The roles of synthesis and degradation in determining tissue concentrations of lactate dehydrogenase-5.
C(14)-labeled amino acids were incorporated in vivo into LDH-5 of rat tissues. Different amounts of LDH-5 in liver, heart muscle, and skeletal muscle resulted from differences in rates of both intracellular degradation and synthesis. Rate constants for LDH-5 synthesis were 65, 2, and 5 picomoles per day per gram in rat liver, heart muscle, and skeletal muscle, respectively; rate constants for degradation were 0.041, 0.399, and 0.018 reciprocal days, respectively. The corresponding half-lives for LDH-5 in these tissues were 16, 1.6, and 31 days. Markedly divergent rates of LDH-5 catabolism in various tissues suggest the possibility that one isozyme with a slow rate of destruction may serve to maintain critical enzymatic activity in a tissue where rapid degradation of another isozyme occurs.
D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D002247:Carbon Isotopes; D007527:Isoenzymes; D007770:L-Lactate Dehydrogenase / Q000096:biosynthesis / Q000378:metabolism*; D008099:Liver / Q000201:enzymology*; D009132:Muscles / Q000201:enzymology*; D009206:Myocardium / Q000201:enzymology*; D014176:Protein Biosynthesis; D011506:Proteins / Q000378:metabolism*; D051381:Rats
D000596:Amino Acids; D002247:Carbon Isotopes; D007527:Isoenzymes; D011506:Proteins; D007770:L-Lactate Dehydrogenase