Cysteine Oxidase Activity Research Articles

Targeting plant cysteine oxidase activity for improved submergence tolerance.

Plant cysteine oxidases (PCOs) are plant O2 -sensing enzymes. They catalyse the O2 -dependent step which initiates the proteasomal degradation of Group VII ethylene response transcription factors (ERF-VIIs) via the N-degron pathway. When submerged, plants experience a reduction in O2 availability; PCO activity therefore decreases and the consequent ERF-VII stabilisation leads to upregulation of hypoxia-responsive genes which enable adaptation to low O2 conditions. Resulting adaptations include entering an anaerobic quiescent state to maintain energy reserves and rapid growth to escape floodwater and allow O2 transport to submerged tissues. Stabilisation of ERF-VIIs has been linked to improved survival post-submergence in Arabidopsis, rice (Oryza sativa) and barley (Hordeum vulgare). Due to climate change and increasing flooding events, there is an interest in manipulating the PCO/ERF-VII interaction as a method of improving yields in flood-intolerant crops. An effective way of achieving this may be through PCO inhibition; however, complete ablation of PCO activity is detrimental to growth and phenotype, likely due to other PCO-mediated roles. Targeting PCOs will therefore require either temporary chemical inhibition or careful engineering of the enzyme structure to manipulate their O2 sensitivity and/or substrate specificity. Sufficient PCO structural and functional information should make this possible, given the potential to engineer site-directed mutagenesis in vivo using CRISPR-mediated base editing. Here, we discuss the knowledge still required for rational manipulation of PCOs to achieve ERF-VII stabilisation without a yield penalty. We also take inspiration from the biocatalysis field to consider how enzyme engineering could be accelerated as a wider strategy to improve plant stress tolerance and productivity.

Persulfide generated from L-cysteine inactivates tyrosine aminotransferase. Requirement for a protein with cysteine oxidase activity and gamma-cystathionase.

Liver cytosols contain factors that produce an inhibitor of tyrosine aminotransferase and other enzymes when incubated with L-cysteine or L-cystine. Cystine-dependent inactivation was caused by cystathionase and required pyridoxal 5'-phosphate, but a second protein was needed to reconstitute cysteine-dependent inactivation. A cytosolic protein was isolated that oxidized free cysteine and brought about inactivation of tyrosine aminotransferase when coincubated with cystathionase. Hematin also oxidized cysteine, which led to cysteine-dependent inactivation of tyrosine aminotransferase in the presence of cystathionase. The inactivation of tyrosine aminotransferase involved three steps: initial oxidation of cysteine to form cystine; desulfuration of cystine catalyzed by cystathionase to form the persulfide, thiocysteine; and reaction of thiocysteine (or products of its decomposition) with proteins to form protein-bound sulfane. Since dithiothreitol reactivated tyrosine aminotransferase, the sulfane probably inactivated the enzyme by oxidation of thiol groups. The present results do not indicate whether the cysteine oxidase activity is enzymatic nor do they prove which form of polysulfide inactivates tyrosine aminotransferase. Reduced glutathione greatly slowed the rates at which sulfane accumulated and at which tyrosine aminotransferase was inactivated. Incubation of DL-cystathionine with liver cytosols led to formation of cysteine, which was oxidized and cleaved to form persulfide, and caused inactivation of tyrosine aminotransferase. Thus, sulfane sulfur that is generated by an enzyme of the transulfuration pathway inactivates a transaminase by nonselective oxidation of enzyme-bound thiol groups.

In vitro study of cysteine oxidase in rat brain

Effects of some cysteine analogs and other compounds on in vitro cysteine oxidase were studied in rat brain microsomes. Among the tested compounds, maximum inhibition of microsomal cysteine oxidase was by alpha,alpha'-dipyridyl and the least inhibition by dithiothreitol. Kinetic and dialysis studies found L-homocysteine to be a competitive and reversible inhibitor of cysteine oxidase. Epinephrine was shown to inhibit cysteine oxidase, whereas pyridoxal HCl activated cysteine oxidase at the same concentration. Except for the Mg2+ ion, other metallic ions inhibited cysteine oxidase activity in the following order: Zn2+ greater than Cu2+ greater than Li+ greater than Ca2+ greater than Co2+ greater than K+ greater than Mn2+. A 12 mM concentration of Mg2+ ion was required to obtain maximum cysteine oxidase activity.

