Inhibitors of Tyrosinase

1955 ◽  
Vol 32 (3) ◽  
pp. 468-484
Author(s):  
M. G. M. PRYOR
Keyword(s):  
Methylene Blue ◽  
Dissolved Oxygen ◽  
Inhibitory Effect ◽  
Tyrosinase Activity ◽  
Aromatic Substrate ◽  
Oxidation Reduction ◽  
Oxidation Reduction Potential ◽  
Low Concentrations ◽  
Sulphydryl Groups

1. It has been reported that if Drosophila larvae are ground to a fine paste with sand, the homogenate shows little tyrosinase activity, but that if the larvae are allowed to blacken in chloroform vapour before grinding, activity is increased. 2. This has been interpreted as showing the effect of an intracellular inhibitor, set free by rupturing the cells, but destroyed by chloroform. This inhibitor has been identified by previous authors as a dehydrogenase. 3. It is here suggested that the lack of activity of Drosophila extracts prepared with sand is due to destruction of tyrosinase as it oxidizes naturally occurring aromatic substrates. 4. It is shown that tyrosinase is destroyed by oxidizing the aromatic substrate present in the cuticle of Calliphora larvae, or by very low concentrations of homocatechol. 5. The aromatic substrate of Calliphora larvae is concentrated in the cuticle, and would be set free by fine grinding. 6. Drosophila or Calliphora larvae yield a more active extract when ground with sand than when simply crushed, provided that they are tested soon after grinding. 7. The tyrosinase activity of such extracts is not increased by chloroform or methanol. 8. The compound between o-quinones and amino-acids is capable of oxidizing ascorbic acid or excess amino-acid without the aid of an enzyme, and of simultaneously reducing methylene blue. 9. This reaction, rather than the activity of dehydrogenases, is probably responsible for most of the ability of damaged insect tissue to bleach methylene blue. 10. The blood of insects normally contains dissolved oxygen in equilibrium with the air. 11. The reaction involved in the blackening of insect blood may consume all the dissolved oxygen. 12. Previous observations on fluctuations in the oxidation-reduction potential of the blood of Calliphora larvae with age are probably due to changes in the rate at which oxygen is consumed by the blood after it is shed. 13. There does not therefore appear to be any valid evidence that tyrosinase is inhibited in vivo by the action of dehydrogenases. The absence of tyrosinase activity in undamaged tissue is probably due to the structure of the cytoplasm, which keeps enzyme and substrate apart. 14. Instances of the inhibition of tyrosinase reported in Crustacea and Echinodermata seem to be susceptible of the same explanation as in insects. 15. The supposed inhibitory effect of sulphydryl groups reported for vertebrate melanophores is shown to be due to the combination of sulphydryl groups with o-quinones, which prevents the formation of melanins.

Influence of dissolved oxygen and oxidation–reduction potential on the denitrification rate of activated sludge

1994 ◽  
Vol 30 (6) ◽  
pp. 91-100 ◽  
Author(s):  
Ewa Lie ◽  
Thomas Welander
Keyword(s):  
Dissolved Oxygen ◽  
Activated Sludge ◽  
Reduction Potential ◽  
Inhibitory Effect ◽  
Denitrification Rate ◽  
Oxidation Reduction ◽  
Oxidation Reduction Potential ◽  
Low Concentrations ◽  
Denitrification Activity ◽  
Do Concentration

The influence of low concentrations of dissolved oxygen (DO) and the oxidation-reduction potential (ORP) on the denitrification activity of activated sludge has been studied in batchwise experiments. The ORP was maintained at different levels by automatic titration with air and the denitrification activity was determined by following the disappearance of nitrate. Oxygen was found to have a negative effect on denitrification even at lower concentrations than can be measured with conventional oxygen probes (<0.1 mg/L). The ORP was found to be a useful indicator of the DO concentration at this low level and the denitrification rate was found to decrease linearly with increasing ORP. However, the effect of the ORP on denitrification differed between sludges from different treatment plants. A linear relationship was also found between the ORP and the DO concentration in the region of measurable DO concentrations. Extrapolation of this straight line into the region where DO was under the detection limit indicated that oxygen exerts an inhibitory effect on denitrification at such low concentrations as a few μg/L.

