The three-dimensional structures of dogfish M4 (muscle) and pig H4 (heart) lactate dehydrogenase (L-lactate:NAD+ oxidoreductase, EC 1.1.1.27) have been determined and correlated with the amino acid sequences of the dogfish M4, pig M4, pig H4, chicken M4, and chicken H4 lactate dehydrogenase isozymes. These results have been related to the known differences of physicochemical properties between the M and H lactate dehydrogenase isozymes. By far the largest structural alterations occur in the transition between the "apo" and "ternary complex" conformational states of the enzyme rather than between species or isozymes. The major catalytic difference can be explained by a replacement of alanine (in the M chain) with a glutamine (in the H chain) in the vicinity of the binding site of the coenzyme phosphates. The known immunological differentiation of the M and H isozymes is consistent with the differences in their amino acid sequences.The subunits of lactate dehydrogenase (LDH; L-lactate:NAD+ oxidoreductase, EC 1.1.1.27) exist as two major structural forms, usually referred to as M (muscle) and H (heart) or A and B, respectively, which give rise to five different isozymes of the tetrameric molecule (1, 2) in higher vertebrates. The differences in the properties of the LDH isozymes are dependent on their subunit composition and are most exaggerated between the homotetramers M4 (LDH-5) and H4 (LDH-1). The most important of these differences are (independent of species): (i) The turnover number of the M4 isozyme is generally about twice that for the H4 isozyme (3-5).(ii) The activity of the H4 isozyme is more readily diminished by modification of the carboxyamide group on the 3 position of the nicotinamide (6). For instance, acetylpyridine adenine dinucleotide reduces the rate of catalysis by at least five when compared to NAD in the H4 enzyme, whereas the M4 isozyme is not especially sensitive to this difference of the NAD molecule (7). (iMi) The forward reaction lactate-to-pyruvate is inhibited to a far greater extent by high concentrations of pyruvate in the H4 than in the M4 isozyme (5, 7-9). (iv) Both the enzymic activity and the affinity of the substrate for enzyme are reduced to a greater extent in the M4 isozyme as the length of the aliphatic chain of the a-keto acid increases (10-12). (v) The H4 isozyme binds oxidized or reduced coenzyme better than the M4 isozyme (13-20). (vi) An antiserum induced in rabbit against the M4 isozyme of one species will crossreact with the M4 isozyme from several closely related species but not with the H4 isozyme of the same species (4,(21)(22)(23)(24)(25). Some appreciation of these differences is now possible from a correlation of recent studies on three-dimensional and primary structures of the H4 and M4 LDH isozymes.The tertiary structure of dogfish M4 LDH has been determined independently for the apo-enzyme and for a complex of LDH, coenzyme, and substrate analogue. The apo-enzyme has been studied at 2.0-A resolution, while a series of isomorphous ternary complexes h...

The structures of the oligosaccharides of the hemagglutinin of fowl plague virus [influenza A/FPV/Rostock/34 (H7N1)] have been elucidated by one‐ and two‐dimensional 1H n.m.r. spectroscopy at 500 MHz and by microscale methylation analysis. N‐Glycosidic oligosaccharides of the oligomannosidic (OM) and of the N‐acetyllactosaminic type have been found, the latter type comprising biantennary structures, without (A) or with (E) bisecting N‐acetylglucosamine, and triantennary (C) structures. Analysis of the tryptic and thermolytic glycopeptides of the hemagglutinin allowed the allocation of these oligosaccharides to the individual glycosylation sites. Each attachment site contained a unique set of oligosaccharides. Asn12 contains predominantly structures C and E which are highly fucosylated. Asn28 contains OM and A structures that lack fucose and sulfate. Asn123 shows A that has incomplete antennae but is highly fucosylated and sulfated. Asn149 has fucosylated A and E. Asn231 shows fucosylated A and E with incomplete antennae. Asn406 has OM oligosaccharides. Asn478 has A and E with little fucose. Localization of the oligosaccharides on the three‐dimensional structure of the hemagglutinin revealed that the oligomannosidic glycans are attached to glycosylation sites at which the enzymes responsible for carbohydrate processing do not have proper access. These observations demonstrate that an important structural determinant for the oligosaccharide side chains is the structure of the glycoprotein itself. In addition, evidence was obtained that the rate of glycoprotein synthesis also has an influence on carbohydrate structure.

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Intrachain disulfide bonds between paired cysteines in the glycoprotein (G) of vesicular stomatitis virus (VSV) are required for the recognition of discontinuous epitopes by specific monoclonal antibodies (MAbs) (W.