Characteristics of the rumen proteolysis of fraction I (18S) leaf protein from lucerne (Medicago sativa L)

Abstract

1. The rate of proteolysis of fraction I (18s) leaf protein in the rumen of sheep and cattle was affected by diet and the rate on fresh lucerne ( Medicago sativa L) was three to nine times the rate on a hay + concentrate diet.2. Simultaneous rumen fermentations in vivo and in an artificial rumen showed that the rates of proteolysis of fraction I in vitro was approximately 80% of the rates in sheep.3. Using I4C uniformly-label ed fraction I protein at low concentrations, proteolysis exhibited 1st-order kinetics.Over a wide range of protein concentrations the velocity v. substrate concentration curve showed Michaelis-Menten characteristics typical of an enzyme-catalysed reaction. With rumen fluid from a hay + concentrate-fed sheep the maximum velocity was 2.6 mg protein nitrogen/l per min and the Michaelis constant was 75 mg nitrogen/]. 4. Rapid adsorption of 14CC-labelled fraction I protein onto bacterial cells preceded proteolysis. 5. Sucrose-density-gradient .malysis showed initial incorporation of "C from protein into rumen bacteria followed by partial transfer to rumen protozoa.6. No peptides were detectec during proteolysis showing that the rate-limiting step occurred during the initial stages of proteolysis. Only small amounts of free amino acids were released except for leucine, isoleucine, valine and ornithine, which showed significantly increased levels.7. Volatile fatty acids were the main 14C-labelled end products and were rapidly produced in descendingThe In the present work fraction 1 leaf protein was chosen as a suitable substrate for detailed studies on the mechanism of proteolysis. It is the major soluble protein of green leaves and functions as the ribulose-l,5-diphosphate carboxylase (EC 4 . 1 . 1 .39) of chloroplasts. Its composition varies little between plant species, its properties have been studied extensively (for review, see Kawashima & Wildman, 1970) and it is readily prepared uniformly labelled with I4C by growing plarts in an atmosphere containing 14C0,. It is probably the most abundant protein of the natural world and comprises 3 0 4 0 % of the leaf protein of lucerne

Correlation between microbial enzyme activities in the rumen fluid of sheep under different treatments

“…Bacteria have been reported to be primarily responsible for the degradation of plant protein, and protozoa were thought to only have a minor role in this metabolic activity [48]. In this regard, Wallace and Cotta [66] reported that the role of protozoa in ruminal protein degradation is mostly related to the degradation of feed particles and bacterial proteins, but their overall effect on protein degradation is still controversial.…”

“…In this regard, Wallace and Cotta [66] reported that the role of protozoa in ruminal protein degradation is mostly related to the degradation of feed particles and bacterial proteins, but their overall effect on protein degradation is still controversial. Most of the protease is cell bound [48,52]; only a small portion is extracellular [1]. In this regard, protease activities in SRFWP and EABC are higher than in CFRF.…”

Effect of protozoa on rumen protein degradation in sheep

“…(1985). The (Nugeant and Mangan, 1981 Therefore, the degradation of soluble proteins may be more intense in the defaunated than in the faunated rumen. This hypothesis is supported by the fact that proteolytic activity was higher in defaunated animals when measured using azocasein which is totally soluble.…”

Proteinase Activity in Rumen Ciliate Protozoa

“…The proteolytic bacteria are mainly involved in the degradation of plant protein (Nugent & Mangan, 1981), whereas the rumen ciliate protozoa are thought to degrade bacterial and insoluble particulate proteins (Hino & Russell, 1987;. The predation of the bacteria by ciliates increases the rate of bacterial protein turnover (Wallace & McPherson, 1987) and decreases the efficiency of bacterial growth in the rumen (Veira, 1986), and defaunation (i.e.…”