Hydrogen bonding lactate dehydrogenase

Fig. 22. An example of a long two-stranded ribbon of antiparallel jS structure, from lactate dehydrogenase (residues 263-294). Side chains are not shown hydrogen bonds are dotted. As is typical of isolated two-stranded ribbons, the chains show a very strong twist (180° in about five residues).

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. 

One of the first measures of how strongly hydrogen bonds can be reflected in isotope effects was the experimental determination of the oxygen isotope effect on binding of an inhibitor, oxamate, to lactate dehydrogenase.7 The inverse isotope effect... 

Several physical properties are influenced by the formation of hydrogen bonds UV and IR spectra, fluorescence behavior, and NMR spectra can be used to detect the presence of hydrogen bonds. Hydrogen bonds are identified in proteins whose three-dimensional structure is known at atomic resolution. As an example Fig. 3.9 shows hydrogen bonding in a protomer of lactate dehydrogenase (Rossmann et ai, 1972 Holbrook et aL, 1975), in both holo-enzyme and apoenzyme. 

Fig. 3.9, Hydrogen bonding of lactate dehydrogenase (according to Holbrook et aL, 1975). Hydrogen bonds are indicated for apoenzyme and for the ternary complex LDH-NAD" -pyruvate. Dotted bonds occur only in the ternary complex. (Courtesy of Rossmann.)... 

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