다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

For a long time, superoxide generation by an NADPH oxidase was considered as an oddity only found in professional phagocytes. Over the last years, six homologs of the cytochrome subunit of the phag...

/pdf/the-nox-family-of-ros-generating-nadph-oxidases-physiology-zjc88zvh59.pdf

The NOX Family of ROS-Generating NADPH Oxidases: Physiology and Pathophysiology

Flavonoids are nearly ubiquitous in plants and are recognized as the pigments responsible for the colors of leaves, especially in autumn. They are rich in seeds, citrus fruits, olive oil, tea, and red wine. They are low molecular weight compounds composed of a three-ring structure with various substitutions. This basic structure is shared by tocopherols (vitamin E). Flavonoids can be subdivided according to the presence of an oxy group at position 4, a double bond between carbon atoms 2 and 3, or a hydroxyl group in position 3 of the C (middle) ring. These characteristics appear to also be required for best activity, especially antioxidant and antiproliferative, in the systems studied. The particular hydroxylation pattern of the B ring of the flavonoles increases their activities, especially in inhibition of mast cell secretion. Certain plants and spices containing flavonoids have been used for thousands of years in traditional Eastern medicine. In spite of the voluminous literature available, however, Western medicine has not yet used flavonoids therapeutically, even though their safety record is exceptional. Suggestions are made where such possibilities may be worth pursuing.

The Effects of Plant Flavonoids on Mammalian Cells:Implications for Inflammation, Heart Disease, and Cancer

Curcumin, a polyphenolic compound derived from dietary spice turmeric, possesses diverse pharmacologic effects including anti-inflammatory, antioxidant, antiproliferative and antiangiogenic activities. Phase I clinical trials have shown that curcumin is safe even at high doses (12 g/day) in humans but exhibit poor bioavailability. Major reasons contributing to the low plasma and tissue levels of curcumin appear to be due to poor absorption, rapid metabolism, and rapid systemic elimination. To improve the bioavailability of curcumin, numerous approaches have been undertaken. These approaches involve, first, the use of adjuvant like piperine that interferes with glucuronidation; second, the use of liposomal curcumin; third, curcumin nanoparticles; fourth, the use of curcumin phospholipid complex; and fifth, the use of structural analogues of curcumin (e.g., EF-24). The latter has been reported to have a rapid absorption with a peak plasma half-life. Despite the lower bioavailability, therapeutic efficacy of...

Bioavailability of curcumin: problems and promises.

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.

/pdf/nitric-oxide-synthases-structure-function-and-inhibition-1t31plqilr.pdf

Nitric oxide synthases: structure, function and inhibition

ing species placed symmetrically between the endo and exo hydrogens could result in a G value of I, with subsequent asymmetric placement of the oxygen atom selectively at the exo face. The specificity of oxygen atom transfer from the exo face of the camphor skeleton is further demonstrated by the epoxidation of 5 ,6-dehydrocamphor.211 High-resolution NMR and 180rlabeling studies indicate that the product is completely the exo isomer and one atom from molecular oxygen is inserted to form the epoxide. This further emphasizes the apparent geometry of the activated oxygen species as being more closely situated at the exo face of camphor. As for hydroxylation of the natural substrate, the stereochemistry of the epoxidation reaction is the same for the NADH-, iodosobenzene-, and HzOz-driven turnovers. Epoxidations in model systems have been well documented. 234 As with the hydroxylation reactions, differences in the stereochemistry of epoxidation by Mn(III)TPP versus Fe(IIl)TPP may reflect differences in the lifetime of the radical species generated. The absolute stereoselectivity of oxygen insertion at the exo face of camphor is very reminiscent of the rigorous stereochemical integrity of product formation observed with the P-450scc enzyme. Here, cholesterol is hydroxylated at the 22and 20-position to afford (20R, 22R)-dihydroxyBACfERIAL P-450 ENZYMES 477 cholesterol as an intermediate in the production of pregnenolone.235-237 No other stereoisomeric products are obtained with those steroid-metabolizing activities. Nevertheless, the stereochemical parallel to P-450cam cannot be extended to the hydrogen abstraction step since evidence for such a chemical step is tenuous at best in these systems. When 22R-[223H]cholesterol was incubated with a side-chain cleavage preparation, the 22R-[22-3H]-22-hydroxycholesterol intermediate had negligible loss of radioactivity. This suggests selectivity in the hydrogen abstraction if it occurs. On the other hand, the loss of even a small amount of tritium may in fact suggest possible abstraction of either enantiotopic hydrogen in the natural cholesterol, especially when one consdiers the large isotopic selectivity expected for hydrogen rather than tritium. So, whereas, the insertion of the oxygens into the cholesterol side chain demonstrates strict stereochemical selectivity, a systematic investigation of the stereochemistry of the putative hydrogen abstraction steps has not been performed. As mentioned previously, when norbornane is hydroxylated by P-450LM20 both the 2-exoand 2-endo-alcohols are produced. 193 Also, the four exo-hydrogens were replaced by deuterium, and the deuterium-containing product alcohols were examined. It was found that the exo-2norborneol contained four deuteriums, whereas the endo-2-norborneol contained three deuteriums. This demonstrates an interesting contrast to the P-450cam stereochemistry, assuming both P-450LM2 and P-450cam proceed via a similar hydrogen-abstracted substrate species. These norborneol products demonstrate endo abstraction followed by exo rebound, and exo abstraction followed by endo rebound. Thus, both P-450LM2 and P-450cam are capable of endo or exo hydrogen abstraction, although P450cam displays absolute stereochemical control in the oxygen transfer step. This lack of complete stereochemical integrity of oxygen insertion is perhaps explained by a great degree of substrate motion at the active site of P-450LM2 as compared to P-450cam. A comparison of substrate regioselection has been made directly between these two isozymes using camphor, adamantanone, and adamantane as substrates. 154 As expected, P-450LM2 gave both 5-exoand 5-endo-hydroxycamphor, a result analogous to what was observed with norbornane. Also evident were 3-exoand 3-endo-hydroxycamphor. The greater stereoselectivity of oxygen insertion by P-450cam was observed with the other substrates as well (Table V). With P-450cam as the catalyst, 5-hydroxyadamantanone and 1-adamantanol were produced from the nonhydroxylated substrates. As the 5and 1-carbons of these substrates are tertiary, only one isomeric alcohol is possible for these products. With P-450LM2 , adamantanone was processed to 4-antiand 5-hydroxyadamantanone, while adamantane was hydroxylated at both the 1and 2-positions. The authors predict which

