based on (literature values) was about 3.3 U/ml. In the second experiment 14 feeds 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 combinations gave high correlations with the in situ values. However, high concentrations and longer times tended to overdigest and low concentrations and shorter times to underdigest. Deviations from unity provided a measure of the over- or underdigestion. Enzyme concentrations were estimated for zero deviation at the respected times of incubation. These values are inversely proportional to the time of incubation and provide a continuous function between time and concentrations. Any time± concentration combination can be chosen for valid laboratory measurement using a batch incubation. Analysis of the 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 digestion 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 enzyme 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 the literature values. A procedure is offered by which in vivo and in situ values could be calibrated for enzymatic activity.
Keywords: Protein, Ruminal degradability, Protease
Giuseppe Licitra
Prof. DISPA Università di Agraria Catania
caccamo@corfilac.it
