T. Lee
Jul 1, 1966
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0
Influential Citations
1
Citations
Journal
Physiologia Plantarum
Abstract
Hydroxyhenzoic acids were tested for their effects on oxidation of the reduced nicotinamide adenine dinucleotide (NADH) in the absence of added H2O2 and Mn2* by an enzyme preparation from tobacco leaves (Nicotiana tabacum, var. White Gold). For comparison, a commercial horseradish peroxidase was also used. The rate of NADH oxidation was followed spectruphotometrically at 340 nm. Mono- and dihydroxybenzoic acids exerted significant effect on the rate of NADU oxidation, yet their effectiveness was determined by the number and position of the hydroxyl group on the ring. 4-Hydroxybenzoic acid was very effective in stimulating the reaction. Shifting the hydroxyl from the 4- to the 3-position and from the 3- to the 2-position decreased activity. 2,4- And 2,5-dihydroxybenzoic aeids were more active than the other dihydroxy-iscuners in stinulating oxidation of NADH. the dihydroxybenzoic acids with the hydroxyls in adjacent positions were less effective, and their activity was affected by other phenolic activators. In the presence of 4-hydroxybenzoic acid which enhanced oxidation of NADH, 2,4- and 2,5-dihydroxybenzoic acids further stimulated the reaction, but 3,4-, 2,3- and 2,6-dibydoxybenzoic acids were inhibitory. The inhibition by 3,4- and 2,3-dihydroxybenzoic aciils was non-competitive. The enzymes extracted by a L-cysteine-containing buffer showed lower NADH-oxidase activity. The enzyme preparation possessed peroxidase activity. The activity of NADH-oxidase inereased when H2O2 and Mi2* were present in addition to 4-hydroxy-benzoic acid. The effect of the position and number of hydroxyl substitution on the rate of NADH oxidation by borseradish peroxidase was also significant. This suggests the involvement of peroxidase in the NADH-oxidase system of tobacco leaves. However, a combination of the inactivated enzyme solution and active horseradish peroxidase with peroxidase activity equivalent to that of the enzyme preparation from tobacco leaves did not reconstitute the NADH-oxidase activity of tobacco leaves. This and other evidence suggests that the soluble NADH-oxidizing zyme system of tobacco leaves is more complicated than peroxidase.