Specificity intermediates

CycIohexanediamine s commercial origin is its presence as a minor 0.1 <1% coproduct of hexamethylenediamine [124-09-4] produced by hydrogenation of adiponittile [111-69-3]. Fractional distillation by up to four columns in a series is routine commercial practice to purify nylon grade acychc diamine the cmde cycloahphatic diamine requires further refining before use as a specification intermediate. 

Non-reactive ion-exchange resin. Commonly employed at a specific intermediate density to separate cation and anion resins in a mixed-bed demineralization plant, in order to limit contaminant leakage, especially from regenerants. 

In maize, many phenotypic mutants have been associated with cloned genes by a combination of HPLC analysis of specific intermediate metabolite accumulation, RT-PCR and immunolocalization of candidate genes, and recombinant inbred mapping of candidate cDNAs. Psyl was cloned by transposon tagging and later shown to be functional in the color complementation system and to be the specific... 

The remaining six disorders are due to defects of enzymes involved specifically in the synthesis of cholesterol (Fig. 5.1.2). The detection of specific intermediate sterol species in cells, tissues, and/or body fluids of patients suspected to suffer from a defect in cholesterol biosynthesis based on their clinical presentation is often the first line of diagnosis, which can then be followed by enzyme and/or molecular diagnostic testing [9]. 

T Given that many amino acids are either neurotransmitters or precursors or antagonists of neutrotransmitters, genetic defects of amino acid metabolism can cause defective neural development and mental retardation. In most such diseases specific intermediates accumulate. For example, a genetic defect in phenylalanine hydroxylase, the first enzyme in the catabolic pathway for phenylalanine (Fig. 18-23), is responsible for the disease phenylketonuria (PKU), the most common cause of elevated levels of phenylalanine (hyperphenylalaninemia). 

Kim, P. S. and Baldwin, R. L. 1982. Specific intermediates in the folding reactions of small proteins and the mechanism of protein folding. In Annual Review of Biochemistry, Vol. 51. E.S. Snell, P. D. Boyer, A. Meister and C.C. Richardson (Editors). Annual Reviews, Palo Alto, Calif., pp. 459-489. 

The Batcho-Leimgruber indole synthesis is probably the most important and widely used method for the preparation of lH-2,3-unsubstituted indoles. In an attempt to extend the utility of the process to the preparation of 3-substituted indoles, functionalisation of the specific intermediate enamine 1 was explored. Treatment of 1 with ethyl chloroformate in refluxing chloroform in the presence of AT,JV-diethylaniline failed to give the expected ester. Instead, a product was obtained the spectral data for which suggested that it was a dienamine. The same product could be obtained in 52% yield simply by treatment of 1 with half an equivalent of TsOH in toluene at 90°C, and catalytic hydrogenation of this dienamine gave 2 in 58% yield. 

Another example of a dispersion of SWCNTs in a multi-component antiferro-electric smectic-C liquid crystal mixture was shown by Lagerwall and Dabrowski et al. [497]. In this study, SWCNTs caused the appearance of a single-layer SmC phase between the SmA phase and the crystalline state in comparison to the non-doped sample exhibiting an SmA and two specific intermediate phases, an SmC p and an SmC Y phase. 

Whereas several transient species have been observed for dioxygen activation by MMOH, no intermediates were found by rapid-mixing spectroscopic methods for the actual methane hydroxylation step. Mechanistic probes, i.e. certain non-natural substrates that are transformed into rearranged products only if the reaction proceeds via a specific intermediate such as a radical or a cation, give ambivalent results Some studies show that products according to a pathway via cationic intermediates are obtained in sMMO hydroxylations and at least one study suggests the presence of a radical intermediate [40]. Computational analyses of the reaction of MMOHq with methane suggest a so-called radical recoil/rebound mechanism in which MMOHq... 

Meng, J.J., Bomslaeger, E. A., Green, K. J., Steinert, P. M., and Ip, W. (1997). Two hybrid analysis reveals fundamental differences in direct interactions between desmoplakin and cell type specific intermediate filaments. /. Biol. Chem. 272, 21495-21503. 

Typical reactions of cellulose, such as oxidation or chain cleavage, can be caused by many different reagents and conditions. It will thus be difficult to relate the reaction outcome to the presence of a specific intermediate. 

Overall Catalytic Cycle with Specific Intermediates... 

Figure 9.2. Metabolism of pyrrolizidine alkaloids (PAs) in Senecio vernalis. The substrates for alkaloid biosynthesis, putrescine and spermidine, are derived from primary metabolism. Homospermidine, synthesized by homospermidine synthase (HSS), is the first pathway specific intermediate. It is exclusively incorporated into the necine base moiety of senecionine A-oxide, the backbone structure of all PAs found in this Senecio species. During allocation from the roots as site of synthesis to the shoots, it is chemically modified to provide the species specific PA-pattem.

Biosynthesis of IAA from tryptophan uses the L-form of the amino acid.75 Some of the enzymes that catalyze the conversion of specific intermediates have been identified, and some of the genes coding for the enzymes have been cloned. Such findings establish that plants are competent to carry out such metabolic conversions however, the specific involvement of these genes and intermediates requires confirmation, because biochemical studies carried out with applications to tissue segments or with extracts could disrupt tissue and cellular compartmentalization and because enzymes that catalyze the conversion of tryptophan to IAA in vitro may never come into contact with the intermediates in vivo. Thus, the physiological relevance of some of these pathways remains an open question.69 An additional concern is that many of the enzymes have wide substrate specificities, so it has been difficult to implicate them solely in IAA biosynthesis. Some of the intermediates and enzymes that have been described to have the competence to carry out these reactions are discussed below. 

Unfortunately diacetyl formation is still not well understood. Acetoin formation occurs either by nonspecific interaction of acetaldehyde with the a-hydroxyethyl thiamine pyrophosphate intermediate in pyruvate decarboxylation (209) or by decarboxylation of a-acetolactate (210), which in turn arises either from interaction of pyruvate with a-hydroxyethyl thiamine pyrophosphate (211) or as a specific intermediate in valine biosynthesis (212, 213). Diacetyl does not appear to be formed directly from acetoin (208, 214). It is formed from a-acetolactate, in absence of cells, by O2 oxidation (215), and even under N2 (216), although an oxidation must occur. It is also formed from acetyl CoA (217, 218), probably by interaction with a-hydroxyethyl thiamine pyrophosphate [cf. stimulation by acetyl CoA addition to a solution of pyruvate and pyruvate decarboxylase (2i5)]. It is not known whether this involves a specific enzyme or is a mere side reaction. 

At One time it was thought that women taking oral contraceptives were at risk for B deficiency. This notion seem-S to have been in error. The error was due to a misinterpretation of the tryptophan load lest. As mentioned earlier, a deficiency in vitamin B(,can induce the accumulation of specific intermediates of the tryptophan catabolic pathway and enhanced excretion in the urine. Oral contraceptives can also induce ar increase in the formation and excretion of specific intermediates by stimulating the activity of specific enzymes of the tryptophan catabolic pathway, This stimulation was responsible for the false indications of deficiency. Independently of the tryptophan load test, there continues to be some evidence for risk associated with the use of oral contraceptives. Oral contraceptive use may result in lowered levels of plasma vitamin Bf, Tlicsc lowered levels may result in a vitamin deficiency when coupled with pregnancy and lactation. 

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