Basis of the stereospecific preference of porcine kidney fibroblasts for D-2-hydroxy-4-methylthiobutanoic acid as a source of methionine.
In previous studies we have found that porcine kidney fibroblasts will grow in medium containing D-2-hydroxy-4-methylthiobutanoic acid (D-methionine hydroxy analogue, D-MHA) as the sole source of methionine but not in medium containing the L-isomer (L-MHA) alone. The fibroblasts have been found to have both D-2-hydroxy acid dehydrogenase (EC 1.1.99.6), which uses D-MHA as substrate (Km = 6.0 mM) and L-2-hydroxy acid oxidase (EC 1.1.3.1), which uses L-MHA as substrate (Km = 7.1 mM). These two activities should make it possible for the fibroblasts to grow on either isomer. Only one protein band with L-2-hydroxy acid oxidase activity can be detected with enzyme-specific staining of protein profiles obtained after polyacrylamide gel electrophoresis. The enzyme L-2-hydroxy acid oxidase from porcine kidney has properties that are different from the two porcine isozymes reported previously by others. Passage of DL-[14C]MHA at tracer levels into the porcine kidney fibroblasts in culture is reduced to 31% of control in the presence of 3.75 mM D-MHA, 86% of control with 3.75 mM L-MHA and 65% with 3.75 mM D-lactate but is not affected by up to 3.75 mM L-lactate. It appears that the transport specificity is the basis for the growth promotion of kidney fibroblasts by the D-isomer of MHA as opposed to L-MHA when each is used as the sole source of methionine.
Schreiner
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CL
Department of Biochemistry, North Carolina State University, Raleigh 27695.
Jones
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EE
D000429:Alcohol Oxidoreductases / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D005347:Fibroblasts / Q000378:metabolism; D007668:Kidney / Q000201:enzymology / Q000378:metabolism*; D007770:L-Lactate Dehydrogenase; D045022:Lactate Dehydrogenases; D008715:Methionine / Q000031:analogs & derivatives* / Q000378:metabolism*; D013237:Stereoisomerism; D013552:Swine
C008391:alpha-hydroxy-gamma-methylmercaptobutyric acid; D008715:Methionine; D000429:Alcohol Oxidoreductases; D045022:Lactate Dehydrogenases; D007770:L-Lactate Dehydrogenase; C071195:D-lactate dehydrogenase; C021380:L-2-hydroxyacid oxidase; C021379:D-2-hydroxyacid dehydrogenase