Effect of morphine on cysteine oxidase activity in the brain and reproductive tract of rats

Effect of morphine on cysteine oxidase activity in the brain and reproductive tract of rats

Taurine levels, uptake and synthesizing enzyme activities in degenerated rat retinas

Taurine levels, cysteine oxidase and cysteine sulfinate decarboxylase activities, [ 35S]-taurine uptake in vitro and [ 35S]taurine accumulation in vivo were studied in the retinas of rats in which the inner or the outer cell layers were degenerated by treatment with monosodium glutamate or with iodoacetate-malate respectively. Monosodium glutamate treatment significantly reduced the cysteine oxidase activity to 12% of control and the cysteine sulfinate decarboxylase activity to 34% of control. Taurine levels were unaffected. Taurine accumulation was slightly decreased and taurine uptake in vitro was unchanged by MSG treatment. Iodoacetate-malate treatment decreased taurine levels to 75% of control and the activities of cysteine oxidase and cysteine sulfinate decarboxylase to 73 and 60% of control, respectively. Iodoacetate-malate treatment decreased taurine accumulation in vivo to only 12% of control; taurine uptake in vitro was also reduced to approximately 50% of control.

Subcellular distribution of cysteine oxidase activity in ox retina

Cysteine oxidase activity has been determined in the primary and secondary subfractions of ox retina. About 30% of enzyme activity is found in the soluble fraction while about 70% is associated with particulate components. In the secondary subcellular fractions about 36% of enzyme activity, recovered from crude mitochondria, is present in the synaptosomal fraction. Enzymic activity is stimulated by Fe ++ and NAD +. The reason and significance of the cysteine oxidase activity in synaptosomal fraction are briefly discussed in relation with taurine function in retina.

Cysteine oxidase in brain

Cysteine oxidase, which catalyzes the oxidation of cysteine to the neuroexcitatory and neurotoxic compounds cysteine sulfinic and sulfonic acids, previously has not been studied successfully in brain. Here we report optimal conditions for measuring cysteine oxidase activity in rat brain, describe its regional and subcellular distribution and compare activity during several stages of development. Employing NAD+ as cofactor, substantial activity was measurable in whole brain homogenate, 70% of which was localized to the microsomal fraction. Appreciable activity was present throughout brain with a 3-fold difference being detected between pons-medulla and cerebral cortex, the regions with the highest and lowest levels respectively. Cysteine oxidase activity in adult rat brain was approximately 5 times higher than that measured at birth. For the first 6 days of life there was very little change in activity; thereafter, a steady increase occurred with adult levels being reached between the 25th and 50th days.

Cysteine oxidase activity in rat retina during development

Cysteine oxidase activity has been determined in developing rat retina. Enzymic activity is present in 55, 000 × g supernate and in the crude mitochondria. Activity is rather low at birth; but increases with age; in mitochondria it reaches its maximum value at the 25th day while in supernate it increases more rapidly, reaching its maximum value 20 days after birth; unlike in the mitochondria, the activity of supernate considerably decreases during further development. The reason and significance of the postnatal changes in the mitochondrial cysteine oxidase activity are briefly discussed in relation with taurine formation.

Induction and activation of cysteine oxidase of rat liver II. The measurement of cysteine metabolism in vivo and the activation of in vivo activity of cysteine oxidase

