Enzymes, catabolic

The isolate appears to produce the enzymes for the complete catabolism of lithocholic acid. However, in the presence of Pb2+ ions, some of these catabolic enzymes are inhibited, leading to the accumulation of partial breakdown products. It appears that enzymes involved in catabolism of the ring structure are more susceptable to inhibition by Pb2+ ions than are the enzymes involved in side chain catabolism. 

Prauinska, A. et ah. Chlorophyll breakdown in senescent Arabidopsis leaves Characterization of chlorophyll catabolites and of chlorophyll catabolic enzymes involved in the degreening reaction. Plant Physiol., 139, 52, 2005. 

The regulation of NCR-sensitive amino acid transporters in Saccharomyces cerevisiae has many points in common with that of catabolic enzymes. Amino acid permeases, as well as some other transporters of nitrogenous nutrients, are integrated into the regulatory circuits, both general and specific, which control catabolic processes. 

There may be a limiting substrate concentration required for induction of the appropriate catabolic enzyme. At low substrate concentrations the necessary enzymes wonld simply not be synthesized, and this could be the determining factor in some circumstances (Janke 1987). 

Induction of catabolic enzymes by growth with structurally unrelated substrates... 

The primary metabolism of an organic compound uses a substrate as a source of carbon and energy. For the microorganism, this substrate serves as an electron donor, which results in the growth of the microbial cell. The application of co-metabolism for bioremediation of a xenobiotic is necessary because the compound cannot serve as a source of carbon and energy due to the nature of the molecular structure, which does not induce the required catabolic enzymes. Co-metabolism has been defined as the metabolism of a compound that does not serve as a source of carbon and energy or as an essential nutrient, and can be achieved only in the presence of a primary (enzyme-inducing) substrate. 

A significant decrease in wakefulness with a concomitant increase in NREM sleep was also seen with systemic (20 mg/kg) or local application of a-FMH (50 pg in 1 pi) in the TMN region of cats. Although the sleep-inducing effect of a-FMH began 8 h after systemic administration and lasted for one day (Lin et at, 1988), the sleep-inducing effect appeared within 2 h of local application and its most prominent effect lasted for 9 h. In contrast, local microinjections of SKF-91488 (50 pg in 1 pi), a specific inhibitor of the catabolic enzyme HMT, produced an immediate increase in wakefulness, with a concomitant decrease in NREM and REM sleep that lasted for 6 h (Lin et at, 1986). 

The importance of adenosine deaminase in the duration and intensity of sleep in humans has been noted recently (Retey et al. 2005). Animal studies suggest that sleep needs are genetically controlled, and this also seems to apply in humans. Probably, a genetic variant of adenosine deaminase, which is associated with the reduced metabolism of adenosine to inosine, specifically enhances deep sleep and slow wave activity during sleep. Thus low activity of the catabolic enzyme for adenosine results in elevated adenosine, and deep sleep. In contrast, insomnia patients could have a distinct polymorphism of more active adenosine deaminase resulting in less adenosine accumulation, insomnia, and a low threshold for anxiety. This could also explain interindividual differences in anxiety symptoms after caffeine intake in healthy volunteers. This could affect the EEG during sleep and wakefulness in a non-state-specific manner. 

Finally, some neurotransmitters, like acetylcholine, are inactivated solely by a catabolic enzyme. Acetylcholinesterase rapidly breaks down the neurotransmitter to acetate and choline, and the choline is then actively transported into the presynaptic... 

Acetylcholinesterase The catabolic enzyme that rapidly terminates the physiological action of acetylcholine at synapses and neuroeffector junctions. 

Other leukodystrophies are associated with the lysosomal and peroxisomal disorders in which specific lipids or other substances accumulate due to a deficiency in a catabolic enzyme - for example Krabbe s disease, meta-chromatic leukodystrophy (MLD) and adrenoleuko-dystrophy (ALD) [1,2]. (These are discussed in detail in Ch. 40.) Similarly, disorders of amino acid metabolism can lead to hypomyelination - for example phenylketonuria and Canavan s disease (spongy degeneration) [1, 2, 25] (Ch. 40). The composition of myelin in the genetically... 

Catabolic enzyme NANA aldolase catalyses cleavage of NANA to form NAM and pyruvic acid, the latter being a more attractive material for a chemoenzymatic process. It has long been known that the reverse reaction may be used for NANA synthesis. However, this approach to a manufacturing process also has complications. 