scholarly journals A study of an insect cuticle: the formation of the puparium of Sarcophaga falculata Pand. (Diptera)

1947 ◽  
Vol 134 (874) ◽  
pp. 79-110 ◽  
Keyword(s):  
Methylene Blue ◽  
Reduction Potential ◽  
Reducing Power ◽  
Tyrosinase Activity ◽  
Enzymatic Oxidation ◽  
Insect Cuticle ◽  
Potentiometric Studies ◽  
Mature Larva ◽  
Oxidation Reduction ◽  
Oxidation Reduction Potential

The structural and chemical changes taking place in the cuticle of the mature larva of Sarcophaga as it is converted into the puparium are fully described. The formation of the hard and dark exocuticle of the puparium from the outer endocuticle of the larva is due, as Pryor (1940 b ) has shown, to the action of a phenol derived from the blood, a polyphenol oxidase located in the inner epicuticle and present considerably before pupation being responsible for the rapid oxidation of the phenol. The blood phenol, although spontaneously oxidizable, passes unchanged through the inner endocuticle which remains soft and white, and this may be correlated with the ability of the inner endocuticle to reduce methylene blue. The phenol hardening the puparium is produced in the blood by the enzymatic oxidation of tyrosine. Tyrosine in the blood increases steadily in amount before pupation, and during this period the enzyme tyrosinase also appears and increases. The source of tyrosinase appears to lie in the oenocytoids of the blood, which increase in number as the larva matures and die away shortly before pupation. But although tyrosine and tyrosinase are present together in the blood of the mature larva, inhibiting conditions prevent the activity of the enzyme until very shortly before pupation. Tyrosinase activity, however, may be experimentally stimulated before pupation by the action of methyl alcohol and more slowly by narcotics, and it is speculated that the inhibition of tyrosinase in the mature larva may perhaps be effected by the activity of a further enzyme, a dehydrogenase, which operates by increasing the reducing power of the blood. Colorimetric and potentiometric studies of the reducing power of the blood have been carried out, and it has been found that the oxidation-reduction potential of the blood decreases steadily as the larva matures, and then rises sharply just before pupation. The coincidence of this rise with the period of liberation of the pupation hormone suggests that one function of the hormone is to destroy the reducing power of the blood, so liberating tyrosinase activity and leading to the production of a polyphenol which passes into and hardens the cuticle. In conclusion, it is suggested that the homology between the insect and crustacean cuticles is closer than has been hitherto emphasized.

scholarly journals Studies on Analogues of L-Cysteine and L-Cystine

Blood ◽  
1956 ◽  
Vol 11 (1) ◽  
pp. 1-10 ◽  
Author(s):  
AUSTIN S. WEISBERGER ◽  
LEIF G. SUHRLAND ◽  
JOSEPH SEIFTER
Keyword(s):  
Amino Acids ◽  
Spatial Configuration ◽  
Spatial Relationship ◽  
Inhibitory Effect ◽  
Selenium Compounds ◽  
Low Concentrations ◽  
Relationship Of ◽  
Normal Cellular Function

