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Methotrexate inhibits tetrahydrofolic acid production and influences mitochondrial oxygen uptake and activity of several enzymes in the respiratory chain reactions, which utilize nicotinamide adenine dinucleotide-linked (NAD-linked) substrates. Hyperproliferation of keratinocytes in psoriasis requires oxidative phosphorylation, in which the reduced form of nicotinamide adenine dinucleotide (NADH) is an electron donor. One hypothesis links increased cellular metabolism to the increased NADH/NAD+ ratio; as expected, the topical application of NAD+ (oxidized form of nicotinamide-adenine dinucleotide) resulted in a clinical improvement of psoriatic lesions in one study. Nevertheless, another report revealed reduced fluorescence of NADH in psoriatic plaques. The biological activity of NADH is not limited only to serving as the electron donor. It was also found to regulate gene transcription.

An end-point ADP/NAD(+) acid/alkali assay procedure, directly applicable to library screening of any type of ATP-utilising/ADP producing enzyme activity, was implemented. Typically, ADP production is coupled to NAD(+) co-enzyme formation by the conventional addition of pyruvate kinase and lactate dehydrogenase. Transformation of enzymatically generated NAD(+) into a photometrically active alkali derivative product is then achieved through the successive application of acidic/alkali treatment steps. The assay was successfully miniaturized to search for malate kinase activity in a structurally-guided library of LysC aspartate kinase variants comprising 6,700 clones. The screening procedure enabled the isolation of nine positive variants showing novel kinase activity on (L)-malate, the best mutant, LysC V115A: E119S:E434V exhibited strong substrate selectivity for (L)-malate compared to (L)-aspartate with a (k(cat)/K-m)(malate)/(k(cat)/K-m)(aspartate) ratio of 86. Double mutants V115A:E119S, V115A:E119C and E119S:E434V were constructed to further probe the origins of stabilising substrate binding energy gains for (L)-malate due to mutation. The introduction of less sterically hindering side-chains in engineered enzymes carrying E119S and V115A mutations increases the effective volume available for substrate binding in the catalytic pocket. Improved binding of the (L)-malate substrate may be assisted by less hindered movement of the Phe184 aromatic side-chain. Additional favourable long-range electostatic effects on binding arising from the E434V surface mutation are conditionally dependent upon the presence of the V115A mutation close to Phe184 in the active-site.

NAD is a pyridine nucleotide that is involved in cell metabolism and signaling of plant growth and stress. Recently, we reported on the multifaceted nature of NAD-inducible immunity in Arabidopsis. We identified NAD as an integral regulator of multiple defense layers such as production of ROS, deposition of callose, stimulation of cell death and modulation of defense metabolism including the defense hormones SA, JA and ABA, and other defense-associated metabolites. Altogether, NAD-induced immune effects confer resistance to diverse pathogenic microbes. Our addendum to this work further demonstrates an impact of NAD on the cytosolic calcium pool, a well-known component of early plant defense response.

Irrespective of their pyridine nucleotide specificity, all glutamate dehydrogenases; share a common chemical mechanism that involves an enzyme bound 'iminoglutarate' intermediate. Three compounds, structurally related to this intermediate, were tested for the inhibition of purified NADP-glutamate dehydrogenases from two Aspergilli, as also the bovine liver NAD(P)-glutamate dehydrogenase. 2-Methyleneglutarate, closely resembling iminoglutarate, was a potent competitive inhibitor of the glutamate dehydrogenase reaction. This is the first report of a non-aromatic structure with a better glutamate dehydrogenase inhibitory potency than aryl carboxylic acids such as isophthalate. A suitably located 2-methylene group to mimic the iminium ion could be exploited to design inhibitors of other amino acid dehydrogenases. (c) 2007 on behalf of the Federation of European Biochemical Societies.

Background/Aims: The synthesis of pyridine nucleotides from nicotinamide requires adenosine triphosphate. In man when exogenous nicotinamide is poorly utilized in this synthesis, the excess follows a dissipative metabolic pathway and is excreted in urine as N-methylnicotinamide. In human cirrhosis N-methylnicotinamide serum levels are higher than normal, in basal condition and after nicotinamide oral load, The aim of this study was to verify N-methylnicotinamide production in relation to hepatic content of adenosine triphosphate during in vitro perfusion of rat liver, in normal conditions and after adenosine triphosphate depletion by metabolic stress. Methods: ''Stress'' was obtained by pre-washing with saline for 15 min before the perfusion with nutritive medium. Results: The adenosine triphosphate decrease in the stressed liver was 38% after pre-washing with saline and 80% at the end of nutritive perfusion, In control liver the corresponding decreases were 1% after pre-washing with nutritive medium and 65% at the end of perfusion with the same medium, The total nicotinamide adenine dinucleotide decreases were 44% and 56% in the stressed liver, and 19% and 52% in the control liver, The output levels of N-methylnicotinamide at 90 min of rat liver nutritive perfusion were 31.50+/-4.72 nmol/g for normal liver and 66.40+/-13.17 for stressed liver (p

Narrow band (311 nm) UVB phototherapy is established treatment for psoriasis. DNA is a target for UVB via formation of cyclobutane pyrimidine dimers, which trigger loss of dendritic cells and macrophages, and inhibit CD4+ and CD8+ T cells. UV causes the formation of thymine dimers, which activate nuclear enzyme poly(ADP-ribose) polymerase. The fact that poly(ADP-ribose) polymerase utilizes nicotinamide-adenine dinucleotide (NAD) explains NAD decreases after UV irradiation. NADH regulates transcriptional repressor carboxyl-terminal binding protein, whereas NAD(+) is a co-substrate in deacylation reactions, engaged in genomic silencing. Hyperproliferation of psoriatic keratinocytes requires NADH during oxidative phosphorylation. In one study the NADH fluorescence (reflecting NADH amount) was reduced in psoriatic lesions. NAD(+) used topically was as effective as 0.1% anthralin. Spectrophotometry enables real-time measurements of NADH fluorescence in vivo in the epidermis and points out a new direction for application of biophysics in medicine.