Lactate dehydrogenase subunits

L-Lactate dehydrogenase is a tetrameric enzyme whose four subunits occur in two isoforms, designated H (for... 

K15. Kanno, T., Sudo, K., Takeuchi, I., Kanda, S., Honda, N Nishimura, Y., and Oyama, K., Hereditary deficiency of lactate dehydrogenase M-subunit. Clin. Chim. Acta 108,267-276 (1980). 

K16. Kanno, T., and Maekawa, M Lactate dehydrogenase M-subunit deficiencies Clinical features, metabolic background, and genetic heterogeneities. Muscle Nerve (Suppl. 3), S54-S60 (1995). 

K21. Kitamura, M., Iijima, N Hashimoto, F., and Hiratsuka, A., Hereditary deficiency of subunit H of lactate dehydrogenase. Clin. Chim. Acta 34,419-423 (1971). 

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. 

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 ... 

The remaining three antiparallel /3 structures form a miscellaneous category (see Fig. 84). Lactate dehydrogenase d2 and gene 5 protein each has several two-stranded antiparallel j8 ribbons, but they do not coalesce into any readily described overall pattern. The N-terminal domain of tomato bushy stunt virus protein has a unique /3 structure in which equivalent pieces of chain from three different subunits wrap around a 3-fold axis to form what has been called a /3 annulus (Harrison et ah, 1978). Each of the three chains contributes a short strand segment to each of three three-stranded, interlocking /3 sheets. This domain provides one of the subunit contacts that hold the virus... 

The active form of lactate dehydrogenase (mass 144 kDa) is a tetramer consisting of four subunits (1). Each monomer is formed by a peptide chain of 334 amino acids (36 kDa). In the tetramer, the subunits occupy equivalent positions (1) each monomer has an active center. Depending on metabolic conditions, LDH catalyzes NADH-de-pendent reduction of pyruvate to lactate, or NAD -dependent oxidation of lactate to pyruvate (see p. 18). 

The active center of an LDH subunit is shown schematically in Fig. 2. The peptide backbone is shown as a light blue tube. Also shown are the substrate lactate (red), the coenzyme NAD (yellow), and three amino acid side chains (Arg-109, Arg-171, and His-195 green), which are directly involved in the catalysis. A peptide loop (pink) formed by amino acid residues 98-111 is also shown. In the absence of substrate and coenzyme, this partial structure is open and allows access to the substrate binding site (not shown). In the enzyme lactate NAD"" complex shown, the peptide loop closes the active center. The catalytic cycle of lactate dehydrogenase is discussed on the next page. 

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... 

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. 

Fig. 4.2. Covalent incorporation of [3H]3-(3H-diazirino)pyridine adenine dinucleotide into lactate dehydrogenase as a function of time. Lactate dehydrogenase (I. I mM in subunits) in 100 mM Tris-HCl at pH 8.0 was mixed with 3H]3-(3-H-diazirino) pyridine adenine dinu-...

Fushinobu, S., Ohta, T., and Matsuzawa, H. (1998). Homotropic activation via the subunit interaction and allosteric symmetry revealed on analysis of hybrid enzymes of L-lactate dehydrogenase./. Biol. Chem., 273, 2971-2976. 

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. 

Lactate dehydrogenase occurs as a tetramer with two kinds of subunits designated H for heart and M for muscle. Five different LDHs are separable and identifiable by electrophoresis. The composition of these and their major tissue locations are as follows ... 

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],... 

Fig. 18. Chain trace (centre) of a subunit of dogfish muscle lactate dehydrogenase. Diagrammatic representations (corners) show constituent parts of the structure, and their relationship to the bound coenzyme. From the work of Rossmann and colleagues [79],...

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