Sigma classes

Ji, X., von Rosenvinge, E.C., Johnson, W.W., Tomarev, S.I., Piadgorsky, J., Armstrong, R.N., and Gilliland, G.L. (1995) Three-dimensional structure, catalytic properties, and evolution of a sigma class glutathione transferase from squid, a progenitor of the lens S-crystallins of cephalopods. Biochemistry 34(16), 5317-5328. 

Wigneshweraraj, S.R., Fujita, N., Ishihama, A., and Buck, M. (2000) Conservation of sigma-core RNA polymerase proximity relationships between the enhancer-independent and enhancer-dependent sigma classes. EMBO J 19(12), 3038-3048. 

As shown by binding studies with 3H-PCP, some relationship exists between the hallucinogenic action of this drug and the sigma class of opiate receptors (131). Indeed, sigma opiates of the cyclazocine series are themselves potent... 

Meyer DJ, Thomas M (1995) Characterization of rat spleen prostaglandin H D-isomerase as a sigma-class GSH transferase. Biochem J 311 739-742... 

Kanaoka Y, Fujimori K, Kikuno R, Sakaguchi Y, Urade Y, Hayaishi 0. Structure and chromosomal localization of human and mouse genes for hematopoietic prostaglandin D synthase. Conservation of the ancestral genomic structure of sigma-class glutathione S-transferase. Eur J Biochem 2000 267 3315-3322. 

There are six major classes of the human cytosolic GST enzymes, namely, alpha, mu, omega, pi, theta, and the newly discovered zeta class (Mannervik et al., 2005). The sigma class is involved in prostaglandin metabolism (isomerization of PGH2 to PGD2) (Jowsey et al., 2001). Kappa class enzymes are expressed in... 

Because the psychotomimetic benzomorphans, classed as sigma opioids, inhibit binding of 3H-PCP and show PCP-like actions in several behavioral assays, it has been suggested that PCP and sigma opioids act through the same binding sites. However, recent work by a number of investigators (Su 1982 Tam 1983 Martin et al. 

The polysilanes are compounds containing chains, rings, or three-dimensional structures of silicon atoms joined by covalent bonds. Recently, polysilane high polymers have become the subject of intense research in numerous laboratories. These polymers show many unusual properties, reflecting the easy delocalization of sigma electrons in the silicon-silicon bonds. In fact, the polysilanes exhibit behavior unlike that for any other known class of materials. 

Attempts to synthesize transition metal alkyl compounds have been continuous since 1952 when Herman and Nelson (1) reported the preparation of the compound C H6>Ti(OPri)3 in which the phenyl group was sigma bonded to the metal. This led to the synthesis by Piper and Wilkinson (2) of (jr-Cpd)2 Ti (CH3)2 in 1956 and a large number of compounds of titanium with a wide variety of ligands such as ir-Cpd, CO, pyridine, halogen, etc., all of which were inactive for polymerization. An important development was the synthesis of methyl titanium halides by Beerman and Bestian (3) and Ti(CH3)4 by Berthold and Groh (4). These compounds show weak activity for ethylene polymerization but are unstable at temperatures above — 70°C. At these temperatures polymerizations are difficult and irreproduceable and consequently the polymerization behavior of these compounds has been studied very little. In 1963 Wilke (5) described a new class of transition metal alkyl compounds—x-allyl complexes,... 

Ri R2C=NR3 molecules represent another important class of Ri R2 AAR3 systems. In the parent system shown below the strength of the various sigma interactions varies in the order ... 

Molecular biology phorbol esters/Sigma 2000 diterp./carcinogens, NO promoters activators of protein kinase C pantrop. and tranpa te Euphorbiaceae, Ang. (also a standard for phorbol-class receptor in cancer studies)... 

There are various opioid receptors the three major classes of opioid receptors are mu (p), delta (5) and kappa (k) receptors. The p, receptor is the principal pain-modulating site in the CNS, mediating the action of morphine. There is considerable interest in the K receptor, which mediates a sedating analgesia with decreased addiction liability and respiratory depression and which allows for some structural flexibility. Unfortunately, the K receptor seems to be coupled to the sigma (a) receptor, which is implicated in psychotomimetic and dysphoric side effects. 

Perhaps the most significant reaction of this class to be discovered and characterized is the carbonyl insertion reaction (Equation 10) (15). As indicated, the methyl group (or other sigma-bonded organic group) is converted into an... 

In a cycloaddition reaction, two sigma bonds are formed to give a new ring of atoms, and one classification of these reactions is based on the number of ring atoms thal derive from each of the reacting units. One of the simplest classes are (2 + 2 cycloadditions, such as... 

Recent studies of polymeric Group IV catenates (in particular, polysilanes and polygermanes, la,b have demonstrated that there is significant sigma electronic delocalization along the polymer backbone which is responsible for many of the curious electronic properties of this class of materials [3]. 

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