L-lactate dehydrogenase from leaves of Capsella bursa-pastoris (L.) Med. : I. Identification and partial characterization

Evaluation of the role of lactate dehydrogenase in oxalate synthesis

The kinetic properties of lactate dehydrogenase (LDH) (EC 1.1.1.27) from spinach leaves were studied in order to evaluate the possible roles of LDH in the production of oxalate. LDH was purified by affinity chromatography on affigel blue and oxamate agarose columns. The pH optimum for the reduction of pyruvate was 7.25, while that for the reduction of glyoxylate was 7. The rate of reduction of pyruvate and glyoxylate at the optimum pH indicated substrate inhibition at concentrations above 8 and 40 mM, respectively. The maximum activity of LDH with pyruvate was about three times greater than with glyoxylate. The pH optimum for the oxidation of lactate was 9, with very low activity below pH 8. Substrate inhibition was apparent at lactate concentrations above 10 mM. LDH was inactive with glyoxylate in the oxidative reaction, which would lead to the biosynthesis of oxalate.

Soybean L-(+)-lactate dehydrogenases: purification, characterization, and resolution of subunit structure

Lactate dehydrogenase (LDH) (EC 1.1.1.27) from soybean (Glycine max) was purified 2360-fold to homogeneity using ion-exchange, hydroxyapatite, affinity, and hydrophobic chromatographies. The molecular weight of the holoenzyme is 150,000 +/- 5000. Two-dimensional (isoelectrofocusing-sodium dodecyl sulfate) gel electrophoresis reveals two polypeptides subunits of 5.9 and 6.5 pI and of 36,000 +/- 1000 and 37,000 +/- 1000 Mr, respectively. Nondissociating electrophoresis and isoelectric focusing of LDH resolved five tetrameric isoenzymes with pI's between 6.0 and 6.5. The data suggest that these LDH isoenzymes are derived from random association of the products of two different, but most probably related, genes. Kinetic measurements revealed substrate inhibition at high concentrations of lactic acid and biphasic kinetics with NAD.

The physiological role of the isoenzymes of lactate dehydrogenase in potatoes

Four of the five isoenzymes of lactate dehydrogenase present in potato tubers have been isolated and their kinetic properties examined. The pyruvate-reductase activity of isoenzyme-4 is greatly reduced at low pH, the affinity for both pyruvate and NADH is reduced and ATP has a stronger inhibitory effect. If the design properties of an enzyme dictate a high affinity for substrates, then the Km values for lactate, glyoxylate and NAD are consistent with an oxidative role for isoenzyme-4. The same considerations do not permit a conclusion about the physiological role of isoenzymes-1 to-3. However, an overview of the kinetic properties of these isoenzymes indicates that isoenzyme-1 is best adapted for the role of pyruvate reductase. Consideration of the relationships between kinetic constants and electrophoretic mobilities of the isoenzymes, leads us to predict that isoenzyme-5 is well adapted for a role in the oxidation of lactate or glyoxylate. The lactate dehydrogenase of potato leaves appears to consist prodominantly of an isoenzyme with the same mobility as isoenzyme-2 of the tubers and the two isoenzymes are probably identical. The kinetic properties of this isoenzyme are consistent with roles in either oxidation or reduction.