Munch-Petersen, A., Nygaard, P., Hammer-Jespersen, K. and Fill, N., Mutants constitutive for nucleoside-catabolizing enzymes in Escherichia coli K 12. Eur. J. Biochem., 1972, 27, 208-215. 

Bogdanovic N, Bretillon L, Lund EG, Diczfalusy U, Lannfelt L, et al. 2001. On the turnover of brain cholesterol in patients with Alzheimer s disease. Abnormal induction of the cholesterol-catabolic enzyme CYP46 in glial cells. Neurosci Lett 314 45-48. 

A Hungarian research group reported on the hypotensive activity of 3-(pyrazol-l-yl)pyridazines of type (72) in rats [253-256]. The activity of these compounds (in which both of the hydrazino nitrogen atoms are incorporated into a five-membered aromatic ring system) has been found to be mediated by inhibition of prostaglandin-catabolizing enzymes. 

Specific structural features also determine the deactivation or destruction by catabolic enzymes of purine analogues. Selective destruction of these toxic materials may, in fact, be the sin e most important factor relating to their activity. 

Adenosine aminohydrolase (adenosine deaminase) is found in all types of cells and is apparently an important catabolic enzyme for the regulation of cellular metabolism. It has been isolated from a number of sources and the substrate specificities of the various enzymes are similar, since a low degree of specificity R... 

The literature on xanthine oxidase [84] and its companion catabolic enzyme uricase [87] has been extensively reviewed. Many purine analogues, with the exception of most 9-substituted purines [262], serve as substrates for xanthine oxidase both in vitro and in vivo, and if the product is a substrate for uricase, in species that possess this enzyme, the ultimate product is allantoin (LVIII). Thus 2-aminoadenine [5], A -methyladenine [122], and purine [129] are all catabolized... 

Monoamine oxidase inhibitors. The monoamine oxidase inhibitors (MAOIs) inhibit the intracellular catabolic enzyme monoamine oxidase. There are two types of monoamine oxidase MAO-A and MAO-B, both of which metabolize tyramine and dopamine. In addition, MAO-A preferentially metabolizes norepinephrine, epinephrine, and serotonin, and MAO-B preferentially metabolizes phenylethylamine (an endogenous amphetamine-like substance) and N-methylhistamine (Ernst, 1996). Some MAOIs are selective for A or B and some are nonselective (mixed). In addition, irreversible MAOIs (e.g., phenelzine, tranylcypromine) are more susceptible to the cheese effect than are the reversible agents (e.g., moclobemide). 

Inhibition of catabolic enzymes of GABA, and of protein kinase C signaling... 

Synthetic studies for sialic acid and its modifications have extensively used the catabolic enzyme N-acetylneuraminic acid aldolase (NeuA E.C. 4.1.3.3), which catalyzes the reversible addition of pyruvate (70) to N-acetyl-D-mannosamine (ManNAc, 11) to form the parent sialic acid N-acetylneuraminic acid (NeuSNAc, 12 Scheme 2.2.5.23) [1, 2, 45]. In contrast, the N-acetylneuraminic acid synthase (NeuS E.C. 4.1.3.19) has practically been ignored, although it holds considerable synthetic potential in that the enzyme utilizes phosphoenolpyruvate (PEP, 71) as a preformed enol nucleophile from which release of inorganic phosphate during... 

TGN represents the sum of 6-thioguanosine monophosphate (6-thio-GMP), -diphosphate (6-thio-GDP) and -triphosphate (6-thio-GTP). In contrast, both TPMT and XO are the predominant catabolic enzymes in the metabolism of thiopurines. TPMT catalyses the X-adenosyl-L-methionine dependent S-methylation of 6-MP and its metabolites into 6-methyl-mercaptopurine (6-MMP), 6-methyl-mercaptopurine ribonucleotides (6-MMPR) such as 6-methylthioinosine monophosphat (meTIMP), and 6-methyl-thioguanine nucleotides (6-MTGN) (93). 

The bioavailability of azathioprine (80%) is superior to 6-MP (50%). After absorption azathioprine is rapidly converted by a nonenzymatic process to 6-MP. 6-Mercaptopurine subsequently undergoes a complex biotransformation via competing catabolic enzymes (xanthine oxidase and thiopurine methyltransferase) that produce inactive metabolites and anabolic pathways that produce active thioguanine nucleotides. Azathioprine and 6-MP have a serum half-life of less than 2 hours however, the... 

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