Plasma Amino Acid Patterns in Sheep Receiving Abomasal Infusions of Methionine and Cystine

Abstract

Plasma amino acid patterns were studied in sheep receiving varying amounts of DL-or L-methionine (0'6-10·0 g/day) or L-cystine (2·0 and 8·0 g/day) as abomasal supplements or DL-methionine (10 g/day) as a dietary supplement.Total amino acids in plasma decreased when small amounts (0'6-2'5 g/day) of methionine were infused, but increased substantially with the larger amounts of methionine (4'9-10·0 g/day). However, when methionine and taurine were excluded, the remaining amino acids decreased with all amounts of methionine. Cystine supplementation caused smaller changes in total amino acids.Methionine infusions significantly increased the concentration of methionine, cystine, taurine, and cystathionine in plasma. Cystine infusions increased the concention of the latter three compounds, but not that of methionine. Infusion of small amounts of methionine (0· 6-2 . 5 g/ day) produced only small increases in plasma methionine; with the infusion of larger amounts plasma methionine increased rapidly. The relationship between plasma methionine and amount of methionine infused was described by two straight lines which intersected at about 3 . 3 g/ day of methionine. With an infusion of 10 g/day the mean plasma methionine concentration was 235 ",moles/ 100 ml, which represented 64% of the total plasma amino acids. In contrast, an equimolar amount of cystine (8 g/day) produced only a small increase in plasma cystine, and had no effect on plasma methionine.Infusions of both methionine and cystine caused considerable reductions in the plasma concentrations of the branched-chain amino acids (valine, leucine, and isoleucine), and of serine and glycine.Dietary supplements of methionine (10 g/day) caused no change in the total concentration of amino acids in plasma nor in the concentration of any individual amino acid.

A Survey of Methionine Adenosyltransferase and Cystathionine "g-Lyase Activities in Ruminant Tissues

“…Although the transsulphuration pathway permits the conversion of methionine to cyst(e)ine, the evidence suggests a rate-limiting step in that pathway. Reis et al (1973b) observed that when sheep were given abomasal infusions oflarge amounts of methionine, free methionine in plasma was elevated nearly IOO-fold, but only relatively low concentrations of free taurine and cystine were to be found. They speculated that this apparent bottleneck in the metabolism of methionine may be due to a reduced availability of serine, since plasma serine concentration is reduced, or to a decrease in cystathionine p-synthase activity, or both.…”

Evaluation of feather meal as a source of sulfur amino acids for growing steers.

“…A dietary requirement, however, exists only for Met (Reis et al, 1973), because Cys can be synthesized from Met. The reverse reaction does not occur.…”

Silage and dairy cow production

“…The effect of methionine supplementation on the increased plasma methionine levels has also been observed by Reis & Tunks (1971) and by Reis et al (1973). Cysteine and a-amino-nbutyric acid also increased presumably because they are products of methionine metabolism (Finkelstein 1974).…”