Esterases regulation

Chamay, D. Nari, J. Noat, G. 1992. Regulation of plant cell-wall pectin methyl esterase by polyamines -Interactions with the effects of metal ions. Eur. J. Biochem. 205 711-714. 

The alternative pathway may become activated by lipopolysaccharides, endotoxin (sepsis), virus, fungi, immunoglobulin A-antigen (IgA-Ag) immunocom-plexes, and foreign material. These activate C3, after which the common pathway of complement activation takes place (Fig. 4). There are also a number of inhibitors that regulate and control complement activation. The most important are the Cl-esterase inhibitor (Cl-Inh) and the membrane attack complex inhibitor factor (MACIF CD59). In sepsis a relative deficiency of Cl-Inh has been reported. Administration of Cl-Inh to patients with septic shock attenuates complement acti-... 

Esterases play a role in regulating the platelet-activating factor (PAF), a lipid with hypotensive properties [96], Phospholipase A2 (EC 3.1.1.4) is involved in this pathway by hydrolyzing a precursor to lyso-PAF and a free fatty acid. The activity of PAF, formed by acetylation of lyso-PAF, is controlled by an esterase hydrolyzing the acetate moiety [100]. 

The overall metabolism of vitamin A in the body is regulated by esterases. Dietary retinyl esters are hydrolyzed enzymatically in the intestinal lumen, and free retinol enters the enterocyte, where it is re-esterified. The resulting esters are then packed into chylomicrons delivered via the lymphatic system to the liver, where they are again hydrolyzed and re-esterified for storage. Prior to mobilization from the liver, the retinyl esters are hydrolyzed, and free retinol is complexed with the retinol-binding protein for secretion from the liver [101]. Different esterases are involved in this sequence. Hydrolysis of dietary retinyl esters in the lumen is catalyzed by pancreatic sterol esterase (steryl-ester acylhydrolase, cholesterol esterase, EC 3.1.1.13) [102], A bile salt independent retinyl-palmitate esterase (EC 3.1.1.21) located in the liver cell plasma hydrolyzes retinyl esters delivered to the liver by chylomicrons. Another neutral retinyl ester hydrolase has been found in the nuclear and cytosolic fractions of liver homogenates. This enzyme is stimulated by bile salts and has properties nearly identical to those observed for... 

Once the siderophore-iron complexes are inside the bacteria, the iron is released and utilized for vital cell functions. The iron-free hydroxamate siderophores are commonly re-excreted to bring in an additional iron load (Enterobactin is at least partially degraded by a cytoplasmic esterase This cycle is repeated until specific intracellular ferric uptake regulation proteins (Fur proteins) bind iron, and signal that the intracellular iron level is satisfactory, at -which point ne-w siderophore and siderophore-receptor biosynthesis are halted and the iron-uptake process stops. This intricate feedback mechanism allows a meticulous control over iron(III) uptake and accumulation against an unfavorable concentration gradient so as to maintain the intracellular iron(III) level within the required narrow window. Several excellent reviews concerning siderophore-iron transport mechanisms have been recently published i.3,i6, is,40,45,60-62 ... 

The specificity of blends of compounds used for pheromone communication by Lepidoptera species is the result of essentially two distinct sets of biosynthetic enzymes which regulate the production of specific olefinic bonds and synthesis of the oxygenated functional moiety, respectively. In Heliothis moths the regulatory systems that are responsible for production of the functional group during the final stages of pheromone biosynthesis consist of cellular acetate esterases and extracellular alcohol oxidases. Evidence indicates that the relative activities of these enzymes differ for each species of Heliothis. Thus, pheromone mediated reproductive isolation between closely related species of Heliothis is probably the result, in large measure, of the fact that some species require only aldehydes for communication while others use acetates, alcohols and aldehydes. 

A methylesterase which catalyzes the hydrolysis of y-glu-tamyl methyl esters of membrane bound proteins in Salmonella typhimurium and JJ. coli has recently been identified (25). Apparently, these membrane-bound proteins undergo methylation by a S-adenosylmethionine requiring methyltransferase (similar to transferase II). In this case the methylation and demethylation are directly associated with the chemotactic mobility of the microorganisms. When the cells are exposed to a chemotactic attractant, methylation of the membrane-bound proteins increases and straight-line movement up the gradient is induced. When the attractant is removed or a repellent substituted, the esterase decreases the methylation and random movement results. These control mechanisms are analogous in regulation to some of the reversible processes such as adenylation (26), uridylation (27) and phosphorylation (28). 

A CA epoxidase perhaps identical to the precocene epoxidase biosynthesizes Insect juvenile hormones (JH) from the analogous inactive oleflnic precursor, and the enzyme activity appears higher in precocene-sensitive species (32). Subsequent detoxification of JH occurs primarily by EHs and esterases in peripheral tissues, and preliminary information does not indicate major differences for JH degradation routes between chewing and sucking herbivores, or insect carnivores (33,34). More study of the role of detoxification in regulating the action of JH in target tissues is required. 

Aldridge and Reiner 1972). The A esterases have a serine catalytic site. The tertiary structure and amino acid sequences of several AChEs and BuChEs have been established (Taylor 1994). AChEs regulate excitation at cholinergic synapses, destroying the neurotransmitter ACh. AChE is one of the most active enzymes known, cycling within a few milliseconds (Taylor 1996). AChEs are found at synapses and neuromuscular junctions, and in central-nervous-system (CNS) neuron cell bodies, axons, muscles, red blood cells (RBCs), and platelets of ovine and rodent species (Silver 1974 Traina and Serpietri 1984 Hoffmann et al. 1989). 

Walker, C.H., Mackness, M.I. (1987). A esterases and their role in regulating the toxicity of organophosphates. Arch. Toxicol. 60 30-3. 

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