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Biomedical subjects

S F Yang

Publications and source records attributed to S F Yang.

At least 127 records · Page 7Linked to original sources
PubMed1975

Inhibition of in Vivo Conversion of Methionine to Ethylene by l-Canaline and 2,4-Dinitrophenol.

l-Canaline, a potent inhibitor of pyridoxal phosphate-mediated reactions, markedly inhibited the conversion of methionine to ethylene and carbon dioxide by apple tissue. A 50% inhibition of methionine conversion into ethylene was obtained with 50 mum canaline and almost complete inhibition with 300 mum canaline. When 2,4-dinitrophenol, an oxidative phosphorylation uncoupler, was fed to apple tissue, it inhibited the conversion of radioactive methionine to ethylene by 50% at a concentration of 60 mum and by 90% at a concentration of 100 mum. Production of labeled carbon dioxide from acetate-1-(14)C was increased by 2,4-dinitrophenol, indicating that the inhibition of ethylene production was due to uncoupling of phosphorylation. Auxin-induced ethylene production by mungbean (Phaseolus mungo L.) hypocotyl sections was similarly inhibited by these inhibitors.These results support the proposal that pyridoxal phosphate is involved in the formation of ethylene from methionine, substantiate the requirement for ATP in ethylene production, and suggest that this ATP requirement occurs in the step (s) between methionine and ethylene. The biosynthetic mechanism probably involves activation of methionine by ATP followed by a pyridoxal phosphate-mediated gamma-elimination.

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PubMed1975

Interaction of kinetin and calcium in relation to their effect on stimulation of ethylene production.

Application of kinetin and Ca(2+) caused a striking synergistic increase in ethylene production by mung bean (Phaseolus aureus Roxb) hypocotyl segments. The effect of kinetin on Ca(2+) uptake and of Ca(2+) on the uptake and metabolism of kinetin in relation to their effect on ethylene production was studied. Tracer experiments showed that kinetin greatly increased the uptake of (45)Ca(2+) after 6 hours of incubation. Reciprocally, Ca(2+) stimulated the uptake of kinetin-8-(14)C and remarkably enhanced the metabolism of kinetin-8-(14)C into several polar metabolites. Consequently, the quantity of free kinetin-8-(14)C remaining in Ca(2+)-treated segments was much less than in control segments. A possible mechanism accounting for the synergism between kinetin and calcium on ethylene production is discussed.

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PubMed1974

Phosphoenolpyruvate carboxylase from spinach leaf tissue: inhibition by sulfite ion.

Phosphoenolpyruvate carboxylase (EC 4.1.1.31), partially purified from spinach (Spinacia oleracea) leaves, is inhibited by SO(3) (2-) ion. The inhibition is competitive or mixed type with respect to HCO(3) (-) (Ki = 17 mm), and noncompetitive with respect to phosphoenolpyruvic acid (Ki = 11 mm), Mg(2+) (Ki = 10 mm), and Mn(2+) (Ki = 2.4 mm). The inhibitory effect of SO(3) (2-) is more significant in the presence of Mn(2+) than in the presence of Mg(2+). l-Malate, an inhibitor of phosphoenolpyruvate carboxylase activity, and SO(3) (2-) may bind at the same site on the enzyme. Glyoxal bisulfite and glyoxylate bisulfite are equally effective inhibitors of the enzyme activity as SO(3) (2-), but alpha-hydroxypyridinemethanesulfonate is a weak inhibitor. The data are discussed in relation to the physiological effect of the air pollutant (SO(2)) on plant leaf metabolism.

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PubMed1974

Effect of 2,4-Dinitrophenol on Auxin-induced Ethylene Production and Auxin Conjugation by Mung Bean Tissue.

