Enzyme constitutive

A constitutive enzyme binding to caveolin-1 in the plasma membrane, mainly in endothelial cells. It is activated in the presence of Ca2+ and calmodulin. 

NOS (eNOS, NOS IH, NOS3). Classically, nNOS and eNOS were considered constitutive enzymes, whereas iNOS is cytokine-induced. Recent evidence suggests that nNOS and eNOS are also subject to important regulation of expression [1 ]. Within the human species, amino acid sequences of the three NOS isoforms share 52-58% identity. Each isoform is well conserved across mammalian species (>90% amino acid identity for nNOS and eNOS, >80% for iNOS). NOS enzymes exist in organisms as low as nematodes, protozoa, and even in plants (Fig. 1). 

Cyclooxygenase- lisa constitutive enzyme that converts arachidonic acid to prostaglandin H2 581... 

The alteration of hemoprotein(s) P-450 subpopulations in the rat may be observed spectrally, because after treatment of rats with polycyclic aromatic hydrocarbons, the Soret maximum of the carbonmonoxyferrocytochrome complex undergoes a hypsochromic shift from 450 to 448nm (50). This blue shift was not seen with rainbow trout hepatic microsomes (29,30). However, this does not preclude the induction of novel hemoproteins P-450 since (a) the induced hemoprotein(s) maty not differ spectrally from the constitutive enzymes and (b) the induced-hemoprotein may account for only a small proportion of total hemoprotein P-450, and hence its contribution to the position of the Soret maximum of carbon monoxide-treated reduced microsomes may be negligible. The latter suggestion is supported by the work of Bend et al. with the little skate. These workers have shown that hepatic microsomes from 1, 2,3,4-dibenzanthracene treated skates did not exhibit a hypsochromic shift when compared to control microsomes, however, partially purified hemoprotein exhibited an absorbance maxima at 448 nm (51). 

The enzymatic system participating in degradation of TNT or other nitroaromatics in plants has not yet been sufficiently characterised. Based on recent results, TNT is not metabolised by highly specific nitroreductases, which would be purposefully synthesized by plants, but by constitutive enzymes with nitroreductase activity (Nepovim 2005b). This assumption is in agreement with results presented by Ekman (2005) showed an increase of the expression of a couple of enzymes in root mRNA due to the induction caused by explosives. 

In Tabernaemontana divaricata treatment of plant cell suspension cultures with an elicitor cause inhibition of CS activity [24,25]. This response is accompanied by stimulation of activity of constitutive enzyme activities of the isoprenoid pathway leading to 2,3-oxidosqualene (squalene synthase and squalene oxidase), and induction of enzymes required for biosynthesis of pentacyclic triterpenoid phytoalexins (/lAS and aAS). Thus inhibition of the branchpoint enzyme CS results in increased flux through the triterpenoid pathway. 

Many pathological conditions, including ischemia/reperfusion, inflammation, and sepsis may induce tissues to simultaneously produce both superoxide and nitric oxide. For example, ischemia allows intracellular calcium to accumulate in endothelium (Fig. 20). If the tissue is reperfused, the readmission of oxygen will allow nitric oxide as well as superoxide to be produced (Beckman, 1990). For each 10-fold increase in the concentration of nitric oxide and superoxide, the rate of peroxynitrite formation will increase by 100-fold. Sepsis causes the induction of a second nitric oxide synthase in many tissues, which can produce a thousand times more nitric oxide than the normal levels of the constitutive enzyme (Moncada et al., 1991). Nitric oxide and indirectly peroxynitrite have been implicated in several important disease states. Blockade of nitric oxide synthesis with N-methyl or N-nitroarginine reduces glutamate-induced neuronal degeneration in primary cortical cultures (Dawson et al., 1991). Nitroarginine also decreases cortical infarct volume by 70% in mice subjected to middle cerebral artery occlusion (Nowicki et al., 1991). Myocardial injury from a combined hy-... 

There are cytosolic and membrane-bound isoforms of NO synthase. Certain soluble and particulate isoforms are constitutive and other soluble isoforms are inducible. The constitutive enzyme is, by definition, present in the catalytically active form and needs only to be stimulated by an appropriate chemical species, following which there is immediate formation of NO plus L-citrulline. This form of NO synthase requires calcium, and for the most part calmodulin, for stimulation of enzymatic activity. It is likely that an increase in intracellular free calcium in the presence of calmodulin is the signal for stimulation of NO synthase, and therefore, the production of NO. This view is consistent with the general understanding that, in vascular tissue, all endothelium-dependent vaso-... 