Abstract The amino acids L-cysteine and L-cystine appear to have an important role in the metabolism of leukocytes. Decreased availability of these amino acids may therefore have important effects on leukocytes. The possibility of decreasing the influx of radioactive L-cystine into leukemic leukocytes was investigated by exposing the leukocytes to various analogues of cysteine (cystine) prior to incubation with S35 L-cystine. It was found that a highly specific structural and spatial configuration is required to decrease the influx of S35 L-cystine. Thus unlabeled L-cysteine is effective in decreasing the incorporation of radioactive L-cystine. However, analogues of cystine in which there is modification or substitution of the sulfhydryl, amino or carboxyl group do not decrease the influx of S35 L-cystine. Furthermore, any alteration in the spatial relationship of the sulfhydryl and amino groups of L-cysteine also results in a loss of the ability of an analogue to decrease the incorporation of S35 L-cystine. Of the compounds studied and in the concentrations employed, only unlabeled L-cysteine, selenium cystine and phenyl selenium cysteine were effective. Selenium cystine is identical with cystine except that selenium replaces the sulfur in the molecule. Phenyl selenium cysteine is also closely related structurally to cysteine. The mechanism of action of selenium cystine and phenyl selenium cysteine in decreasing the influx of S35 L-cystine is not known. Other selenium compounds tested were ineffective. These compounds may exert their inhibitory effect by (a) competitive combination with specific intracellular receptors for L-cysteine (L-cystine), (b) inactivation of enzymes or compounds essential for normal cellular function, (c) alteration in membrane permeability or (d) a toxic effect of selenium. Since selenium cystine and phenyl selenium cystine are inhibitory in low concentrations in vitro, these compounds may have important effects on leukemic leukocytes in vivo.

Experimental considerations on monitoring ORP, pH, conductivity and dissolved oxygen in nitrogen and phosphorus biological removal processes

2001 ◽  
Vol 43 (11) ◽  
pp. 197-204 ◽  
Author(s):  
A. Spagni ◽  
J. Buday ◽  
P. Ratini ◽  
G. Bortone
Keyword(s):  
Dissolved Oxygen ◽  
P Uptake ◽  
Biological Nutrient Removal ◽  
Effective Control ◽  
Monitoring And Control ◽  
Nitrogen And Phosphorus ◽  
Ph Variation ◽  
Oxidation Reduction ◽  
Oxidation Reduction Potential ◽  
Removal Processes

An experimental study on monitoring Oxidation Reduction Potential (ORP), pH, Conductivity and Dissolved Oxygen (DO) in an Enhanced Biological Nutrient Removal process has been carried out. In the anaerobic phase, while ORP and conductivity were not reliable in monitoring simultaneously denitrification and P-release, pH showed the best performances. A significant relationship between P-released and pH variation was found. During the aerobic phase both ORP and pH were able to monitor successfully the nitrification, even though pH was much more reliable. pH can be also used for monitoring and control enhanced P-uptake. It has been concluded that, for a reliable and effective control of biological N and P removal processes a more sophisticated control system seems to be necessary.

Prospective evaluation of uterine receptivity in mice

2018 ◽  
Vol 30 (4) ◽  
pp. 619 ◽  
Author(s):  
Hitomi Nakamura ◽  
Takayoshi Hosono ◽  
Keiichi Kumasawa ◽  
Tadashi Kimura
Keyword(s):  
Roc Curve ◽  
Implantation Failure ◽  
Uterine Receptivity ◽  
Roc Curve Analysis ◽  
Failure Group ◽  
Uterine Endometrium ◽  
Oxidation Reduction ◽  
Oxidation Reduction Potential ◽  
And Control

In current infertility treatments it is necessary to evaluate uterine receptivity in each menstrual cycle. During the implantation period, the uterus goes through many complex orchestrated changes, including changes to the glycocalyx. The changes to the glycocalyx are due to sialylation, sulfation and fucosylation. Can the measurement of in-vivo uterine pH and/or oxidation-reduction potential (ORP) determine the alterations of uterine endometrium for implantation and evaluate prospective uterine receptivity? In the present study we assessed in vivo uterine pH and ORP during the early stages of pregnancy in naïve mice, as well as in a murine model of implantation failure created by local and transient suppression of signal transducer and activator of transcription 3. There was no change in the in vivo uterine pH between post-coitus Days 2 and 6. In vivo uterine ORP was significantly higher compared to the day before. One day before implantation began, uterine ORP was significantly decreased in the implantation failure group compared with the naïve and control groups. Receiver operator characteristic (ROC) curve analysis of uterine ORP as a predictor of non-conception showed an area under the ROC curve of 0.96 (95% confidence interval 0.92–1.00). Thus, in vivo uterine ORP could be a parameter to prospectively evaluate uterine receptivity.