1. 1. The incorporation of 14C into expired CO 2 from DL-[3- 14C]cysteine injected intraperitoneally into rats was slightly decreased by a loading dose of D-cysteine, whereas either the incorporation from DL-[1- 14C]cysteine or L-[U- 14C]-cysteine was unaffected by this loading. 2. 2. The incorporation of 14C into CO 2 from DL[1- 14C]cysteine or L-[U- 14C]-cysteine was remarkably elavated by L-cysteine loading. 3. 3. Hepatic cysteine oxidase activity was markedly induced by L-cysteine injection but cysteine desulfhydrase activity was not affected. 4. 4. The expected maximum 14CO 2 expirations expressed as C max and the C max half-times for DL-[1- 14C]cysteine, DL-[3- 14C]cysteine and L-[U- 14C]cysteine injected were calculated from the kinetics of 14CO 2 expiration as a function of time. 5. 5. The metabolic distributions of L-cysteine catabolism was calculated from these C max values; L-cysteine is metabolized 31% via the pyruvate pathway and 69% via the taurine pathway. 6. 6. Urinary excretion of 35S from L-[ 35S]cysteine injected was also examined. 7. 7. The facts presented in this paper strongly suggest that the degradation of L-cysteine is metabolized mainly through cysteine sulfinate, and therefore the incorporation of 14CO 2 into expired CO 2 from L-[U- 14C]cysteine is a reflection of the in vivo activity of cysteine oxidase and that the in vivo activity of cysteine oxidase was markedly enhanced by L-cysteine loading but not by D-cysteine loading.

Induction and activation of cysteine oxidase of rat liver: I. The effects of cysteine, hydrocortisone and nicotinamide injection on hepatic cysteine oxidase and tyrosine transaminase activities of intact and adrenalectomized rats

1. 1. The greatest increase in hepatic cysteine oxidase activity was observed in intact rats which received cysteine, but the increase in tyrosine transaminase activity mediated by cysteine was only one-half of that produced with nicotinamide or hydrocortisone. 2. 2. The decline of the elevated enzymic activity of either cysteine oxidase or tyrosine transaminase was delayed when these enzymes were induced by nicotinamide in intact rats. 3. 3. An additive increase in cystein oxidase activity in the intact rat was obtained by the simultaneous injection of nicotinamide with cysteine and of nicotinamide with hydrocortisone but not of cysteine with hydrocortisone. 4. 4. Hepatic cysteine oxidase and tyrosine transaminase activities in adrenalectomized rats were significantly increased after injection of hydrocortisone but not by cystein. Nicotinamide did produce a marked increase in tyrosine transaminase activity in adrenalectomized rats, while cysteine oxidase activity did not increase with either nicotinamide or cysteine. The hydrocortisone-mediated induction of hepatic cysteine oxidase activity was markedly enhanced by simultaneous injection of cysteine, but in the case of hepatic tyrosine transaminase activity, the hydrocortisone-mediated induction was not affected by cysteine injection. 5. 5. Cysteine-mediated induction of hepatic cysteine oxidase was partially inhibited by the simultaneous injection of cycloheximide, whereas hydrocortisone- and nicotinamide-mediated inductions were completely inhibited by cycloheximide.

Intermediary metabolism of cysteinesulfinic acid in cell-free extracts of Proteus vulgaris

1.1. The greatest increase in hepatic cysteine oxidase activity was observed in intact rats which received cysteine, but the increase in tyrosine transaminase activity mediated by cysteine was only one-half of that produced with nicotinamide or hydrocortisone.2.2. The decline of the elevated enzymic activity of either cysteine oxidase or tyrosine transaminase was delayed when these enzymes were induced by nicotinamide in intact rats.3.3. An additive increase in cystein oxidase activity in the intact rat was obtained by the simultaneous injection of nicotinamide with cysteine and of nicotinamide with hydrocortisone but not of cysteine with hydrocortisone.4.4. Hepatic cysteine oxidase and tyrosine transaminase activities in adrenalectomized rats were significantly increased after injection of hydrocortisone but not by cystein. Nicotinamide did produce a marked increase in tyrosine transaminase activity in adrenalectomized rats, while cysteine oxidase activity did not increase with either nicotinamide or cysteine. The hydrocortisone-mediated induction of hepatic cysteine oxidase activity was markedly enhanced by simultaneous injection of cysteine, but in the case of hepatic tyrosine transaminase activity, the hydrocortisone-mediated induction was not affected by cysteine injection.5.5. Cysteine-mediated induction of hepatic cysteine oxidase was partially inhibited by the simultaneous injection of cycloheximide, whereas hydrocortisone- and nicotinamide-mediated inductions were completely inhibited by cycloheximide.