Of malate dehydrogenase

A free energy study of malate dehydrogenase [29] using semiempirical QM-MM methods has also been reported, and that shidy also attributes many of the benefits to simulation of enzyme reactions found in the BPTP shidy. 

FIGURE 20,20 (a) The structure of malate dehydrogenase, (b) The active site of malate dehydrogenase. Malate is shown in red NAD" is blue. 

NADPH can be produced in the pentose phosphate pathway as well as by malic enzyme (Figure 25.1). Reducing equivalents (electrons) derived from glycolysis in the form of NADH can be transformed into NADPH by the combined action of malate dehydrogenase and malic enzyme ... 

Malik, P., McKenna, M. C. and Tildon, J. T. Regulation of malate dehydrogenases from neonatal, adolescent and mature rat brain. Neurochem. Res. 18 247-257,1992. 

Anderson BM, Noble C Jr, Gregory EM. 1977. Kepone inhibition of malate dehydrogenases. J Agric Food Chem 25(3) 485-489. 

In an earlier spectrophotometric study of this enzyme, a red shift of the reduced nicotinamide absorbance had been noted in the difference spectrum of the binding of reduced coenzyme to the purified protein. Fisher et al.92> had pointed out that this is characteristic of most B-stereo-specific dehydrogenases, so Biellman et al. have made a successful prediction for Fisher. Fisher s suggestion that the supernatant and mitochondrial forms of malate dehydrogenase have different stereospecificities for NAD+ has not been substantiated, however 89>. 

Students will isolate intact mitochondria from beef heart and fractionate them to prepare submitochondrial particles. Each fraction will be characterized by protein estimation by the biuret method and measurement of malate dehydrogenase and monoamine oxidase activity. 

Completion of all parts will require 4-5 hours. If time is limited (3 hours), it is recommended that students complete parts A and B and then test only for the presence of malate dehydrogenase in the intact mitochondria (part D). 

Use the plot of AiAQ vs. time to calculate AH/min over the linear portion of the curve. Convert the rate in absorbance terms to activity units. One enzyme unit is the amount of malate dehydrogenase that catalyzes the reduction of 1 micromole of oxaloacetate to L-malate in 1 minute under the described assay conditions. The reduction of 1 micromole of oxaloacetate leads to the oxidation of 1 micromole of NADH therefore, Equation E10.4 may be used to calculate the specific activity of malate dehydrogenase. 

Description of malate dehydrogenase. http //www.worthington-biochem.eom/manual/P/PAO.html. 

Acetic acid measurement involves conversion of acetate to acetyl-CoA by acetyl-CoA synthetase with the consumption of ATP (Boehringer Mannheim, 1986). Acetyl-CoA reacts with oxaloacetate and water in the presence of citrate synthetase to form citrate and CoA. Oxaloacetate for this reaction is obtained from malate by the action of malate dehydrogenase with concomitant conversion of NADH from NAD+. NADH is spectrophotometrically measured and correlated to acetic acid concentration. 

Figure 6.4. The effects of different inorganic salts on activity of malate dehydrogenase from an extremely halophilic archaeon (unpublished data of L. Borowitkza and G. Somero).

One illustration of this type of uncertainty comes from studies of paralogs of malate dehydrogenase. The mitochondrial paralog of malate dehydrogenase (mMDH) has long been... 

Lin, J.J., T.H. Yang, B.D. Wahlstrand, P.A. Fields, and G.N. Somero (2001). Phylogenetic relationships and biochemical properties of the duplicated cytosolic and mitochondrial isoforms of malate dehydrogenase from a teleost fish, Sphyraena idiastes. J. Mol. Evol., in press. 

Answer Malate dehydrogenase catalyzes the conversion of malate to oxaloacetate in the citric acid cycle, which takes place in the mitochondrion, and also plays a key role in the transport of reducing equivalents across the inner mitochondrial membrane via the malate-aspartate shuttle (Fig. 19-29). This shuttle requires the presence of malate dehydrogenase in the cytosol and the mitochondrial matrix. 

Special Function of Lactate Dehydrogenase Special Fimction of Malate Dehydrogenase Ketone Bodies... 

Tesfaye M., Temple SJ., Allan DL., Vance CP., Samac DA. Overexpression of malate dehydrogenase in transgenic alfalfa enhances organic add synthesis and confers tolerance to aluminum. Plant Physiology 2001 127(4) 1836-1844. 

A single polypeptide chain can in theory exist in an infinite number of different conformations. However, one specific conformation generally appears to be the most stable for any given sequence of amino acids, and this conformation is assumed by the chain as it is synthesized within the cell. Thus, the primary structure of the polypeptide chain also determines its three-dimensional secondary and tertiary structures. It is conceivable that in some cases there may be several alternative conformations ("conforraers ) of a single chain that are of nearly equal stabilities and therefore these alternative forms may coexist. This possibility was first suggested to account for the heterogeneity noted in preparations of the cytoplasmic and mitochondrial isoenzymes of malate dehydrogenase and has also been proposed as an explanation of the multiple electrophoretic zones of erythrocyte acid phosphatase. However, no multiple enzyme forms have been shown unequivocally to be due to conformational isomerism. 

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