Apparatus and techniques for the measurement of oxidation-reduction potentials, pH and oxygen tension in vivo

1957 ◽  
Vol 146 (923) ◽  
pp. 289-297 ◽  
Keyword(s):  
Oxygen Tension ◽  
Reduction Potential ◽  
Model Experiments ◽  
Reduction Potentials ◽  
Oxidation Reduction ◽  
Oxidation Reduction Potential ◽  
Small Voltage

In order to follow the changes which occur in tumours during treatment with radiation, and the effects of radiosensitizing or radioprotecting drugs, apparatus and techniques have been developed to record automatically changes of oxidation-reduction potential on eight different electrodes. Simultaneous records of pH and oxygen tension changes were used as controls in some experiments. The changes of oxygen tension were followed by applying a known small voltage to one electrode and measuring the current which flowed. Calibration of oxygen-tension measurements was attempted by the use of model experiments.

scholarly journals Distribution characteristics of dissolved oxygen and stable isotope compositions of shallow groundwater in the vicinity of an inland nuclear power plant, HK, China

2019 ◽  
Vol 98 ◽  
pp. 09035
Author(s):  
Jinjing Zan ◽  
Yihui Dong ◽  
Weimin Zhang ◽  
Weidong Xu ◽  
Jiale Li ◽  
...  
Keyword(s):  
Power Plant ◽  
Nuclear Power Plant ◽  
Dissolved Oxygen ◽  
Nuclear Power ◽  
Atmospheric Precipitation ◽  
Shallow Groundwater ◽  
Jiangxi Province ◽  
Oxidation Reduction ◽  
Oxidation Reduction Potential ◽  
Hydrogen And Oxygen Isotope

The hydrochemical and stable hydrogen and oxygen isotope compositional characteristics of surface and shallow groundwaters in the vicinity of HK nuclear power plant in Jiangxi Province of China. Dissolved oxygen (DO) contents of shallow groundwaters range between 1.75 to 19.40 mg/L, with variations related to well depth, groundwater level, and oxidation-reduction potential. Respective ranges of δD and δ18O (‰ VSMOW) in shallow groundwaters are -40.7 to -24.9 and -6.71 to -5.40, with average values of -31.8 and -5.87. The δD-δ18O relationship for the study area is δD = 8.3δ18O +16.8, indicating that atmospheric precipitation is the major recharge source of shallow groundwaters.

scholarly journals The hydrogen-ion concentration and the oxidation-reduction potential of the cell-interior: a micro-injection study

1925 ◽  
Vol 98 (689) ◽  
pp. 259-286 ◽  
Keyword(s):  
Methylene Blue ◽  
Gentian Violet ◽  
Reducing Power ◽  
Ion Concentration ◽  
Hydrogen Ion Concentration ◽  
Oxidation Reduction ◽  
Oxidation Reduction Potential ◽  
Living Organisms ◽  
Actual Formation ◽  
Qualitative Estimation

It has been recognised since the middle of the eighteenth century that one of the most fundamental characteristics of living organisms is their capacity to oxidise substances incapable of oxidation at ordinary temperatures; but no qualitative estimation of this power of oxidation was carried out until the time of Ehrlich, whose classical experiments on the injection of methylene blue into the intact animal revealed the fact that certain organs seemed to have a higher reducing power than others. Later, much histo-chemical work was done. Numerous observers studied the effect of staining tissues and cells in reagents which indicated by their colour whether they were reduced or oxidised. Several such indicators were used by the earlier workers, especially alphanaphthol and pyronin and alpha-naphthol and gentian violet; but the two chief methods were the intracellular formation of an indophenol, introduced by Röhmann and Spitzer in 1895 (20), and the oxidation of the leucobase of methylene blue, introduced by Unna in 1911 (23). In the latter case the cell was placed in a solution of the completely reduced dye, and the conclusion was that wherever the blue colour appeared, there the cell had been able to oxidise it. The indophenol method depended on the actual formation and precipitation of a dye in the cell by an oxidative condensation. The original reactants used were dimethylparaphenylenediamine and alpha-naphthol, but various later workers modified this by using other phenols and other aromatic amines, so that indophenols of different colours were produced.

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