Synthesis and myocardial kinetics of N-13 and C-11 labeled branched-chain L-amino acids.
Glutamate dehydrogenase (GDH), immobilized on CNBr-activated Sepharose supports, was used with N-13 ammonia to aminate alpha-ketoisocaproic acid (KIC), and alpha-ketoisovaleric acid (KIV) to produce N-13-labeled branched-chain L-amino acids with radiochemical yields ranging from 29% to 35%. From kinetic and practical considerations, pH 7.5-8.0 was established to be optimal for the synthesis of N-13-labeled branched-chain-L-amino acids. Myocardial time-activity curves in dogs at control, during low-flow ischemia, reperfusion, and after transaminase inhibition following intracoronary bolus injection of the N-13-labeled amino acids were biexponential. Higher retention of N-13 activity was observed in ischemic segments both during low-flow ischemia (29.2%) and reperfusion (23.2%) when compared with controls (20.0%), (n = 4). On the other hand, transaminase inhibition decreased residue fractions from 21.0% at control to 13.9% (n = 4). The residual activity with L-[1-11C]leucine allows for the calculation of protein synthesis rates.
D000597:Amino Acids, Branched-Chain / Q000096:biosynthesis*; D000818:Animals; D002250:Carbon Radioisotopes / Q000378:metabolism*; D003327:Coronary Disease / Q000378:metabolism; D004285:Dogs; D004800:Enzymes, Immobilized / Q000378:metabolism; D005969:Glutamate Dehydrogenase / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007930:Leucine / Q000096:biosynthesis; D009206:Myocardium / Q000378:metabolism*; D009590:Nitrogen Radioisotopes / Q000378:metabolism*; D000637:Transaminases / Q000037:antagonists & inhibitors; D014633:Valine / Q000096:biosynthesis
D000597:Amino Acids, Branched-Chain; D002250:Carbon Radioisotopes; D004800:Enzymes, Immobilized; D009590:Nitrogen Radioisotopes; D005969:Glutamate Dehydrogenase; D000637:Transaminases; D007930:Leucine; D014633:Valine