Retinal oxidase

Retinoic acid is a metabolic product of vitamin A that supports the growth and differentiation of epithelial tissues. Retinoic acid is formed in the cytosol by the reversible oxidation of retinol to retinal, and the irreversible oxidation of retinal to retinoic acid. There is controversy as to whether retinal is oxidized by retinal dehydrogenase, which is linked to NAD+, or by retinal oxidase. 

Retinoic acid, retinol, and retinal are separated on a reversed-phase C 8 column (4.6 mm x 150 mm, 5 /urn). The mobile phase consisted of acetoni-trile-1% ammonium acetate (60 40) for 6.0 minutes, a linear gradient to 100% acetonitrile in 0.5 minute, then a hold at 100% acetonitrile for 3.0 minutes, followed by a linear gradient back to the initial conditions in 0.5 minute. The system was allowed to equilibrate for 4.0 minutes before the next injection was made. The flow rate was 2.0 mL/min throughout. The column effluent was monitored at 340 nm. 

Retinal oxidase was assayed in a medium containing 0.1 M phosphate buffer (pH 7.7) and 10 piL of 25 mM retinal dispersed in acetone containing 5% Triton X-100. The reaction was initiated by adding 20 to 40 fih of reconstituted ammonium sulfate precipitate or cytosol. The final volume was 500 /xL. The reaction was continued at 37°C for 30 minutes and was stopped by freezing at -70°C, whereupon 50 juL was injected directly onto the column. Enzyme activity was linear with protein concentration up to 2.4 mg/mL, and with time up to 30 minutes. 

The enzyme can be assayed in cytosol prepared by conventional means, or in the dissolved pellet obtained from treatment of cytosol with ammonium sulfate added to 45% of saturation. 

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In first central cleavage step, P-carotene (2) was converted to retinal (16) by P,P-carotene 15,15 -monooxygenase, and followed by retinol (18), retinyl esters of the storage forms such as retinyl acetate (22), retinol (18), retinal (16) by each enzyme, and finally retinoic acid (20) by retinal oxidase (Figure 5). 

Rieger JM, Shah AR, Gidday JM (2002) Ischemia-reperfusion injury of retinal endothelium by cyclooxygenase- and xanthine oxidase-derived superoxide. Exp. Eye Res. 74 493-501. 

Proton gradients can be built up in various ways. A very unusual type is represented by bacteriorhodopsin (1), a light-driven proton pump that various bacteria use to produce energy. As with rhodopsin in the eye, the light-sensitive component used here is covalently bound retinal (see p. 358). In photosynthesis (see p. 130), reduced plastoquinone (QH2) transports protons, as well as electrons, through the membrane (Q cycle, 2). The formation of the proton gradient by the respiratory chain is also coupled to redox processes (see p. 140). In complex III, a Q,cycle is responsible for proton translocation (not shown). In cytochrome c oxidase (complex IV, 3), trans-... 

Upton AL, Salichon N, Lebrand C, Ravary A, Blakely R, Seif 1, Gaspar P (1999) Excess of serotonin (5-HT) alters the segregation of ipsilateral and contralateral retinal projections in monoamine oxidase A knock-out mice possible role of 5-HT uptake in retinal ganglion cells during development. J Neurosci 19 7007-7024... 

The enzymes are widely distributed in microorganisms, plants, and animals. " Three Mo-MPT enzymes have been found in mammals (1) xanthine dehydrogenase see Dehydrogenase) has many, varied roles in purine catabolism, drug metabolism, and oxidative stress response, (2) aldehyde oxidase is important in drug metabolism and the synthesis of retinoic acid from retinal, and (3) sulfite oxidase plays a cmcial role in the detoxification of sulfite produced in the degradation of cysteine and methionine. Genetic Mo-MPT deficiency in... 

Wu, G.S. and N.A. Rao Activation of NADPH oxidase by docosahexaenoic acid hydroperoxide and its inhibition by a novel retinal pigment epithehal protein. Invest Ophthalmol. Vis. Sci. 40 (1999) 831-9. 

The following types of bion ihbrane stacks were investigated by paraciystal-line methods nerve myelin retinal rod outer segment discs human erythrocyte ost membranes sarcoplasmic reticulum chromatophore membrane cytochrome oxidase model membranes photosynthetic membranes. " mitochondrial cristae membranes ... 

The mechanism of ethambutol-induced optic neuropathy is unclear. It has been postulated that it is caused by a disturbance in mitochondrial metabolism. Ethambutol is also a strong chelator of copper, a co-factor of cytochrome c oxidase, which is required for axonal transport in the optic nerves, failure of which, secondary to mitochondrial insufficiency, results in optic neuropathy. Ethambutol is specifically toxic to retinal... 

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