Auxin-induced ethylene production by mung bean (Phaseolus mungo L.) hypocotyl segments was markedly inhibited by 2,4-dinitrophenol regardless of whether or not kinetin was present. Uptake of indoleacetic acid-2-(14)C was also inhibited in the presence of 2,4-dinitrophenol. Segments treated only with indoleacetic acid rapidly converted indoleacetic acid into indole-3-acetylaspartic acid with time whereas kinetin suppressed indoleacetic acid conjugation. Formation of indole-3-acetylaspartic acid was significantly reduced when 2,4-dinitrophenol was present. The suppression of indoleacetic acid conjugation by kinetin and 2,4-dinitrophenol appeared to be additive, and the free indoleacetic acid level in segments treated with 2,4-dinitrophenol in the presence of indoleacetic acid or indoleacetic acid plus kinetin was remarkably higher than in corresponding segments which received no 2,4-dinitrophenol.In the absence of 2,4-dinitrophenol, indoleacetic acid-induced ethylene parallels the free indoleacetic acid level within the tissue. However, in the presence of 2,4-dinitrophenol the rate of ethylene production did not correlate with the free indoleacetic acid level. These results indicate that both indoleacetic acid-induced ethylene production and indoleacetic acid conjugation require a continuous supply of ATP, the formation of which was inhibited by 2,4-dinitrophenol.

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PubMed1973

Mechanism of a Synergistic Effect of Kinetin on Auxin-induced Ethylene Production: Suppression of Auxin Conjugation.

In hypocotyl segments of mung bean (Phaseolus mungo L.) seedlings, exogenously supplied indoleacetic acid was rapidly conjugated mainly into indoleacetylaspartic acid, which was inactive in inducing ethylene production. Kinetin is known to stimulate indoleacetic acid-induced ethylene production. The mechanism of kinetin action on indoleacetic acid-induced ethylene production by hypocotyl segments of mung bean seedlings was studied in relation to indoleacetic acid uptake and indoleacetic acid metabolism. Kinetin enhanced indoleacetic acid uptake during the initial 2-hour incubation and markedly suppressed the conversion of indoleacetic acid to indoleacetic acid conjugates throughout the whole 7-hour incubation. As a result, there was more free indoleacetic acid and less conjugated indoleacetic acid in the segments treated with kinetin than in those receiving no kinetin. A close relationship was demonstrated between the rate of ethylene production and the level of free indoleacetic acid, which was regulated by kinetin.

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PubMed1971

Ethylene biosynthesis in fruit tissues.

Tracer studies with avocado tissues indicate that methionine is converted to ethylene at stages of the climacteric rise and the climacteric peak, but not at the preclimacteric stage. The results suggest that the control of ethylene biosynthesis is at a step after methionine is synthesized. The endogenous content of methionine was found to be so low that methionine must be actively turned over for ethylene biosynthesis during the stages when the rate of ethylene production is high. Oxygen was found to be essential for this conversion, indicating that at least one of the steps in conversion of methionine to ethylene is oxygen-dependent. The ability of methionine and its keto analogue (alpha-keto-gamma-methylthiobutyric acid) to serve as ethylene precursors by apple tissues was compared. Chemical and kinetic evidence support the view that methionine is a closer precursor of ethylene than its keto analogue.

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PubMed1971

Ethylene-enhanced Synthesis of Phenylalanine Ammonia-Lyase in Pea Seedlings.

The effect of ethylene on the development of phenylalanine ammonia-lyase activity in segments excised from the epicotyl apex of pea seedling was studied. Although there was some increase in phenylalanine ammonia-lyase activity in segments not treated with ethylene, a marked increase in phenylalanine ammonia-lyase activity occurred in ethylene-treated tissues during the incubation. The induction period was estimated to be about 6 hours. The activity reached a maxmum at 30 hours and then declined. On withdrawal of ethylene, the increase was sustained for a short period and then stopped. After retreatment with ethylene, the increase was resumed. Addition of CO(2) reduced the effect of ethylene. Administration of cycloheximide or actinomycin D at an early period almost completely suppressed the increase in phenylalanine ammonia-lyase activity. However, if these inhibitors were administered at a later period, while phenylalanine ammonia-lyase activity was approaching a maximum, they not only failed to reduce but rather stimulated the activity. These results are consistent with the view that there exist both phenylalanine ammonia-lyase-synthesizing and -inactivating systems, and that the development of both systems may involve de novo synthesis of protein.

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PubMed1969

Ethylene production from propanal.

Tracer studies using a model system consisting of Cu(2+) and ascorbate indicate that carbons 2 and 3 of propanal are converted to ethylene, and carbon 1 is converted to formic acid and CO(2). A mechanism accounting for this reaction is described. In apple tissue, methionine but not propanal is readily incorporated into ethylene. It is therefore concluded that propanal is not a precursor of ethylene in this fruit.

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