Joseph H. Bruemmer

Oxidation of geraniol by an enzyme system from orange.

Abstract Enzyme preparations from orange juice vesicles reversibly oxidized geraniol in the presence of NADP. NAD was ineffective for this reaction. The enzyme mediating this reaction—geraniol dehydrogenase (GeDH)—was separated from alcohol dehydrogenase by ammonium sulfate fractionation and gel filtration. GeDH also oxidized nerol, farnesol and citronellol, but at slower rates. Whereas pH9·0 was optimal for geraniol oxidation, geranial was reduced maximally at pH 6·5. Thiol-reacting compounds and metal chelators inhibited GeDH activity. Increasing the ratio of the reduced to oxidized forms of NADP progressively depressed the rate of geraniol oxidation. Thus, in juice cells the redox state of the nucleotide coenzyme may regulate the equilibrium between geraniol and geranial.

Pyruvate metabolism during maturation of hamlin oranges

Abstract The roles of the pyruvate decarboxylation pathway and TCA metabolic cycle in activation of anaerobic metabolism in ripening Hamlin oranges were investigated. Oranges were harvested weekly from October to February during the 1980–81 and 1981–82 growing season. Juice vesicles from each weekly sample were assayed for pyruvate decarboxylase, alcohol dehydrogenase, malic enzyme, phosphoenolpyruvate carboxylase, malate dehydrogenase, citrate synthase, isocitrate dehydrogenase and cytochrome oxidase. Also, juice was assayed for ethanol, acetaldehyde, pyruvate, oxalacetate, malate and citrate. In December when ethanol accumulated rapidly in the fruit, pyruvate decarboxylase and alcohol dehydrogenase increased markedly. During the same month, the pyruvate level declined, suggesting that the increases in enzyme levels activated the conversion of pyruvate to ethanol.

Pyruvate dehydrogenase activity during ripening of hamlin oranges

Abstract Pyruvate dehydrogenase (PD) was examined as a possible regulatory enzyme in the decline in aerobic respiration and increase in anaerobic metabolism in the ripening Hamlin orange. Oranges were harvested weekly over the growing season from October to February. Juice vesicles were excised and analysed for PD and the cofactors, NADH, NAD, ATP and ADP as well as for reduced and oxidized ubiquinone. PD levels increased slightly from October through February. The cofactor ratio of ATP/ADP increased slightly during that period, NADH/NAD increased more than 2-fold and ubiquinone became more reduced. Data suggest that PD could function as a regulatory enzyme in pyruvate metabolism and that either substrate levels of NAD dehydrogenases increased beyond the capacity of the respiratory pathway to adjust to a higher flux, or the oxidative function of the pathway declined over the season.

Sesquiterpene hydrocarbons in processed stored carrot sticks

Abstract The sesquiterpene hydrocarbon composition in processed, stored carrot sticks was studied as part of an investigation on the changes in secondary metabolites that occur during processing and storage of carrots. Carrot sticks were treated by infusion with antimicrobial compounds, antioxidants and cellular constituents and stored in plastic vacuum shrink bags at 2°C for up to three weeks. In each of the five treatments studied, the concentrations of the two major sesquiterpene hydrocarbons, caryophyllene and γ-bisabolene, increased markedly in the second week of storage while the concentrations of these two compounds in control samples decreased moderately during this same period. It appears that the infusion process must stimulate major changes in the sesquiterpene metabolism.

Limonene reductase system in the orange

Abstract (+)-Limonene was reduced to Δ 1 p -menthene by an extract from neutralized orange juice vesicles with either NADPH or NADH. This limonene reductase system was partially purified from the soluble fraction of the extract. Activity was specific for the (+)-form; (−)-limonene was inactive. The enzyme system reduced Δ 8(9) p -menthene more rapidly than (+)-limonene.

Terminal oxidase activity during ripening of hamlin orange

Abstract The terminal oxidase of Hamlin orange was perturbed with the inhibitors potassium cyanide (KCN) and salicylhydroxamic acid (SHAM) to determine functionality of the pathway during ripening. Mitochondrial fractions were prepared from juice vesicles of Hamlin oranges harvested over the maturation season, September to January. The NADH oxidase became more sensitive to KCN and SHAM as the fruit matured. The KCN-insensitive oxidase of mature fruit inhibited by SHAM accounted for about 30% of the total. Oxidation of malate by preparations from December and January fruit was inhibited about 90% by KCN plus SHAM. The fraction of the alternative path which is in actual use by the mitochondria in maturing fruit varied from 0.4 to 0.5 with malate and 0.2 to 0.3 with NADH as substrates.

Regulation of NAD and NADP oxidoreductases in oranges

Abstract Dehydrogenase activity of malate: NAD oxidoreductase in extracts of orange juice vesicles was suppressed by NADH at 5 per cent mole fraction of NAD + . Dehydrogenase activity of alcohol: NAD oxidoreductase in the extract was suppressed by NADH at molar concentration equal to NAD + . Suppressing the reoxidation of reduced NAD by O 2 -linked dehydrogenases in intact fruit increased the mole fraction of reduced NAD in the vesicles. The alcohol content of the juice was increased and the citric acid content of the juice was decreased by the treatment. The increase in ethanol and decrease in citric acid indicates a diversion of pyruvate from citric acid formation to ethanol formation in the fruit.