Cytochrome P-450

In chemical terms, the regio- and stereoselective hydroxylation of hydrocarbon C-H bonds is a very difficult transformation. Nevertheless, these reactions are deftly catalyzed by a variety of metalloenzymes, among which the most diverse are the many members of the cytochrome P450 family. Cytochrome P450 enzymes are found in most classes of organisms, including bacteria, fungi, plants, insects, and mammals. Thousands of such proteins are now known (http://drnelson.utmem.edu/cytochromeP450.html), including 57 in the human genome (1), 20 in Mycobacterium tuberculosis (2), 272 in Arabidopsis (3), and the amazing number of 457 in rice (4). The nomenclature for these enzymes is based on their sequence similarity when appropriately aligned, a somewhat arbitrary similarity cutoff (approximately >40% identity) being used to define members of a family and a higher cutoff (approximately >55% identity) members of a subfamily (5). Thus CYP3A4 corresponds to the fourth enzyme in family 3, subfamily A. This nomenclature allows the naming of enzymes without regard to their origin or specific properties.

The mammalian, plant, and fungal proteins are commonly membrane bound and are relatively difficult to manipulate, but the bacterial proteins are usually soluble, monomeric proteins. For that reason, much of the early research on mechanisms of cytochrome P450 enzymes was carried out with bacterial enzymes, particularly with the prototypical enzyme CYP101 (P450cam) from Pseudomonas putida (6, 7). From a chemist's point of view, there is a particular interest in the thermophilic enzymes, which currently include CYP119 (8-10), P450st (11), CYP174A1 (12), and CYP231A2 (13). The thermal stability of these enzymes makes them attractive starting points for the development of industrially useful catalysts. In this context, particular attention has also focused on CYP102 (P450BM3), a self-sufficient enzyme from Bacillus megaterium in which the flavoprotein protein required for transfer of electrons from NADPH is fused to the hemoprotein (14). The resulting simplicity and high catalytic rate have led to extensive efforts to engineer this protein for practical catalytic purposes (15-19). Although these proteins have properties that make them particularly attractive for engineering purposes, the large reservoir of P450 enzymes that collectively catalyze an astounding diversity of reactions suggests that P450 catalysis will develop into a highly useful technology.

The cytochrome P450 enzymes are defined by the presence in the proteins of a heme (iron protoporphyrin IX) prosthetic group coordinated on the proximal side by a thiolate ion (20, 21). This feature gives rise to the spectroscopic signature that defines these enzymes, as the thiolate-ligated ferrous-CO complex is characterized by a Soret absorption maximum at ∼450 nm (21). A thiolate-coordinated heme group is present in all P450 enzymes, although not all proteins with such coordination are members of this superfamily. One obvious exception, for example, is chloroperoxidase, which has a thiolate-coordinated heme group but normally catalyzes a very different reaction than the P450 enzymes (21-23).

Although there are unusual P450 enzymes, such as the thromboxane and prostacyclin synthases (24), or CYP152 from Sphingomonas paucimobilis or Bacillus subtilis (25, 26), that normally utilize peroxides as substrates, the defining reaction for P450 enzymes is the reductive activation of molecular oxygen. In this reaction, one of the oxygen atoms of molecular oxygen is inserted into the substrate and the other oxygen atom is reduced to a molecule of water. With one exception to date (27, 28), the electrons required for this reduction of molecular oxygen derive from reduced pyridine nucleotides (NADH or NADPH). The overall equation for the reaction thus adheres to the formula: RH + NAD(P)H + O2 + H+ -> ROH + NAD(P)+ + H2O, where RH stands for a substrate with a hydroxylatable site. P450 enzymes therefore belong to the monooxygenase class of enzymes that only insert one of the oxygen atoms of molecular oxygen into their substrates. However, under appropriate circumstances or with specific substrates, other P450-catalyzed reactions can be observed, including desaturation, carbon-carbon bond scission, and carbon-carbon bond formation (29, 30). This review specifically focuses on P450-catalyzed hydrocarbon hydroxylation, the reaction that is most characteristic of P450 enzymes and that has been most extensively investigated. However, the principles that apply in these reactions also apply to other hydroxylation reactions, including those that occur on carbons adjacent to nitrogen, sulfur, or oxygen.

Hydrocarbon hydroxylation by cytochrome P450 enzymes.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/S0014-5793%2898%2901705-0

Paul R. Ortiz de Montellano

Papers

Cytochrome P-450

Hydrocarbon hydroxylation by cytochrome P450 enzymes.

AMP-activated protein kinase phosphorylation of endothelial NO synthase

Endothelial nitric-oxide synthase : expression in escherichia coli, spectroscopic characterization, and role of tetrahydrobiopterin in dimer formation

Oxidizing species in the mechanism of cytochrome P450