title: Methionine supply to growing steers affects hepatic activities of methionine synthase and betaine-homocysteine methyltransferase, but not cystathionine synthase.
abstract: The effects of supplemental methionine (Met), supplied abomasally, on the activities of methionine synthase (MS), cystathionine synthase (CS) and betaine-homocysteine methyltransferase (BHMT) were studied in growing steers. Six Holstein steers (205 kg) were used in a replicated 3 x 3 Latin square experiment. Steers were fed 2.6 kg dry matter daily of a diet containing 83% soybean hulls and 8% wheat straw. Ruminal infusions of 180 g/d acetate, 180 g/d propionate, 45 g/d butyrate, and abomasal infusion of 300 g/d dextrose provided additional energy. An amino acid mixture (299 g/d) limiting in Met was infused into the abomasum to ensure that nonsulfur amino acids did not limit growth. Treatments were infused abomasally and included 0, 5 or 10 g/d L-Met. Retained N (20.5, 26.9 and 31.6 g/d for 0, 5 and 10 g/d L-Met, respectively) increased (P < 0.01) linearly with increased supplemental Met. Hepatic Met, vitamin B-12, S-adenosylmethionine and S-adenosylhomocysteine were not affected by Met supplementation. Hepatic folates tended (P = 0.07) to decrease linearly with Met supplementation. All three enzymes were detected in hepatic tissue of our steers. Hepatic CS activity was not affected by Met supplementation. Hepatic MS decreased (P < 0.01) linearly with increasing Met supply, and hepatic BHMT activity responded quadratically (P = 0.04), with 0 and 10 g/d Met being higher than the intermediate level. Data from this experiment indicate that sulfur amino acid metabolism may be regulated differently in cattle than in other tested species.
authors.affiliation: Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506-1600, USA.
authors.forename: Barry D
authors.initials: BD
authors.lastname: Lambert
authors.forename: Evan C
authors.initials: EC
authors.lastname: Titgemeyer
authors.forename: Gerald L
authors.initials: GL
authors.lastname: Stokka
authors.forename: Brad M
authors.initials: BM
authors.lastname: DeBey
authors.forename: Clint A
authors.initials: CA
authors.lastname: Löest
mesh_terms: D013766:5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase / Q000378:metabolism*; D000375:Aging / Q000378:metabolism*; D000596:Amino Acids / Q000097:blood; D000818:Animals; D050940:Betaine-Homocysteine S-Methyltransferase; D002417:Cattle / Q000254:growth & development / Q000378:metabolism; D003541:Cystathionine beta-Synthase / Q000378:metabolism*; D008099:Liver / Q000201:enzymology*; D008297:Male; D008715:Methionine / Q000494:pharmacology*; D008780:Methyltransferases / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism; D009994:Osmolar Concentration
chemical_list: D000596:Amino Acids; D008715:Methionine; D008780:Methyltransferases; D013766:5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase; D050940:Betaine-Homocysteine S-Methyltransferase; D003541:Cystathionine beta-Synthase; D009584:Nitrogen