Acetylations species differences

The product of the stoichiometric reaction of acetyl-P with ornithine, catalyzed by ornithine transcarbamylase, has been shown unequivocally to be 6-acetylornithine the transcarbamylases from rat liver, frog liver, and bacteria, however, even though yielding the same product, appear to differ in their ratios of activity with carbamyl-P and acetyl-P (Table n). While it is possible that the synthesis of 6-acetylornithine is catalyzed by other enzymes (16), the different ratios may be due to species differences we know now that the ratios of activity with carbamyl-P and acetyl-P of all ornithine transcarbamylases thus far tested remain constant with purification. Further, the ratio of citrulline to acetylornithine formation does not change with a number of treatments, such as heat inactivation of preparations containing orni-... 

Glucuronoxylan Even if hemicelluloses in various hardwood species differ from each other both quantitatively and qualitatively, the major component is an 0-acetyl-4-0-methylglucuronoi3-D-xylan, sometimes called glucuronoxylan. Often the xylose-based hemicelluloses in both softwoods and hardwoods are termed simply xylans. 

The promotional effect of the N(CH3)4 is rationalized differently. In this case, the cation is capable of generating N(CH3)3, which in turn can intercept the ruthenium-acetyl species to form iV-acetyl ammonium salts, for example,... 

Shinohara, A., Saito, K., Tamazoe, Y., Kamataki, T., and Kato, R., 1986, Acetyl coenzyme A dependent activation of N-hydroxy derivatives of carcinogenic arylamines Mechanism of activation, species difference, tissue distribution, and acetyl donor specificity. Cancer Res., 46 4362-4370. 

All known ACS enzymes are bifunctional in that they possess a C cluster with COdFI activity in addition to an A cluster (the ACS active site. Scheme 9). In the enzymes, a CO tunnel is described through which GO can pass directly from the C cluster, where it is generated from CO2, to the A cluster, where acetyl GoA synthesis takes place. Again, two mechanisms were proposed that differ in the order of binding events and redox states involved. In essence, however, GO binds to an Ni-GHs species, followed by insertion and generation of an Ni-acetyl species, which upon reaction with GoA liberates the acetyl GoA product. It is interesting to note that methylation of Ni occurs by reaction with methyl cobalamin (Scheme 7). In M. thermoacetica, the cobalamin is the cofactor for a rather unique protein called the corrinoid iron sulfur protein (GFeSP). The above process, even if mechanistic details still remain in question, resembles the industrial Monsanto acetic acid synthesis process (Scheme 9, bottom). In this case, however, the reaction is catalyzed by a low-valent Rh catalyst. 

Differences in the metabolic route between species are common, e.g., the rat mainly hydroxylates amphetamine leading to conjugated products whereas the rabbit and guinea pig (and man) mainly deamin-ate amphetamine. Acetylation of aromatic amines occurs in humans but not dogs while glucuronic conjugation is very poor in the cat. A good example of a compound that has the same routes of metabolism in different species but different rates is caffeine, as shown in Table 3. Species differences can be... 

Rat UP (70-90% of dose) in urine. Mouse (female) Conj. (60% of dose) neither glue, nor N-acetyl UP (25% of dose) in urine, unidentified metabolite (m) present. Species difference. Unusual conj. via unrecognized pathway. Non-microsomal metabolism. 

Acetic acid is a final product and the formation of CO2 does not occur through the oxidation of acetic acid, at least at room temperature (see Section 3.1). Instead, CO2 seems to be produced through the oxidation of acetaldehyde or an intermediate species likely an acetyl species. Moreover, CO2 is produced in amounts below 5% at room temperature although its production can increase at higher temperatures. COad and CH , ad species are the main adsorbed intermediates and these species mostly act as poison species wliich impede further adsorption and oxidation of ethanol. Moreover, the direct oxidation of ethanol or acetaldehyde to Cl species has also been proposed. As for the intermediates, the formation of COad and CH ad species have been identified unequivocally by a number of techniques such as EC-FTIR and Raman spectroscopy. The formation of acetyl (CH3CO) species has also been postulated, although its formation is still under debate. The scheme depicted in Figure 3.9 illustrates the different pathway for the oxidation of ethanol to different products and adsorbed species and the number of electrons involved in the individual pathways. 

There are a number of factors which can contribute to herbicide selectivity, including soil placement, rates of absorption and subsequent translocation, localization (both within the plant and at the subcellular level), and transformation to products of modified phytotoxicity. In addition, the recent work on the elucidation of the modes of action of the aryloxyphenoxypropionate and cyclohexanedione groups of herbicides has highlighted the importance of species differences in sensitivity of the target site, in this case the enzyme acetyl-CoA carboxylase. The monocot and dicot enzymes studied to date show a remarkable difference in sensitivity to these herbicides which correlates very well with the high level of resistance among dicots. Biotypes of Chenopodium album and Amaranthus hybridus L. resistant to atrazine as a result of a mutation in the 32-kDa protein component of photosystem II would constitute a further example. 

The observation of nitration at a rate independent of the concentration and the nature of the aromatic means only that the effective nitrating species is formed slowly in a step which does not involve the aromatic. The fact that the rates of zeroth-order nitration under comparable conditions in solutions of nitric acid in acetic acid, sulpholan and nitromethane differed by at most a factor of 50 indicated that the slow step in these three cases was the same, and that the solvents had no chemical involvement in this step. The dissimilarity in the rate between these three cases and nitration with acetyl nitrate in acetic anhydride argues against a common mechanism, and indeed it is not required from evidence about zeroth-order rates alone that in the latter solutions the slow step should involve the formation of the nitronium ion. 

The fermentative fixing of CO2 and water to acetic acid by a species of acetobacterium has been patented acetyl coen2yme A is the primary reduction product (62). Different species of clostridia have also been used. Pseudomonads (63) have been patented for the fermentation of certain compounds and their derivatives, eg, methyl formate. These methods have been reviewed (64). The manufacture of acetic acid from CO2 and its dewatering and refining to glacial acid has been discussed (65,66). 

The identification of a specific nitrating species can be approached by comparing selectivity with that of nitration under conditions known to involve the nitronium ion. Examination of part B of Table 10.7 shows that the position selectivity exhibited by acetyl nitrate toward toluene and ethylbenzene is not dramatically different from that observed with nitronium ion. The data for i-propylbenzene suggest a lower ortho para ratio for acetyl nitrate nitrations. This could indicate a larger steric factor for nitration by acetyl nitrate. 

A number of metal chelates containing transition metals in their higher oxidation states are known to decompose by one electron transfer process to generate free radical species, which may initiate graft copolymerization reactions. Different transition metals, such as Zn, Fe, V, Co, Cr, Al, etc., have been used in the preparation of metal acetyl acetonates and other diketonates. Several studies demonstrated earlier that metal acetyl acetonates can be used as initiators for vinyl polymeriza-... 

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