Circular dichroic properties and conformation of thionicotinamide dinucleotides bound to horse-liver alcohol dehydrogenase.

The study explores the interaction between horse liver alcohol dehydrogenase and the oxidized and reduced forms of the 3-thionicotinamide-adenine dinucleotide coenzyme analogues. The research investigates the properties, conformation, and potential binding of these complexes by using methods such as ultraviolet absorption, fluorescence, and circular dichroism.

Investigation of Interaction

• The research revolves around understanding the relationship between horse liver alcohol dehydrogenase and the oxidized and reduced forms of 3-thionicotinamide-adenine dinucleotide coenzyme analogues. This is carried out using ultraviolet absorption, fluorescence, and circular dichroism analytical methods.

Properties of sNAD and sNADH

• It is discovered in the study that the fluorescence of sNADH is enhanced when bound to the enzyme. Conversely, the protein fluorescence is reduced by both sNADH (60-65%) and sNAD (65%).
• A discussion is included in the research regarding the origin of the larger quenching produced by sNAD compared to that of NAD.

Coenzyme Dissociation Constants

• Coenzyme dissociation constants are determined by examining the quenching of the protein fluorescence. The research also discusses some kinetic consequences arising due to these dissociation constants.

Dichroic Properties and Conformation

• The study investigates the dichroic properties of various enzyme complexes, discussing them in terms of conformational changes and environmental alterations during coenzyme binding.
• Specific attention is paid to the conformation of sNAD when bound to the enzyme in the presence of trifluorethanol and the conformation of sNADH bound to the enzyme in the presence of isobutyramide.

Discussion of Spectral Data

• Apart from the investigations, a part of the research is dedicated to discuss the circular dichroic spectrum of the apoenzyme in terms of the contribution from aromatic amino acid residues in the specifically resolved 240-310nm region and in terms of helix content in the 220-nm region.