Lactate dehydrogenase EC

This tetrameric enzyme (subunit 36000) has been the subject of several crystallographic studies (summarized in [55]), and information on the dogfish isozyme has been obtained at high resolution [78]. The subunit structure [79] is illustrated in Fig. 18. On the basis of crystallographic findings, a numbering system for the amino acid chain was introduced [80], and has been widely used [55,79,81]. What were already known as Ser-163, Arg-171 and His-195 would simply become Ser-161, Arg-169 and His-193 in the consecutively numbered complete sequence [82]. However, in other parts of the chain (notably around residue 33, residue 187, and the regions 135-147 and 236-252) there were more extensive differences. For simplicity, 

This dimeric enzyme (subunit 35000) catalyses a reaction similar to the lactate dehydrogenase reaction, and the subunit structures of the enzymes are strikingly similar [83-85] (Fig. 20). Crystallographic [85] and other [86] evidence suggests that the reaction mechanisms are similar. The 4-pro-R hydrogen of NADH is transferred to the Re side of the oxaloacetate to give L-malate [87], 

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Figure 5. Example of dehydrogenase reactions which can be coupled with the bienzymatic bacterial bioluminescent system. ADH = alcohol dehydrogenase (EC 1.1.1.1), SDH = sorbitol dehydrogenase (EC 1.1.1.14), LDH = lactate dehydrogenase (EC 1.1.1.27), MDH = malate dehydrogenase (EC 1.1.1.37).

Figure 8.2 The effect of pH on the enzyme lactate dehydrogenase (EC 1.1.1.27). The enzyme shows maximum activity at pH 7.4 (A). When stored in buffer solutions with differing pH values for 1 h before re-assaying at pH 7.4, it shows complete recovery of activity from pH values between 5 and 9 but permanent inactivation outside these limits (B).

Figure 8.10 The quaternary structure of proteins. The enzyme lactate dehydrogenase (EC 1.1.1.27) has a relative molecular mass of approximately 140 000 and occurs as a tetramer produced by the association of two different globular proteins (A and B), a characteristic that results in five different hybrid forms of the active enzyme. The A and B peptides are enzymically inactive and are often indicated by M (muscle) and H (heart). The A4 tetramer predominates in skeletal muscle while the B4 form predominates in heart muscle but all tissues show most types in varying amounts.

Reactions do not necessarily go to completion and regardless of the amount of enzyme used, the equilibrium position of the reaction will not change. It is important for quantitative measurements that the reaction goes as near to completion as possible and this may be achieved by a variety of methods. The equilibrium position may be altered by changing the pH away from the optimum for the enzyme. For example, the equilibrium position for the reaction in which pyruvate is converted to lactate by lactate dehydrogenase (EC 1.1.1.27) lies very much towards pyruvate at the normal pH of 7.6 but at pH 9.0 the equilibrium is altered towards lactate. 

L-Amino acid oxidase has been used to measure L-phenylalanine and involves the addition of a sodium arsenate-borate buffer, which promotes the conversion of the oxidation product, phenylpyruvic acid, to its enol form, which then forms a borate complex having an absorption maximum at 308 nm. Tyrosine and tryptophan react similarly but their enol-borate complexes have different absorption maxima at 330 and 350 nm respectively. Thus by taking absorbance readings at these wavelengths the specificity of the assay is improved. The assay for L-alanine may also be made almost completely specific by converting the L-pyruvate formed in the oxidation reaction to L-lactate by the addition of lactate dehydrogenase (EC 1.1.1.27) and monitoring the oxidation of NADH at 340 nm. 

Fig. 22. Schematic presentation of the enzymatic synthesis of UDP-GalNH2 (33) including cofactor regeneration systems. A nucleoside monophosphate kinase (EC 2.7.7.4), B sucrose synthase (EC 2.4.1.13), C gal-l-P uridyltransferase (EC 2.7.7.12), D phosphoglucomutase (EC 2.7.5.1), E glucose-6-P dehydrogenase (EC 1.1.1.49), F lactate dehydrogenase (EC 1.1.1.27), G pyruvate kinase (EC 2.7.1.40) [319]...

Lactate dehydrogenase (EC 1.1.1.27 L-lactate NAD" oxidoreductase LD) is a hydrogen transfer enzyme that catalyzes the oxidation of L-lactate to pyruvate with the mediation of NAD as a hydrogen acceptor. 

Under certain conditions, the ratio of lactate to pyruvate is an indicator of redox status. By rearranging the equation for the equilibrium constant for the reaction catalyzed by lactate dehydrogenase (EC 1.1.1.27), it can be seen that the ratio of lactate to pyruvate is proportional to the ratio of NADH to NADL... 

Cytochrome 62 is also called yeast lactate dehydrogenase (EC 1.1.2.3, lactate cytochrome c oxidoreductase) (204 205]. This cytochrome possesses both FMN and protoheme (206-211). Although the native enzyme also contains deoxyribonucleic acid, this moiety can be removed by deoxyribonuclease without affecting the enzymic activity of the enzyme (212) and is supposed to be a heterogeneous component (213). This enzyme completely differs in its heme content from animal lactate dehydrogenase and also from yeast n(—)-lactate dehydrogenase. 

Figure 11.8 Mechanism of redox reaction catalyzed by NAD dependent lactate dehydrogenase Lactate dehydrogenase (EC 1.1.1.27) is a tetrameric enzyme which catalyzes the reversible redox reaction between L-lactate and pyruvate via ordered kinetic sequence. The hydride ion is transferred to the proR side of the 4 position of NAD. His 195 acts as an acid-base catalyst removing the proton from lactate during oxidation. The active site loop (residues 98-110) carries Argl09 which helps stabilize the transition state during hydride transfer and contacts required for the substrate specificity.

Lactate dehydrogenase (EC 1.1.1.27) catalyzes the reaction lactate-I-NAD pyruvate+NADH, which in the reverse direction represents the last reaction of anaerobic glycolysis. The enzyme consists of four identical polypeptide chains (subunits), each of molecular mass about 35 kDa. For a summary of this work, see Ref. [1]. 

Enzymes with niacin coenzymes in human metabolism (examples of 200 enzymes ). L-Lactate dehydrogenase (EC 1.1.1.27) alcohol dehydrogenase (EC l.l.l.l) glyceraldehyde-phosphate dehydrogenase (EC 1.2.1.12) NADPH-cytochrome-P-450-reductase (EC 1.6.2.4). 

In 14-day bleomycin (1.5 mg in sterile sahne i.p. daily)-treated rats (205 6 g body weight) type 2 alveolar epithelial cells were swollen with enlarged lamellar inclusion bodies (Karam et al. 1998). Biochemical study of freshly isolated cells displayed a significant decrease of lactate dehydrogenase (EC 1.1.1.27) released by these cells when isolated from 14-day-treated rats as compared with 7-day. By contrast, bleomycin induced an increase in superoxide dismutase (EC 1.15.1.1) and glutathione peroxidase (EC 1.11.1.9) activities. Cell content of glutathione was decreased and y-glutamyl transpeptidase activity was markedly increased. 

Rat lung inflammation 24 h after intratracheal instillation of diesel exhaust particles (Standard Reference Material 2975) initially exposed to 0.1 ppm [ 0]03 for 48 h was more potent in increasing neutrophilia, lavage total protein, and lactate dehydrogenase (EC 1.1.1.1.27) activity compared to unexposed diesel exhaust particles (Madden et al. 2000). Exposure of diesel exhaust particles to 1 ppm O3 led to a decreased bioactivity of the particles. 

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