This review concentrates on advances in nitric oxide synthase (NOS) structure, function and inhibition made in the last seven years, during which time substantial advances have been made in our understanding of this enzyme family. There is now information on the enzyme structure at all levels from primary (amino acid sequence) to quaternary (dimerization, association with other proteins) structure. The crystal structures of the oxygenase domains of inducible NOS (iNOS) and vascular endothelial NOS (eNOS) allow us to interpret other information in the context of this important part of the enzyme, with its binding sites for iron protoporphyrin IX (haem), biopterin, L-arginine, and the many inhibitors which interact with them. The exact nature of the NOS reaction, its mechanism and its products continue to be sources of controversy. The role of the biopterin cofactor is now becoming clearer, with emerging data implicating one-electron redox cycling as well as the multiple allosteric effects on enzyme activity. Regulation of the NOSs has been described at all levels from gene transcription to covalent modification and allosteric regulation of the enzyme itself. A wide range of NOS inhibitors have been discussed, interacting with the enzyme in diverse ways in terms of site and mechanism of inhibition, time-dependence and selectivity for individual isoforms, although there are many pitfalls and misunderstandings of these aspects. Highly selective inhibitors of iNOS versus eNOS and neuronal NOS have been identified and some of these have potential in the treatment of a range of inflammatory and other conditions in which iNOS has been implicated.

This review concentrates on advances in nitric oxide synthase (NOS) structure, function and inhibition made in the last seven years, during which time substantial advances have been made in our understanding of this enzyme family. There is now information on the enzyme structure at all levels from primary (amino acid sequence) to quaternary (dimerization, association with other proteins) structure. The crystal structures of the oxygenase domains of inducible NOS (iNOS) and vascular endothelial NOS (eNOS) allow us to interpret other information in the context of this important part of the enzyme, with its binding sites for iron protoporphyrin IX (haem), biopterin, l-arginine, and the many inhibitors which interact with them. The exact nature of the NOS reaction, its mechanism and its products continue to be sources of controversy. The role of the biopterin cofactor is now becoming clearer, with emerging data implicating one-electron redox cycling as well as the multiple allosteric effects on enzyme activity. Regulation of the NOSs has been described at all levels from gene transcription to covalent modification and allosteric regulation of the enzyme itself. A wide range of NOS inhibitors have been discussed, interacting with the enzyme in diverse ways in terms of site and mechanism of inhibition, time-dependence and selectivity for individual isoforms, although there are many pitfalls and misunderstandings of these aspects. Highly selective inhibitors of iNOS versus eNOS and neuronal NOS have been identified and some of these have potential in the treatment of a range of inflammatory and other conditions in which iNOS has been implicated.

Objective: to evaluate the impact of Leiden mutation on the course of severe acute pancreatitis. Subjects and methods. One hundred and twelve people were examined. Group 1 comprised 50 patients diagnosed with severe acute pancreatitis with out coagulation factor V (Leiden) mutation. Group 2 included 42 patients with severe acute pancreatitis who were found to have Leiden mutation. Acute pancreatitis was first diagnosed in both groups. Group 3 consisted of 20 apparently healthy individuals (a control group). The severity of the underlying disease was determined in accordance with the clinical and lab oratory parameters recommended by the I. I. Dzhanelidze Saint Petersburg Research Institute of Emergence Care. Results. This investigation revealed an association of Leiden mutation with trends in the development of acute pancreatitis. Group 2 exhibited a more severe disease: large focal pancreatic necrosis was twice more common and infectious complica tions developed more frequently; more aggressive and rad ical treatments were more often used. The patients with Leiden mutation had higher mortality rates (33% in the Leiden mutation group and 24% in the non mutation group.

Nitric oxide (NO) reversibly inhibited oxygen consumption of brain synaptosomes. Inhibition was reversible, occurred at the level of cytochrome oxidase, and was apparently competitive with oxygen, with half-inhibition by 270 nM NO at oxygen concentrations around 145 PM and by 60 nM NO at around 30 PM Oz. Isolated cytochrome oxidase was inhibited by similar levels of NO. These levels of NO are within the measured physiological and pathological range for a number of tissues and conditions, suggesting that NO inhibition of cytochrome oxidase and the competion with oxygen may occur in vivo.

The four gases, nitric oxide (NO), carbon monoxide (CO), hydrogen sulfide (H(2)S) and hydrogen cyanide (HCN) all readily inhibit oxygen consumption by mitochondrial cytochrome oxidase. This inhibition is responsible for much of their toxicity when they are applied externally to the body. However, recently these gases have all been implicated, to greater or lesser extents, in normal cellular signalling events. In this review we analyse the chemistry of this inhibition, comparing and contrasting mechanism and discussing physiological consequences. The inhibition by NO and CO is dependent on oxygen concentration, but that of HCN and H(2)S is not. NO and H(2)S are readily metabolised by oxidative processes within cytochrome oxidase. In these cases the enzyme may act as a physiological detoxifier of these gases. CO oxidation is much slower and unlikely to be as physiologically important. The evidence for normal physiological levels of these gases interacting with cytochrome oxidase is equivocal, in part because there is little robust data about their steady state concentrations. A reasonable case can be made for NO, and perhaps CO and H(2)S, inhibiting cytochrome oxidase in vivo, but endogenous levels of HCN seem unlikely to be high enough.