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

Abstract

The activities of two key enzymes, methionine adenosyltransferase (EC 2.5.1.6) and cystathionine y-lyase (EC 4.4.1.1), involved in the metabolism of methionine to cyst(e)ine have been studied in the liver, heart, kidney medulla, kidney cortex, pancreas, duodenal wall, spleen and skeletal muscle in the neonatallarnb, unweaned lamb, adult sheep, pre-ruminant calf, ruminant steer and adult goat, and for comparative purposes in the adult rat.Methionine adenosyltransferase was widely distributed in the tissues of the ruminant species examined, with specific activities in the order of 10 2 nmol S-adenosylmethionine formed per milligram protein per 30 min. Greatest activities were found in liver, kidney, spleen and duodenal wall in adult ruminants, and also in skeletal muscle in pre-ruminant lambs and calves. Hepatic methionine adenosyltransferase activity declined with age in both sheep and cattle.Cystathionine y-lyase activity was not demonstrable in skeletal muscle or heart in any of the species examined. Greatest activities (in the order of 10 nmol cystathionine degraded per milligram protein per 30 min) were found in liver, kidney and pancreas for all species. Neonatal lamb tissues had the highest activities. In sheep specific activities in liver, pancreas, kidney cortex and spleen declined with age.

Tissue Metabolism of Methionine in Sheep

“…4) form a pattern similar to that described in the rat (Mitchell and Benevenga 1978). This reflects poorly the distribution of methionine adenosyltransferase (EC 2.5.1.6) and cystathionine-),-lyase (EC 4.4.1.1) activities between tissues of adult sheep (Radcliffe and Egan 1974), but is similar to that reported for these two enzymes in the adult rat (Finkelstein 1967). More work is required to determine whether the tissue distribution of enzymes associated with transsulfuration and transamination pathways of methionine metabolism can be correlated with observed metabolism of specifically labelled methionine by tissue homogenates.…”

“…Similar comparisons made for cystathionine-/'-lyase in homogenates from the liver and kidney showed that the activities of tissues from young rats were half those in tissues from adults. Radcliffe and Egan (1974) reported that the specific activity of methionine adenosyltransferase in the kidney of 2-week-old lambs was twice that of the 4-year-old sheep whereas activity of the same enzyme in liver from the lamb was less than half that in the older sheep. The activity of cystathionine-/,-lyase in both the kidney and liver of adult sheep was only about one-tenth the activity in the respective tissues from neonatal lambs.…”

“…5-2· O-fold difference in the rate of conversion of the carboxyl carbon of methionine to CO2 in homogenates of liver and kidney from the 2-week-and 3-month-old lambs. These results can be compared with the general pattern of development of methionine adenosyltransferase in the liver and kidney of the rat (Finkelstein 1967) and of cystathionine-),-lyase in the liver and kidney of the rat (Finkelstein 1967) and the sheep (Radcliffe and Egan 1974). Finkelstein (1967) found no change with age in the specific activity of methionine adenosyltransferase in homogenates of kidney from the rat, whereas tbat in the liver of young rats was 40% lower than that in liver from adult rats.…”

049 Physiological and molecular mechanisms associated with performance, immunometabolic status, and liver function in transition dairy cows fed rumen-protected methionine or choline

“…However, several studies have determined the developmental activity of these enzymes in sheep (Radcliffe andEgan, 1974, Xue andSnoswell, 1986) and growing steers in response to abomasal methionine supplementation (Lambert et al, 2002). It is important to note that compared with rats, sheep have lowered activity of key enzymes in the one carbon metabolism pathway.…”

Vitamin B-6 and Sulfur Amino Acid Metabolism

“…The degradation of cysteine involves activation at the y-carbon atom, whereas all of the other reactions involve activation at the s-carbon atom, and involves a separate active site on the enzyme. y-Cystathionase activity is widespread among tissues (brain, liver, kidney, pancreas) and among species--it is present at high levels in the liver of every species examined (9,10,59). In brain, the activity of this enzyme is low, and is a contributing factor, at least, to the high concentration of cystathionine found in this organ.…”