Lactate dehydrogenase , types

Lactate dehydrogenase deficiency is an autosomal recessive myopathy caused by a genetic defect of the muscle subunit, which is encoded by a gene on chromosome 11 (type XI, Fig. 42-1). Thus far, several Japanese families and two Caucasian patients with this disease have been described. The clinical picture is characterized by cramps and myoglobinuria after intense exercise. 

Using two types of specially synthesized rhodium-complexes (12a/12b), pyruvate is chemically hydrogenated to produce racemic lactate. Within the mixture, both a d- and L-specific lactate dehydrogenase (d-/l-LDH) are co-immobilized, which oxidize the lactate back to pyruvate while reducing NAD+ to NADH (Scheme 43.4). The reduced cofactor is then used by the producing enzyme (ADH from horse liver, HL-ADH), to reduce a ketone to an alcohol. Two examples have been examined. The first example is the reduction of cyclohexanone to cyclohexanol, which proceeded to 100% conversion after 8 days, resulting in total TONs (TTNs) of 1500 for the Rh-complexes 12 and 50 for NAD. The second example concerns the reduction of ( )-2-norbornanone to 72% endo-norbor-nanol (38% ee) and 28% exo-norbornanol (>99% ee), which was also completed in 8 days, and resulted in the same TTNs as for the first case. 

After intratracheal instillation of nickel chloride or nickel sulphate in rats, a modest inflammatory response with increased number of macrophages and polynuclear leucocytes was obtained, together with increased activities of lactate dehydrogenase and -glucuronidase in bronchoalveolar fluid [351]. More severe lesions were characterized by type II cell hyperplasia with epithelialization of alveoli, and in some animals, fibroplasia of the pulmonary interstitium. By inhalation in rats, the nickel salts produced chronic inflammation and degeneration of the bronchiolar epithelium [352, 353]. There was also atrophy of the olfactory epithelium and hyperplasia of the bronchial and mediastinal lymph nodes. Nickel sulphate also produced a low incidence of emphysema and fibrosis [353]. 

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.

The isoenzymes within a particular family will operate under slightly different circumstances or may respond differently to metabolite feedback regulation. In this case there is some degree of structural similarity between the different isoenzymes. The usual example used to illustrate this point is lactate dehydrogenase (LD), which has five isoenzymes, each composed of four sub-units. The subunits are of two types, H or M, so the five forms arise as follows ... 

Elevated activities of liver enzymes (lactate dehydrogenase, aspartate aminotransferase, alanine aminotransferase, glutamate dehydrogenase) were found in the serum of rats exposed continuously to 26 ppm phenol vapor for 15 days (Dalin and Kristoffersson 1974). Increased concentration of these enzymes in serum is often associated with liver injury but is not conclusive evidence for the type or severity of injury. Therefore, 26 ppm can be considered a less serious LOAEL in rats. Serum levels of... 

Hillman JD, Andrews SW and Dzuback AL (1987) Acetoin production by wild-type strains and a lactate dehydrogenase-deficient mutant of Streptococcus mutans. Infect Immun 55, 1399-1402. 

A sequential enzyme-catalyzed reaction mechanism in which two substrates react to form two products and in which there is a preferred order in the binding of substrates and release of products. Several enzymes have been reported to have this type of binding mechanism, including alcohol dehydrogenase , carbamate kinase , lactate dehydrogenase , and ribitol dehydrogenase. ... 

When animal tissues cannot be supplied with sufficient oxygen to support aerobic oxidation of the pyruvate and NADH produced in glycolysis, NAD+ is regenerated from NADH by the reduction of pyruvate to lactate. As mentioned earlier, some tissues and cell types (such as erythrocytes, which have no mitochondria and thus cannot oxidize pyruvate to C02) produce lactate from glucose even under aerobic conditions. The reduction of pyruvate is catalyzed by lactate dehydrogenase, which forms the l isomer of lactate at pH 7 ... 

One of the first enzymes found to have isozymes was lactate dehydrogenase (LDH) (p. 538), which, in vertebrate tissues, exists as at least five different isozymes separable by electrophoresis. All LDH isozymes contain four polypeptide chains (each of Mt 33,500), each type containing a different ratio of two lands of polypeptides. The M (for muscle) chain and the H (for heart) chain are encoded by two different genes. 

Lactate dehydrogenase exists in the cytoplasm of humans and most animals as five forms which are easily separable by electrophoresis and are evenly spaced on electropherograms.8 This enzyme is a tetra-mer made of two kinds of subunits. Isoenzyme 1, which has the highest electrophoretic mobility, consists of four identical type B subunits. The slowest moving tetramer (isoenzyme 5) consists of four type A subunits, while the other three forms, AB3, A2B2, and A3B, contain... 

Most NAD+- or NADP+- dependent dehydrogenases are dimers or trimers of 20- to 40-kDa subunits. Among them are some of the first enzymes for which complete structures were determined by X-ray diffraction methods. The structure of the 329-residue per subunit muscle (M4) isoenzyme of lactate dehydrogenases (see Chapter 11) from the dogfish was determined to 0.25 nm resolution by Rossmann and associates in 1971.2 1 More recently, structures have been determined for mammaliam muscle and heart type (H4) isoenzymes,5 for the testicular (C4) isoenzyme from the... 

Kwan et al. [27] l-Lactate Yoghurt milk, soda, sport drinks, and healthy supplement Salicylate hydroxylase (SHL), L-lactate dehydrogenase (LDH), and pyruvate oxidase (PyOD)/entrapped by a poly(carbamoyl) sulfonate (PCS) hydrogel on a Teflon membrane Clark-type oxygen electrode ... 