Lamas, S., Marsden, P. A., Li, G. K., Tempst, P., and Michel, T. (1992). Endothelial nitric oxide synthase Molecular cloning and characterization of a distinct constitutive enzyme isoform. Proc. Natl. Acad. Sci. U.S.A. 89, 6348-6352. 

Before discussing some of the observations concerning -NO in our laboratory, it is important to review a few of the basic principles of "NO production and mechanism of action. More detail on these topics can be found in other chapters in this book. First, "NO production can occur by one of two categories of NOS enzymes. Constitutive enzymes are expressed in various cell types, including endothelial cells, neurons, and neutrophils. Production of "NO by this type of enzyme is typically calcium/calmodulin-dependent and occurs immediately. This type of production has also been referred to as low output. Cells such as macrophages, hepatocytes, and smooth muscle cells express an inducible NO synthase. The induction of this enzyme typically results from exposure of the cells... 

Two actions of "NO had been well-described in other cell types. Induction of cGMP synthesis by "NO produced by the constitutive enzyme in the brain (Bredt et al., 1990) and endothelial cells (Ignarro et al., 1987) indicated that... 

Consensus sequences in DNA 265 Constitutive enzyme 538 Contact inhibition 573 of cells 29... 

A pure culture of the organism was inoculated into a basal medium with the addition of 0.025% caffeic acid. After 7 days incubation at 25°C under conditions of reduced oxygen tension, the caffeic acid was completely metabolized. Metabolites of caffeic acid are identified as dihydrocaffeic acid and ethyl catechol, respectively. In the 1960s, it has been reported that a constitutive enzyme present in strains of Aerobacter decarboxylates caffeic acid to 4-vinylcatechol nonoxidatively [20], Several cinnamic acids have been tested and the decarboxylation product from /7-coumaric acid has been identified as 4-vinylphenol. Thus, the bacterial enzyme activity requires a relatively unhindered 4-hydroxy group on the aromatic ring and an acrylic acid side chain. 

It has been established that some enzymes are produced only in the presence of their substrates and they are then said to be inducible. The quantity of such enzymes will vary considerably with changing environmental conditions. Other enzymes which are always detectable at constant levels, irrespective of nutrition and environmental conditions, are called constitutive enzymes. 

Constitutive enzymes. Enzymes synthesized in fixed amounts, regardless of growth conditions. 

The stimulation of the synthesis of the cellulase system of T. reesei QM 9414 by sophorose was established as shown by the results of experiments summarized in Table IV. Other than sophorose, of the glycosides and oligosaccharides tested, only lactose caused even a limited production of the enzymes of the cellulase system. Lactose is not as closely related structurally to sophorose as is, for example, the disaccharide laminaribiose it is more closely related structurally to cellobiose, which, despite being the major product of cellulose breakdown, does not promote enzyme production under the conditions of this experiment. It was noted that both intra- and extracellular constitutive enzyme levels produced by cells growing on glucose (or by resting cells without inducer, Table IV) are less than 0.5% of the fully induced levels and thus are negligible. 

In contrast to MT induction, the available evidence suggests that PC synthesis is not stimulated by direct transcriptional activation. PCs can be synthesised very rapidly (within 5 min) in response to metals entering the cells, even when protein synthesis is totally inhibited (Scheller et al., 1987 Robinson etal., 1988). Phytochelatin synthase thus appears to be a constitutive enzyme. Loeffler et al. (1989) have shown that, for the enzyme purified from Silene cucubalus, metal ion induction is a post-... 

L-Cysteine desulfhydrase in leaves of cucurbit plants is a constitutive enzyme whose activity can be enhanced by preincubation of leaf discs with L-cysteine, D-cysteine, or structural analogs of L-cysteine at millimolar concentrations preincubation with cystine does not affect the activity of the enzyme (20.261. Although the stimulation of L-cysteine desulfhydrase activity is... 

One of the most interesting things about human COX enzymes is that there is more than one of them—definitely two, and probably at least three. This is important to our understanding of the therapeutic effects of ibuprofen, aspirin, and acetaminophen. It had long been suspected that there was more than one COX enzyme, but it was not until 1991 that evidence for the existence of two forms, COX-1 and COX-2, materialized. It was then recognized that COX-1 is present at near constant levels in the body under all conditions (that is, it is a constitutive enzyme), whereas the levels of COX-2 could increase in response to inflammatory conditions (i.e., it is an inducible enzyme). This led to the idea that the side effects of ibuprofen and aspirin (including stomach ulcers) probably arose from inhibition of the constitutive COX-1 enzyme, whereas the therapeutic benefits arose from inhibition of the inducible COX-2 enzyme. 

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