The Ascorbic Acid System as an Agent in Barley Respiration

James, William; Cragg, J. M.

doi:10.1111/j.1469-8137.1943.tb04983.x

Cited by 63 publications

(19 citation statements)

References 22 publications

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“…Two possible terminal metallo-oxidases have been found in barley, ascorbic oxidase by James and Cragg (14) and cytochrome oxidase by Merry and Goddard (23). Studies on the intracellular distribution of various ascorbic oxidases by Mandels (21) and Newcomb (25) indicated that the enzymes are localized at the surface.…”

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Ascorbic Acid Oxidase in Barley Roots

Honda

1955

Plant Physiol.

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Two possible terminal metallo-oxidases have been found in barley, ascorbic oxidase by James and Cragg (14) and cytochrome oxidase by Merry and Goddard (23). Studies on the intracellular distribution of various ascorbic oxidases by Mandels (21) and Newcomb (25) indicated that the enzymes are localized at the surface. Newcomb (25) has shown that in many higher plants ascorbic oxidase is attached to or situated near the cell wall. According to the reviews of Goddard and Meeuse (7) and Goddard and Stafford (8), cytochrome oxidase is localized in the mitochondria. Thus, it may be possible to distinguish between ascorbic oxidase and cytochrome oxidase by their intracellular distribution. However, there are differing views on the intracellular distribution of cytochrome oxidase in higher plants. Lundeg'ardh (18) postulated a coating of cytochrome oxidase on the inner surface of the cell walls and in the tonoplast membrane of wheat roots, while Butler (3) considered that it is localized both in the tonoplast membrane and in the mitochondria. Lundegardh (18) suggested that the peripheral localization facilitates salt respiration and accumulation which have been found associated with the cytochrome system (17,31). An added complicatio.n raised by James (12) Homogenates of the root segments were prepared essentially by the method of Newcomb (25). Cellfree homogenates (25 % w/w) were obtained after grinding the roots for 3 to 5 minutes in either icechilled water or media initially 0.8 M tonicity and adjusted to 0.4 M final exogenous tonicity.Centrifugal fractionations of the homogenates were carried out in a refrigerated centrifuge at 0 to 20 C. The wall fragments were resuspended three times in the appropriate medium and the fragments resedi- Ascorbic oxidase and cytochrome oxidase were assayed by Warburg manometric procedures. Temperature equilibration was carried out for 30 minutes before the assay. Substrates and other reagents were then tipped into the main vessel compartments which contained 0.5 ml enzyme preparation, unless otherwise specified. Concentrations of reagents before and after substrate addition were maintained constant. Exogenous inorganic ions were usually excluded. For example, ascorbate was added as the acid form and not as the sodium or potassium salt. This accounts for the low pH in experiments completed before trishydroxymethyl-amino-methane (Tris.), an organic base, was available. In later experiments sufficient organic base was added to maintain the pH. The final pH values of the assay solutions after the last manometer readings were determined with glasscalomel electrodes.The activities quoted are corrected for non-enzymatic oxidation of substrates as computed from similar treatments either without the enzyme preparations or with heat inactivated preparations. No effects of tonicity on the activity were found. Consequently, precautions were not taken to assay activity under a given tonicity.Preparations of various ages were employed since the homogenate was relatively stable with more than...

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Ascorbic Acid Oxidase in Barley Roots

Honda

1955

Plant Physiol.

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“…Apparently similar systems are under investigation elsewhere (Dr. A. Nason, personal communication and Dr. E. Racker, personal communication). Evidence from manometric experiments with preparations from plants in which substrates for dehydrogenases present in the extracts were oxidised by the ascorbate oxidation system has already indicated that such a linkage exists (5,6,7,12); the present report deals chiefly with some pertinent spectrophotometric data on DPNH oxidation. by 0.5 ml of the extracts, on adding 0.5 ml M/25 ascorbate.…”

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The Oxidation of Reduced Diphosphopyridine Nucleotide by an Ascorbate System from Cucumber.

Beevers¹

1954

Plant Physiol.

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“…It had been considered by Stern and Mirsky (1) in the case of wheat germ nuclei, but ruled out on the ground that evidence was lacking for an accumulation of lactic acid during germination, a result to be expected from the high proportion of nuclear glycolysis. Temporary accumulations of lactic acid in the course of germination have been noted however (4); in germinating seeds therefore, nuclear DPN. H may transfer its hydrogen to pyruvate, the resultant lactic acid being ultimately reoxidized by the cytoplasm.…”

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The Position of the Cell Nucleus in Pathways of Hydrogen Transfer: Cytochrome C, Flavoproteins, Glutathione, and Ascorbic Acid

Stern

Timonen

1954

Journal of General Physiology

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The fact that isolated cell nuclei are capable of metabolizing carbohydrate at least to the stage of pyruvate or of ribose formation (1, 2) may be taken to mean that in the course of their intracellular metabolism nuclei will reduce either the glycolytic coenzyme DPN, or the hexosemonophosphate dehydrogenase coermyme TPN. The intensity of such metabolism being similar in nucleus and cytoplasm, the proportion of total cell coenzyme reduced by the nucleus will vary with its size---some 10 per cent in a liver cell, about 50 per cent in a thymus cell. Since the coenzymes in question are not terminal acceptors of hydrogen but serve only to mediate its transfer, it is a requirement of nuclear metabolism that mechanisms exist whereby reduced nuclear coenzylnes become reoxidized. Little, however, is known about the possibilities of hydrogen transfer in nuclei, and the present communication is therefore addressed to this problem.It is almost certain that nuclei cannot transfer hydrogen to molecular oxygen, a relation unequivocally demonstrated for cytochrome oxidase in rat liver by Hogeboom, Schneider, and Striebich (3). Thus, the ultimate problem of nuclear coenzyme reoxidation--at least for aerobic cells--resolves itself into a search for pathways of hydrogen transfer between nucleus and cytoplasm. No better situation illustrative of this point is to be found than in calf thymus where the nucleus accounts for 60 per cent of total cell mass. Although the nuclei of this tissue are capable of accounting for half the glucose-6-phosphate metabolized (2), it is clear from the data of Table II that the capacity to react with molecular oxygen is entirely restricted to the particles of the peripheral cytoplasm.The restriction of terminal oxidation to autonomous mitochondrial bodies means in effect that the reoxidation of coenzymes, reduced in the course of intermediary carbohydrate metabolism, is a problem common to cytoplasm and nucleus. It will be seen, however, that cytoplasm and nucleus do not share the same mechanisms in response to this common need, even though it is ira-* Present address:

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The Ascorbic Acid System as an Agent in Barley Respiration

Cited by 63 publications

References 22 publications

Ascorbic Acid Oxidase in Barley Roots

Ascorbic Acid Oxidase in Barley Roots

The Oxidation of Reduced Diphosphopyridine Nucleotide by an Ascorbate System from Cucumber.

The Position of the Cell Nucleus in Pathways of Hydrogen Transfer: Cytochrome C, Flavoproteins, Glutathione, and Ascorbic Acid

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