TRANSAMINATION OF 2-OXO-4-[METHYLTHIO]BUTANOIC ACID IN CHICKEN TISSUES

The keto acid 2-oxo-4[methylthio]-butanoic acid (OMTB) is an intermedi ate in the conversion of synthetic feed grade methionine sources to L- methionine in vivo in poultry and other animals. Because methionine so urces are utilized by the chick with considerably less than 100% effic iency as sources of L-methionine, it is important tb determine what me tabolic process may limit the utilization of these sources. Because OM TB is converted to L-methionine by transamination, a study was conduct ed to determine which amino acids might serve as nitrogen donors in th e conversion of OMTB to L-methionine in the chicken. Dialyzed tissue h omogenates, mitochondria, and cytosol from liver, kidney, intestine, a nd skeletal muscle were incubated with OMTB and individual L-amino aci ds (isoleucine, leucine, valine, glutamic acid, aspartic acid, alanine , glutamine, asparagine, and phenylalanine) and the methionine that ac cumulated was determined by ion exchange chromatography. Tissues diffe red in the conversion of OMTB to methionine: kidney was most active, l iver and intestinal mucosa were intermediate, and skeletal muscle had lowest activity. All amino acids supported methionine Synthesis. Branc hed-chain amino acids and glutamic acid were the most effective substr ates in tissue cytosols except in intestinal mucosa, in which asparagi ne was also effective. The preferred substrates in mitochondria were g lutamate in liver mitochondria, isoleucine and alanine in kidney mitoc hondria, and branched-chain amino acids and glutamic acid in skeletal muscle mitochondria. All amino acids except alanine supported methioni ne synthesis from OMTB in mitochondria of intestinal mucosa. We conclu de that a wide variety of amino acids can serve as substrates for tran samination of OMTB in the chicken, and that the availability of nitrog en donors is unlikely to be a limiting factor in the conversion of OMT B to methionine.