Purification and substrate kinetics of plant lactate dehydrogenase

• Published in: Phytochemistry (Oxford) 1997-07, Vol.45 (5), p.889-896
• Main Authors: Mulcahy, Patricia, O'Carra, Padraig
• Format: Article
• Language: English
• Subjects: Analytical, structural and metabolic biochemistry; Biological and medical sciences; Brassica rapa; Compositae; Cruciferae; Enzymes; Enzymes and enzyme inhibitors; Fundamental and applied biological sciences. Psychology; lactatc dehydrogenase affinity purification; Lactuca sativa; lettucc; Metabolism; Oxidoreductases; Plant physiology and development; turnip
• ISSN: 0031-9422; 1873-3700
• DOI: 10.1016/S0031-9422(97)00078-2

Lactate dehydrogenase (LDH) from turnip ( Brassica rapa; Cruciferae), purified to electrophoretic homogeneity using affinity chromatography, has a native M r , of 157 × 1O 3 and a subunit M r , of 38 × 10 3. The LDH from turnip shows the same relative effectiveness (relative V max and K m values) as the mammalian H 4 and M 4 isoenzymes with pyruvate, lactate and glyoxylate (oxoacetate and dihydroxyacetate) as substrates. All three LDH types show no activity with glycolate (hydroxyacetate). The affinities for these and a range of competitive inhibitory analogues shows a consistent pattern of highest affinity for the H 4 mammalian isoenzyme, medium affinity for the M 4 form and lowest affinity for the plant enzyme, in a ratio of about 10:3:1, respectively. The catalytic mechanism of the plant enzyme is very similar to that of the mammalian forms. The major physiological activity of the plant LDH is considered to be pyruvate reduction, rather than the disproportionation of glyoxylate that has been proposed as a plant cell pH-stat. © 1997 Elsevier Science Ltd. All rights reserved