scholarly journals Oxidation of monohydric phenol substrates by tyrosinase. An oximetric study

1992 ◽  
Vol 288 (1) ◽  
pp. 63-67 ◽  
Author(s):  
S Naish-Byfield ◽  
P A Riley
Keyword(s):  
Oxygen Consumption ◽  
Maximum Rate ◽  
Low Ph ◽  
Molar Ratio ◽  
Lag Phase ◽  
Complete Oxidation ◽  
Mushroom Tyrosinase ◽  
Tyrosine Oxidation ◽  
Rate Of Reaction ◽  
Dopa Oxidase

The purity of commercially available mushroom tyrosinase was investigated by non-denaturing PAGE. Most of the protein in the preparation migrated as a single band under these conditions. This band contained both tyrosinase and dopa oxidase activity. No other activity of either classification was found in the preparation. Oxygen consumption by tyrosinase during oxidation of the monohydric phenol substrates tyrosine and 4-hydroxyanisole (4HA) was monitored by oximetry in order to determine the stoichiometry of the reactions. For complete oxidation, the molar ratio of oxygen: 4HA was 1:1. Under identical conditions, oxidation of tyrosine required 1.5 mol of oxygen/mol of tyrosine. The additional oxygen uptake during tyrosine oxidation is due to the internal cyclization of dopaquinone to form cyclodopa, which undergoes a redox reaction with dopaquinone to form dopachrome and dopa, which is then oxidized by the enzyme, leading to an additional 0.5 mol of oxygen/mol of original substrate. Oxygen consumption for complete oxidation of 200 nmol of 4HA was constant over a range of concentrations of tyrosinase of 33-330 units/ml of substrate. The maximum rate of reaction was directly proportional to the concentration of tyrosinase, whereas the length of the lag phase decreased non-linearly with increasing tyrosinase concentration. Activation of the enzyme by exposure to citrate was not seen, nor was the lag phase abolished by exposure of the enzyme to low pH. Michaelis-Menten analysis of tyrosinase in which the lag phase is abolished by pre-exposure of the enzyme to a low concentration of dithiothreitol gave Km values for tyrosine and 4HA of 153 and 20 microM respectively.

scholarly journals Esterification of palmitic acid with epichlorohydrin on anion exchange resin catalyst

2007 ◽  
Vol 5 (3) ◽  
pp. 715-726 ◽  
Author(s):  
Emil Muresan ◽  
Spiridon Oprea ◽  
Theodor Malutan ◽  
Mihai Vata
Keyword(s):  
Palmitic Acid ◽  
Exchange Resin ◽  
Catalyst Particle ◽  
Molar Ratio ◽  
Catalyst Loading ◽  
Esterification Reaction ◽  
Macroporous Resin ◽  
Resin Catalyst ◽  
Catalyst Particle Size ◽  
Rate Of Reaction

AbstractThe esterification reaction of palmitic acid with epichlorohydrin catalyzed by an anionic macroporous resin was studied. Purolite A-500 resin proved to be a very effective catalyst in the synthesis of 3-chloro-2-hydroxypropyl palmitate. The effects of certain parameters such as speed of agitation, catalyst particle size, catalyst loading, temperature, initial molar ratio between reactants on the rate of reaction were studied. It was found that the overall rate is intrinsically kinetically controlled. The structure of synthesized ester was confirmed by FTIR and 1H NMR analyses.

Oxyresveratrol as the Potent Inhibitor on Dopa Oxidase Activity of Mushroom Tyrosinase

1998 ◽  
Vol 243 (3) ◽  
pp. 801-803 ◽  
Author(s):  
Nam-Ho Shin ◽  
Shi Yong Ryu ◽  
Eun Ju Choi ◽  
Seh-Hoon Kang ◽  
IL-Moo Chang ◽  
...  
Keyword(s):  
Oxidase Activity ◽  
Potent Inhibitor ◽  
Mushroom Tyrosinase ◽  
Dopa Oxidase

Potent Inhibitory Effects of N-Aryl S-Alkylthiocarbamate Derivatives on the Dopa Oxidase Activity of Mushroom Tyrosinase

2005 ◽  
Vol 53 (7) ◽  
pp. 747-749 ◽  
Author(s):  
Kun Ho Lee ◽  
Mamoru Koketsu ◽  
Sang Yoon Choi ◽  
Kang Jin Lee ◽  
Pyeongjae Lee ◽  
...  
Keyword(s):  
Oxidase Activity ◽  
Mushroom Tyrosinase ◽  
Inhibitory Effects ◽  
Dopa Oxidase

Electrochemical Behavior of Cu2+-Histidine Complexes on a Glassy Carbon Electrode

2011 ◽  
Vol 66 (3) ◽  
pp. 279-288 ◽  
Author(s):  
Yu-Ching Weng ◽  
Tian-Hao Cheng
Keyword(s):  
Glassy Carbon Electrode ◽  
Glassy Carbon ◽  
Electrochemical Behavior ◽  
Rotating Disk ◽  
Low Ph ◽  
Rotating Disk Electrode ◽  
Molar Ratio ◽  
Carbon Electrode ◽  
Oxidation Reactions ◽  
High Ph

The electrochemical behavior of Cu2+-L-histidine complexes on a glassy carbon electrode with various coordination environments in aqueous solution has been investigated. The Cu2+-histidine complexes are more easily reduced and oxidized at low pH (pH = 3 ~ 4) than at high pH (pH = 8 ~ 10). Both reduction and oxidation reactions of the Cu2+-histidine complexes are controlled by mass transfer at medium (pH = 5 ~ 7) and high pH (pH = 8 ~ 10) solutions. Even if the molar ratio of histidine to Cu2+ ions is as high as 100 : 1 at low pH of 4, the complexes are easily reduced to form Cu metal directly on the electrode surface. Glassy carbon rotating disk electrode experiments have shown that the electron transfer of the reduction reaction of the Cu2+-histidine complexes is close to 2.

