Quantitative determination of protein of bacterial origin

Several methods have been developed for the determination of the proportion of nitrogen-containing substances of microbial origin in the digestive tra cts of cattle. These include assays that use nucleic acids and adenosine tr iphosphate as indicators, radioisotopes S-35, N-15, P-32 and P-33 incorpora ted into bacterial protein and phospholipids, duodenal amino acid compositi on with amino-ethylphosphonic acid, diaminopimelic acid and D-alanine(D-Ala ) contents as indicators. On the basis of the data in the literature on D-a mino acid content of milk and milk products the authors came to the conclus ion that D-glutamic acid (D-Glu) and D-aspartic acid (D-Asp) can be conside red as markers for proteins of bacterial origin. To demonstrate this, exper iments have been carried out and some of the results are reported here. (C) 2001 Elsevier Science B.V, All rights reserved.