8-Bromo-adenosine diphosphoribose (br'ADP-Rib) and nicotinamide 8-bromoadenine dinucleotide (Nbr'AD') which are analogues of the coenzyme NAD' , were prepared and their liver alcohol dehydrogenase complexes studied by crystallographic methods. Nbr'AD' is active in hydrogen transport and br' ADP-Rib is a coenzyme competitive inhibitor for the enzymes liver alcohol dehydrogenase and yeast alcohol dehydrogenase. X-ray data were obtained for the complex between liver alcohol dehydrogenase and br8ADP-Rib to 0.45 nm resolution and for the liver alcohol dehydrogenase-adenosine diphosphoribose complex to 0.29-nm resolution. The conformations of these analogues were determined from the X-ray data. It was found that ADP-Rib had a conformation very similar to the corresponding part of NAD', when NAD' is bound to lactate and malate dehydrogenase.br'ADP-Rib had the same anti conformation of the adenine ring with respect to the ribose as ADP-Rib and NAD', in contrast to the syn conformation Sound in 8-bromo-adenosine. The overcrowding at the 8-position is relieved in br'ADP-Rib by having the ribose in the 2' endu conformation instead of the usual 3' endo as in ADP-Rib and NAD'.

The fluorescence properties of horse-liver alcohol dehydrogenase were investigated with the aim of separating the contribution of Trp-15 (which is close to the protein surface) from that of Trp-314 (buried in the interior of the protein). Quenching of the protein fluorescence by iodide involves, to a larger degree, the longer wavelength region of the protein emission spectrum and is interpreted to involve only , , at 340 nm and a quantum yield of 0.19). It is shown that quenching by NAD and NADH involves both types of tryptophan, but the 'blue' one to a larger extent. In the case of NADH, radiationless energy transfer between enzyme and reduced nicotinamide ring accounts for less than one half of the total protein fluorescence quenching. Energy transfer between the tryptophan and adenine rings is also possible, but it cannot account for the rest of the protein quenching. Thus, it is suggested that protein conformational changes, following NADH binding, are the cause of part of the fluorescence quenching. The extent to which quenching by NAD can be ascribed to radiationless energy transfer processes is also calculated. It is shown that despite the small spectral overlapping between coenzyme absorption and protein emission, the energy transfer contribution cannot be neglected. However, it is very likely that also in this case a sizeable part of the protein fluorescence quenching comes from protein conformational changes following coenzyme binding. The possible nature of these conformational changes is discussed, taking into account recent X-ray data of enzyme-coenzyme complexes.Horse-liver alcohol dehydrogenase has four tryptophan residues, two per subunit of molecular weight 40000 [l]. Recent X-ray data locate them spatially: Trp-15 is close to the surface and probably exposed to water, while Trp-314 is buried inside the protein, close to the interaction domain of the two subunits property has been used in a number of ways in order to study the interaction between the apoenzyme and coenzyme [4-81. The quenching produced by binding of NADH is usually attributed to energy transfer [5,8] whereas the quenching upon binding of NAD, analogous to the cases of octopine dehydrogenase [9] and yeast alcohol dehydrogenase [I 01, has been ascribed to a protein conformational change [7]. The present work analyzes the overall protein fluorescence in terms of the contribution of the two types of tryptophan residues. It will be shown that it

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The concept of a coupled quantales is introduced as a non-commutative extension of the concept of biframes. Also an approach to non-commutative bitopology is studied. Then an adjunction between the category of coupled quantales and the category of biquantum spaces is established.