Malic dehydrogenase assay

When linked enzyme assays are used, the exogenous added enzymes may also be contaminated with small traces of the primary enzyme whose activity is measured, thereby leading to falsely high activities In this instance it is also desirable to make certain that the added enzymes are free of any undesirable activity, i.e, pig heart malic dehydrogenase should be free of GOT activity when used for GOT assays (17),... 

Following are a set of assay conditions for marker enzymes of mitochondria (citrate synthetase, malic dehydrogenase, fumarase, and succinate dehydrogenase) and glyoxysomes (citrate synthetase, malate synthetase, and malic dehydrogenase). Some or all of these activities may be assayed across the density gradient. Their quantitative distribution is shown in Table 9-2. 

Both are abundant in skeletal muscle, myocardium, liver, and erythrocytes, so that hemolysis must be avoided, and in serum they may be assayed spectrophotometrically by their conversion of phosphate-buffered pyruvate to lactate (R6, W16) or oxalacetate to malate (S25) at the expense of added NADH2, when the rate of decrease of optical density at 340 m x thus measmes the serum activities of the respective enzymes. Recently, however, the reverse reaction has been found best for serum lactic dehydrogenase assay (A2a). In conventional spectrophotometric units the normal ranges are 100-600 units per ml for lactic dehydrogenase (W16) and 42-195 xmits per ml for malic dehydrogenase (S25) as before, one conventional spectrophotometric unit per ml = 0.48 pmoles/ minute/liter (W13). 

Glutamic-oxalacetate transaminase (GOT) is released into the blood stream as a result of myocardial infarction. The enzyme is assayed in serum by following the decrease in the absorbance of NADH in the malic dehydrogenase (MDH)-coupled reaction sequence shown below. 

The reaction mixture for a coupled assay includes the substrates for the initial or test enzyme and also the additional enzymes and reagents necessary to convert the product of the first reaction into a detectable product of the final reaction. The enzyme aspartate aminotransferase (EC 2.6.1.1), for instance, results in the formation of oxaloacetate, which can be converted to malic acid by the enzyme malate dehydrogenase (EC 1.1.1.37) with the simultaneous conversion of NADH to NAD+, a reaction which can be followed spectropho-tometrically at 340 nm ... 

It is not surprising that the pyruvic acid intermediate seemed plausible because in a paper earlier in that same year (23), the authors described a malic enzyme from pigeon liver. This enzyme was shown to form appreciable amounts of pyruvic acid from malic acid, but it was NADP instead of NAD specific. The end product was shown to be pyruvic acid by spectrophotometric assay involving lactate dehydrogenase. 

The main advantage of the proposed wine analysis is its selectivity because only primary amines can be detected using this method. Also, byproducts do not interfere with phenols or thiols. The quality of the wine and its organoleptic characteristics are well defined considering the effects of the malolactic fermentation process. The electrometric methods assure reliable results for the 1-malic and 1-lactic acids assay. The biosensors construction for 1-malic and 1-lactic acids assay in wine are based on malate dehydrogenase and lactate oxidase enzymes.117 The reproducibility of the results as well as the selectivity make it reliable for establishing the quality of the wine. 

The in vitro effect of 13-MTD on the enzymes involved in fatty acid biosynthesis was studied. Five enzyme activities were assayed FAS, acetyl-CoA carboxylase, glucose-6-phosphate dehydrogenase (G6PDH), adenosine triphosphate (ATP)-citrate lyase, and malic enzyme. Of the enzymes involved in fatty acid biosynthesis, FAS, acetyl-CoA carboxylase, and G6PD from rat liver were inhibited in vitro by 13-MTD [7],... 

The measurement of oxygen uptake provides a direct index of metabolic rate this measurement can be done simply by placing experimental animals In a calibrated vessel maintained at constant temperature and connected to an oxygen analyzer (86). Repeatedly used as an Index of thyromimetic activity have been the in vitro assay of oxygen uptake by suspended mitochondria and the spectrophotometric assays of rat liver mitochondrial a-glycerophosphate dehydrogenase (87) and of cytoplasmic malic enzyme (88). 

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