Two enzymes are commonly used for amperometric biosensors, namely lactate oxidase (LOD) and lactate dehydrogenase (LDH). It should be noted that, in this instance, LOD refers to the enzyme which catalyses the reaction shown in Fig. 23.4, in which the products are pyruvate and H202. This type of enzyme was formerly assigned the E.C. number 1.1.3.2, but this was confused with lactate monooxygenase (E.C. 1.13.12.4), which is also commonly referred to as type I lactate oxidase [55] or simply lactate oxidase [56] whose products are acetate, C02 and H202. The LOD which catalyses the reaction shown in Fig. 23.4 has also been referred to as type II lactate oxidase [55] following clarification of this point in a published letter [57], current publications refer to this enzyme as E.C. 1.1.3.x. 

Lactate dehydrogenase (LDH) from Bacillus stearothermophilus, in its I51K D52S double mutant, exhibited a 56-fold increased specificity to NADPH over the wild-type LDH in a reaction mixture containing 15% methanol. Furthermore, the NADPH turnover number of this mutant was increased almost fourfold compared with wild-type LDH (Holmberg, 1999). 

The structure of an enzyme can also vary within a person, since different genes may encode enzymes that catalyse the same reaction. These enzymes are known as isozymes. Isozymes are often specific for different types of tissue. For example, lactate dehydrogenase (LDH) is produced in two forms, the M-type (muscle) and the H-type (heart). The M-type is predominates in tissue subject to anaerobic conditions, such as skeletal muscle and liver tissue, whereas the H-type predominates in tissue under aerobic conditions, such as the heart. Isozymes may be used as a diagnostic aid. For example, the presence of H-type LDH in the blood indicates a heart attack, since heart attacks cause the death of heart muscle with the subsequent release of H-type LDH into the circulatory system. 

An example of an enzyme which has different isoenzyme forms is lactate dehydrogenase (LDH) which catalyzes the reversible conversion of pyruvate into lactate in the presence of the coenzyme NADH (see above). LDH is a tetramer of two different types of subunits, called H and M, which have small differences in amino acid sequence. The two subunits can combine randomly with each other, forming five isoenzymes that have the compositions H4, H3M, H2M2, HM3 and M4. The five isoenzymes can be resolved electrophoretically (see Topic B8). M subunits predominate in skeletal muscle and liver, whereas H subunits predominate in the heart. H4 and H3M isoenzymes are found predominantly in the heart and red blood cells H2M2 is found predominantly in the brain and kidney while HM3 and M4 are found predominantly in the liver and skeletal muscle. Thus, the isoenzyme pattern is characteristic of a particular tissue, a factor which is of immense diagnostic importance in medicine. Myocardial infarction, infectious hepatitis and muscle diseases involve cell death of the affected tissue, with release of the cell contents into the blood. As LDH is a soluble, cytosolic protein it is readily released in these conditions. Under normal circumstances there is little LDH in the blood. Therefore the pattern of LDH isoenzymes in the blood is indicative of the tissue that released the isoenzymes and so can be used to diagnose a condition, such as a myocardial infarction, and to monitor the progress of treatment. 

Simulate these mutants for dogfish M4 lactate dehydrogeanse (6LDH.pdb). After energy minimization, superimpose the wild-type and mutant enzymes and construct their animated kinemage files including views for the complete molecular structures and close-ups of the L-lactate dehydrogenase active site as identified by the ProSite. 

Fig. 5.4. Two types of energy metabolism in cestodes. (a) Type 1 homolactate fermentation, (b) Type 2 Malate dismutation. Reaction 3 involves a carboxylation step decarboxylation occurs at 6, 7 and 10. Reducing equivalents are generated at reactions 6 and 7 one reducing equivalent is used at reaction 9. Thus, when the mitochondrial compartment is in redox balance and malate is the sole substrate, twice as much propionate as acetate is produced. Key 1, pyruvate kinase 2, lactate dehydrogenase 3, phosphoenolpyruvate carboxykinase 4, malate dehydrogenase 5, mitochondrial membrane 6 malic enzyme 7, pyruvate dehydrogenase complex 8, fumarase 9, fumarate reductase 10, succinate decarboxylase complex. indicates reactions at which ATP is synthesised from ADP cyt, cytosol mit, mitochondrion. (After Bryant Flockhart, 1986.)...

The relative activity of the fragmentary enzyme to the wild-type enzyme was much higher than that of the clipped to the native DadB enzyme. This was explained by the assumption that the thermostable enzyme has more extensive hydrophobic interdomain interactions than the DadB enzyme with less thermostability.12 The importance of hydrophobic interdomain interactions for catalysis was pointed out by studies on lactate dehydrogenase.23,24 ... 

Gerstein, M. and C. Chothia (1991). Analysis of protein loop closure. Two types of hinges produce one motion in lactate dehydrogenase. J. Mol. Biol. 220 133-149. 

Lactate dehydrogenase (LDH) is an oxidoreductase that catalyzes the conversion of lactate to pyruvate. It consists of four subunits that may be of two different types M and H ( muscle and heart formerly known as A and B, respectively). Five different isoenzymes are therefore possible, depending on the subunit composition ... 

The term "quaternary structure" refers to the interaction of several polypeptide chains in a noncovalent manner to form multisubunit protein particles termed oligomers. Individual subunit polypeptide chains are also referred to as protomers. Oligomers usually have an even number of subunits (two or more). The noncovalent interactions may be of the hydrophobic, hydrogen bond, or the polar type. Examples are hemoglobin and lactate dehydrogenase (four protomers each) and many allosteric enzymes. 

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