Enzyme Inhibition by Sericea Lespedeza Tannins and the Use of Supplements to Restore Activity
Low forage quality of sericea lespedeza [Lespedeza cuneata (Dum.- Cours.) G. Don] herbage is associated with the presence of condensed tannins in the leaves, and tannin-protein complexes that render digestive enzymes inactive. Experiments were conducted to (i) determine the type of inhibition of the cellulase complex caused by tannins, (ii) evaluate N-containing supplements that preferentially bind to tannins and restore cellulase activity, (iii) determine the effect of such supplements on the in vitro dry matter digestibility (IVDMD) of cellulose, and (iv) determine their effect on IVDMD of high- and low-tannin sericea herbage. The type of enzyme inhibition was determined by Michaelis-Menten kinetics; a double-reciprocal plot of the data revealed that tannins inhibited cellulase enzymes noncompetitively. Cellulase activity in tannin-containing solutions increased with increasing amounts of N-containing supplements, except for urea. Ovalbumin, polyvinylpyrrolidone (PVP), and gelatin resulted in greatest saccharification: hemoglobin and β-casein were less effective. Gelatin, hemoglobin, PVP, and ovalbumin partially overcame the effects of exogenous tannins on IVDMD of cellulose, but the proteins were more effective than PVP. The IVDMD of herbage from high- and low-tannin cultivars was greatest when PVP or ovalbumin were added; less supplement was needed in the low-tannin cultivar. We conclude that N-containing supplements improve digestibility and, consequently, may improve the performance of animals consuming sericea lespedeza forage.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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