[Tear malate dehydrogenase, lactate dehydrogenase, and their isoenzymes in normal Chinese subjects and patients of ocular surface disorders].
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Levels of malate dehydrogenase (MDH), lactate dehydrogenase (LDH) and their isoenzymes in tears of normal Chinese subjects and patients with ocular surface disorders were determined. The normal values of tear LDH and MDH were found to be 45.51 +/- 23.00-81.35 +/- 37.84 mumol.s-1/L and 11.00 +/- 5.33-19.50 +/- 9.17 mumol.s-1/L respectively, disregarding sex or eye distinction. The LDH/MDH ratio reflected sensitively the metabolism of corneal and conjunctival epithelium. The MDH isoenzymes comprised MDHs and MDHm, the former accounting for 80.0%-89.1%. The LDH isoenzymes comprised 5 varieties, of which the ratio H/M of subunit H to subunit M was 0.196 +/- 0.02. The changes in LDH isoenzymes were helpful to the differential diagnosis of external eye diseases, and the increase of MDHm reflected sensitively the degree of injury to the corneal epithelium.Keywords:
Malate dehydrogenase
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Levels of malate dehydrogenase (MDH), lactate dehydrogenase (LDH) and their isoenzymes in tears of normal Chinese subjects and patients with ocular surface disorders were determined. The normal values of tear LDH and MDH were found to be 45.51 +/- 23.00-81.35 +/- 37.84 mumol.s-1/L and 11.00 +/- 5.33-19.50 +/- 9.17 mumol.s-1/L respectively, disregarding sex or eye distinction. The LDH/MDH ratio reflected sensitively the metabolism of corneal and conjunctival epithelium. The MDH isoenzymes comprised MDHs and MDHm, the former accounting for 80.0%-89.1%. The LDH isoenzymes comprised 5 varieties, of which the ratio H/M of subunit H to subunit M was 0.196 +/- 0.02. The changes in LDH isoenzymes were helpful to the differential diagnosis of external eye diseases, and the increase of MDHm reflected sensitively the degree of injury to the corneal epithelium.
Malate dehydrogenase
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A correlation is shown to exist between malate dehydrogenase (MDH), lactate dehydrogenase (LDH) and glycerol-3-phosphate dehydrogenase (glycerol-3-PDH activity values, lactate/pyruvate and malate/oxaloacetate coefficients, MDH and LDH isozyme spectra and kinetic properties of LDH isozymes in soluble fractions of cytoplasm from intact rabbit m. soleus (red), m. gastrocnemius (mixed) and m. quadratus lumborum (white). In denervated soleus and gastrocnemius the cytoplasmic MDH/LDH, mitochondrial MDH/LDH, MDH mitochondrial/MDH cytoplasmic activity ratios, concentrations of substrates and isozyme spectra of MDH and LDH tend to equalize. The obtained results indicate the importance of isozyme composition and total activity ratios of the dehydrogenases for regulation of pyruvate and NADH metabolic pathways.
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The activity of enzymes of nitrogen and energy metabolisms from dogfish liver and a commercial preparation Catrex manufactured in the Scientific-Industrial Association "Adaptogen" (Tbilisi) was studied. The liver homogenate contains active glutamate dehydrogenase (GD), malate dehydrogenase (MD) and lactate dehydrogenase (LD) catalysing in vitro the reaction in both directions, as well as active glutamine synthetase, aspartate transaminase and alanine transaminase. These enzymes are also present in Catrex, but their activities are less. After 10-day storage of the liver homogenate and the Catrex preparation the enzymes slightly inactivated. Two isozymes of MD and four isozymes of LD were detected in the liver homogenate by polyacrylamide gel electrophoresis. In Catrex the two MD isozymes and only three LD isozymes were found.
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Malate dehydrogenase fractions of the chick embryo were demonstrated after starch gel electrophoresis of homogenates of liver, brain and spleen. A total of seven malate dehydrogenase fractions were observed to occur in the chick embryo in an organ specific pattern. Treatment of the homogenates with urea, sodium chloride-sodium phosphate, and p-chloromercuribenzoate prior to electrophoresis revealed that only three distinct malate dehydrogenase-active proteins were presence. Two of these proteins exhibited properties similar to those previously reported for the supernatant malate dehydrogenase and mitochondrial malate dehydrogenase of other species. Becuase of the differing properties of chick malate and lactate dehydrogenase it is concluded that the molecular basis for malate dehydrogenase isozymes is different from that reported for lactate dehydrogenase isozymes.
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A non-invasive biochemical technique for quantifying the effects of anterior corneal hypoxia on the in vivo corneal epithelium of the human eye is described. Following short-term exposure of the cornea to low atmospheric oxygen pressures, lactate dehydrogenase (LDH) and malate dehydrogenase (MDH) activities in tears are altered so that the tear LDH/MDH ratio is elevated. The degree of elevation of the ratio and its timing are related to the severity of hypoxia. Possible explanations for the elevation of the tear LDH/MDH ratio include unbinding of intracellular LDH and increased cell membrane permeability. For severe hypoxia, de novo LDH synthesis may also contribute. These changes suggest that control mechanisms within the corneal epithelium may be responding to optimize the efficiency of anaerobic metabolism during conditions of environmental stress, and offer the prospect of a non-invasive technique for monitoring epithelial metabolic stress.
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A non-invasive biochemical technique for quantifying the effects of anterior corneal hypoxia on the in vivo corneal epithelium of the human eye is described. Following short-term exposure of the cornea to low atmospheric oxygen pressures, lactate dehydrogenase (LDH) and malate dehydrogenase (MDH) activities in tears are altered so that the tear LDH/MDH ratio is elevated. The degree of elevation of the ratio and its timing are related to the severity of hypoxia. Possible explanations for the elevation of the tear LDH/MDH ratio include unbinding of intracellular LDH and increased cell membrane permeability. For severe hypoxia, de novo LDH synthesis may also contribute. These changes suggest that control mechanisms within the corneal epithelium may be responding to optimize the efficiency of anaerobic metabolism during conditions of environmental stress, and offer the prospect of a non-invasive technique for monitoring epithelial metabolic stress.
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