scholarly journals Effects of oxygen tension and pH on the respiratory burst of human neutrophils

Blood ◽  
1979 ◽  
Vol 53 (6) ◽  
pp. 1133-1139 ◽  
Author(s):  
TG Gabig ◽  
SI Bearman ◽  
BM Babior
Keyword(s):  
Oxygen Consumption ◽  
Oxygen Concentration ◽  
Respiratory Burst ◽  
Low Ph ◽  
Human Neutrophils ◽  
Respiratory Burst Activity ◽  
Similar Dependence ◽  
Activated Neutrophils ◽  
Acidic Conditions ◽  
O2 Production

Abstract The respiratory burst of human neutrophils was measured under conditions of hypoxia and low pH. O2 -- production by neutrophils activated with opsonized zymosan fell slowly as the oxygen concentration declined to 1%, then dropped more sharply, reaching negligible levels at oxygen concentrations less than 0.25%. Production was half maximal at an oxygen concentration of 0.35% (equivalent to approximately 10-microM dissolved oxygen). O2- production by the cell- free O2- -forming system prepared from zymosan-activated neutrophils showed a similar dependence on oxygen concentration. A drop in pH caused decreases in both oxygen consumption and O2-- production by zymosan-treated neutrophils, values at PH 6.0 being 10%--20% of those observed at pH 7.5. Experiments with the cell-free O2-- -forming system suggested that this decline in respiratory burst activity at low pH was due to inefficient activation of the O2-- -forming enzyme under acidic conditions.

The role of formaldehyde in the oxidation of ethylene

1952 ◽  
Vol 212 (1110) ◽  
pp. 291-311 ◽  
Keyword(s):  
Activation Energy ◽  
Ethylene Oxide ◽  
Induction Period ◽  
Maximum Rate ◽  
Reaction Scheme ◽  
Stationary Concentration ◽  
Rate Of Reaction ◽  
A Minor ◽  
Close Parallelism

The oxidation of ethylene at temperatures in the region of 400° C has been studied manometrically and analytically, and compared with the oxidation of formaldehyde under similar conditions. The observations of previous authors have been confirmed and extended with particular reference to the factors controlling the maximum rate of reaction. The oxidation of ethylene is closely dependent on the development of formaldehyde, which shows the behaviour to be expected of an agent for degenerate branching. There is a close parallelism between the variation of the activation energy of the oxidation of ethylene from 25 kcal at 350° C to 53 kcal at 550° C and of formaldehyde from 21 kcal at 350° C to more than 40 kcal at 500° C. Formaldehyde is produced in the oxidation of ethylene and attains a maximum concentration which is proportional to the ethylene pressure and independent of the oxygen pressure. The addition of formaldehyde to the reaction mixture reduces or removes the induction period without affecting the maximum rate of the reaction. Ethylene oxide plays a minor but significant part; it attains a stationary concentration in the reaction but is less effective than formaldehyde in reducing the induction period. A reaction scheme based on that proposed by Axford & Norrish (1948) for the oxidation of formaldehyde has been developed; it accounts satisfactorily for the observed facts.

scholarly journals Effects of Ca2+ and Mg2+ on the activity of pyruvate dehydrogenase phosphate phosphatase within toluene-permeabilized mitochondria

1987 ◽  
Vol 241 (2) ◽  
pp. 371-377 ◽  
Author(s):  
P J Midgley ◽  
G A Rutter ◽  
A P Thomas ◽  
R M Denton
Keyword(s):  
Adipose Tissue ◽  
Small Molecules ◽  
White Adipose Tissue ◽  
Pyruvate Dehydrogenase ◽  
Maximum Rate ◽  
Major Effect ◽  
Lag Phase ◽  
Inhibitory Effects ◽  
Highly Sensitive ◽  
Epididymal White Adipose Tissue

Mitochondria from rat epididymal white adipose tissue were made permeable to small molecules by toluene treatment and were used to investigate the effects of Mg2+ and Ca2+ on the re-activation of pyruvate dehydrogenase phosphate by endogenous phosphatase. Re-activation of fully phosphorylated enzyme after addition of 0.18 mM-Mg2+ showed a marked lag of 5-10 min before a maximum rate of reactivation was achieved. Increasing the Mg2+ concentration to 1.8 mM (near saturating) or the addition of 100 microM-Ca2+ resulted in loss of the lag phase, which was also greatly diminished if pyruvate dehydrogenase was not fully phosphorylated. It is concluded that, within intact mitochondria, phosphatase activity is highly sensitive to the degree of phosphorylation of pyruvate dehydrogenase and that the major effect of Ca2+ may be to overcome the inhibitory effects of sites 2 and 3 on the dephosphorylation of site 1. Apparent K0.5 values for Mg2+ and Ca2+ were determined from the increases in pyruvate dehydrogenase activity observed after 5 min. The K0.5 for Mg2+ was diminished from 0.60 mM at less than 1 nM-Ca2+ to 0.32 mM at 100 microM-Ca2+; at 0.18 mM-Mg2+, the K0.5 for Ca2+ was 0.40 microM. Ca2+ had little or no effect at saturating Mg2+ concentrations. Since effects of Ca2+ are readily observed in intact coupled mitochondria, it follows that Mg2+ concentrations within mitochondria are sub-saturating for pyruvate dehydrogenase phosphate phosphatase and hence less than 0.5 mM.

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