Assuntos
Rim/enzimologia , Fígado/enzimologia , Músculos/enzimologia , Miocárdio/enzimologia , Piruvato Quinase , Envelhecimento , Animais , Animais Recém-Nascidos , Cromatografia DEAE-Celulose , Eletroforese , Feminino , Coração/embriologia , Coração/crescimento & desenvolvimento , Isoenzimas , Rim/crescimento & desenvolvimento , Fígado/embriologia , Fígado/crescimento & desenvolvimento , Masculino , Desenvolvimento Muscular , Músculos/embriologia , Testes de Precipitina , Gravidez , Coelhos/imunologia , Ratos , DesmameRESUMO
In the report "Lactate dehydrogenase isozymes: Further kinetic studies at high enzyme concentration" by Thomas Wuntsch, Raymond F. Chen, and Elliot S. Vesell [169, 480 (1970)], 14.0 mM NAD in line 2 of the heading of Table 1 should read 14.0 , microM NAD.
RESUMO
By competition with lactate dehydrogenase (LDH) for nicotinamide adenine dinucleotide (NAD), commonly occurring intracellular proteins, such as glyceraldehyde-3-phosphate dehydrogenase, malate dehydrogenase, and albumin, can protect LDH-1 and LDH-5 from inhibition and ternary complex formation with NAD and pyruvate. The existence of intracellular proteins that compete with LDH for NAD renders unphysiological a model for estimating the extent of intracellular LDH inhibition based on incubations of only LDH, NAD, and pyruvate.
Assuntos
L-Lactato Desidrogenase/antagonistas & inibidores , NAD , Piruvatos , Gliceraldeído-3-Fosfato Desidrogenases , Isoenzimas , Cinética , Malato Desidrogenase , Modelos Químicos , Soroalbumina BovinaRESUMO
The kinetic properties of lactate dehydrogenase (LDH) isozymes have been determined at high enzyme concentrations. Spectrophotofluorometric assays revealed that the extent of substrate inhibition of LDH-1 and LDH-5 depends on enzyme concentration. At high enzyme concentrations, in the range of those that exist in most mammalian cells, no inhibition by pyruvate occurred. Pyruvate concentrations up to and including 20.0 millimoles per liter were used for each isozyme at 25 degrees and 40 degrees C at pH 7.0 and 7.4. These results suggest that substrate inhibition of LDH may not occur in vivo but only in vitro after appreciable dilution from physiologic enzyme concentrations. These experiments provide further evidence against the theory that substrate inhibition of LDH-1 in vivo accounts for the distribution of LDH isozymes within various tissues. They raise the possibility that, for other enzymes, kinetic properties determined at highly dilute concentrations in vitro may also be quite different from kinetic properties at the much higher concentrations that exist in vivo.
