Influence of Salts on Activity of Malic Dehydrogenase from Spinach Leaves

Abstract

It is well established (10,18,19) that the respiratory rates of plant tissues containing low concentrations of salts are markedly stimulated by adding to the bathing medium any one of a variety of salts. In view of this fact and of the limited information available on the biochemical role of certain essential mineral ions in metabolism it seems that any detailed information concerning the influence of the ionic environnient onl the activities of important respiratory or other plant enzymes may be of considerable physiological interest.There is considerable information in the literature indicating effects of the ionic environment on the activity of both particulate and soluble enzyme preparations. It has been reported (13) that inorganic salts of both univalent and divalent cations markedly stimulatedl the activity of particulate cytochrome oxidase. Honda et al (6) have shown that the rate of oxidation of reduced diphosphopyridine nucleotide (DPNH) catalyzed by Nwashed mitochondria from beet root (Beta vulgaris L.) was increased by adding certain salts to the assay medium. The activity of glucose-6-phosphate dehydrogenase was reported to be increased as nmuch as six-fold by low concentrations of certain anions (20). The ionic environment markedly affected the Michaelis constant (K,,) of this enzynie with respect to both glucose-6-phosphate and TPN. Massey (12) reported that sulfate, selenate, arsenite, citrate, borate, phosphate, and arsenate, in increasing order of effectiveness, activated salt-free fumarase and altered the pH of optimal activity while chloridle, bromide, thiocyanate, and iodide in increasing or(ler of effectiveness, inhibited the activity of this enzyme. The extent of inhibition was markedlly dependent on pH. Zelitch (29) has reported that the rate of reduction of hydroxypyruvate as catalyzed by crystalline glyoxylic acid reductase was markedly increased by various anions and that the magnitude of activation was not the same at different pH levels. Eichel (5) reported that DPNH oxidase activity of cell-free homogenates of Tetrahvmnena pvriform,wis was increased two-to three-fold when phosphate was used with tris(hydroxymethyl)aminomethane (Tris) buffer. Other compounds such as KCI, NaCl, K.S04, or Na.,HAsO4 replaced phosphate in systems buffered with Tris.

Changes in Levels of Nicotinamide Adenine Nucleotides and Krebs Cycle Intermediates in Mung Bean Leaves after Illumination

“…Much of the 140 from this source could accumulate in citrate through the change in NADjNADH2 limiting the rate of isocitric .dehydrogenase (NAD-mediated) in the direction of decarboxylation. However, it is not clear why the 14 0 from aspartate should appear in citrate rather than in malate during the first phase, since the similarity of the relevant kinetic constants (Hiatt and Evans 1960;Hiatt 1962) argues against disparate competition between malic dehydrogenase and condensing enzyme for the available oxaloacetate.…”

The Effect of Salinity on the Malic Dehydrogenase of Pea Roots

“…Laxton progress) were grown on vermiculite moistened with Hoagland solution and salinated witlh NaCl or Na2SO4 at concentration of 1 to 5 atm as previously described (12,13 Change.i in the amounit of acids in the cell, in response to the salinity of the medium, may affect the level of the enzymes connected with the metabolism; of these acids. Many investigators (2,4,18), therefore, lhave looked for the effect of salinity on malate dehydrogenase activity. Most of them, however, dealt with the effect of salt present in the assay mixture, on the enzyme activity.…”

“…Hiatt and Evans (4) investigated the effect of salt on the enzyme activity in a whole range of pH. They found the same response of the enzyme to different salts of the same concentration.…”

An Apparent Oligomer of Malate Dehydrogenase from Bean Leaves

“…The total activity recovered following both salt treatments increased, however. This may be due partially to changes in volume during dialysis or activating effects of sodium and other univalent ions or both (17,20,53). During centrifugation, the protein was moved from its NaCl environment into the sucrose density gradient medium.…”