Calcium enzyme cofactor

Enzyme active sites, 136,148, 225. See also Protein active sites in carbonic anhydrase, 197-199 in chymotrypsin, 173 in lysozyme, 153, 157 nonpolar (hypothetical site), 211-214 SNase, 189-190,190 steric forces in, 155-158, 209-211, 225 in subtilisin, 173 viewed as super solvents, 227 Enzyme cofactors calcium ... 

The different pro- and anticoagulatory systems are complex regulated cascades involving blood cells (platelets, monocytes, endothelial cells), enzymes, cofactors, phospholipids, and calcium, which interact with each other... 

This enzyme [EC 2.7.1.127], also referred to as lo-myo-inositol-trisphosphate 3-kinase, catalyzes the reaction of ATP with iD-myo-inositol 1,4,5-trisphosphate to produce ADP and iD-myo-inositol 1,3,4,5-tetrakisphos-phate. The enzyme requires calcium ions as a cofactor. 

Pharmacology Calcium is essential for the functional integrity of the nervous and muscular systems, for normal cardiac contractility and the coagulation of blood. It also functions as an enzyme cofactor and affects the secretory activity of endocrine and exocrine glands. 

Calcium-binding Proteins Copper Enzymes in Denitrification Copper Proteins with Type 1 Sites Copper Proteins with Type 2 Sites Iron Heme Proteins Electron Transport Iron-Sulfin Proteins Metal-mediated Protein Modification Metallochaperones Metal Ion Homeostasis Molybdenum MPT-containing Enzymes Nickel Enzymes Cofactors, Nitrogenase Catalysis Assembly Zinc Enzymes. 

During blood coagulation either an intrinsic (all blood) system or an extrinsic (tissue juice-lipoprotein) system is activated.. In either case the pathways meet at the activation of Factor X, forming a proteolytic enzyme Factor X. This enzyme in the presence of cofactors (calcium ion, phospholipid and Factor V) will form thrombin from prothrombin. Heparin is a cofactor for a protein called antithrombin III which circulates in the plasma and is an inhibitor of both Factor Xg and thrombin. Antithrombin III neutralizes these 2 enzymes by molecular combination heparin increases the rate of this neutralization. In the past 2 years work has continued on the mechanism of blood coagulation More... 

In the EHE process, a starch slurry is prepared and calcium, as the chloride or hydroxide, is added as a cofactor to provide heat stabiUty to the enzyme. The starch slurry is passed through a stream injection heater and held at temperature for about one hour. The resulting 4—8 DE hydrolyzate is then subjected to a heat treatment in a hoi ding tube, redosed with enzyme, and allowed to react for one hour to a DE level of 10—15. 

HES is produced from 93—96% dextrose hydrolyzate that has been clarified, carbon-treated, ion-exchanged, and evaporated to 40—50% dry basis. Magnesium is added at a level of 0.5—5 mAf as a cofactor to maintain isomerase stabiUty and to prevent enzyme inhibition by trace amounts of residual calcium. The feed may also be deaerated or treated with sodium bisulfite at a level of 1—2-mAf SO2 to prevent oxidation of the enzyme and a resulting loss in activity. 

Calcium important cellular cation cofactor for some enzymes important in enzyme stability. 

Vitamin K is the cofactor for the carboxylation of glutamate residues in the post-synthetic modification of proteins to form the unusual amino acid y-carboxygluta-mate (Gla), which chelates the calcium ion. Initially, vitamin K hydroquinone is oxidized to the epoxide (Figure 45-8), which activates a glutamate residue in the protein substrate to a carbanion, that reacts non-enzymically with carbon dioxide to form y-carboxyglut-amate. Vitamin K epoxide is reduced to the quinone by a warfarin-sensitive reductase, and the quinone is reduced to the active hydroquinone by either the same warfarin-sensitive reductase or a warfarin-insensitive... 

NO is a gaseous neurotransmitter implicated in signaling in the central and peripheral nervous system as well as in the immune system and the vasculature. NO is formed from L-arginine by nitric oxide synthase (NOS). There are three isoforms of NOS. All isoforms require NADPH as a cofactor, use L-arginine as a substrate, and are inhibited by Nw-nitro-L-arginine methyl ester (L-NAME). The three isoforms are separate gene products. One isoform of NOS is a cytosolic, calcium/calmodulin-independent, inducible enzyme (iNOS). It is found in macrophages, neutrophils, vascular smooth muscle, and endothelia. The iNOS... 

LO activity is found in a variety of mammalian cells, most notably leukocytes, with the enzymes from neutrophils and the rat basophilic leukemia (RBL-1) cell line being the most studied several have been purified and cloned [5]. 5-LO is a cytosolic enzyme which requires calcium, ATP and additional uncharacterized cell components for optimal activity. Characterization and kinetic studies with 5-LO enzymes are often difficult, because of self-inactivation and complex cofactor requirements. 

In addition to its role as a bone component, calcium functions as a signaling substance. Ca "" ions act as second messengers in signal transduction pathways (see p. 386), they trigger exocytosis (see p. 228) and muscle contraction (see p. 334), and they are indispensable as cofactors in blood coagulation (see p. 290). Many enzymes also require Ca "" for their activity. The intracellular and extracellular concentrations of Ca "" are strictly regulated in order to make these functions possible (see B, C, and p.388). 

The last column in the table lists some of the functions of minerals. It should be noted that almost all of the macroelements in the body function either as nutrients or electrolytes. Iodine (as a result of its incorporation into iodothyronines) and calcium act as signaling substances. Most trace elements are cofactors for proteins, especially for enzymes. Particularly important in quantitative terms are the iron proteins hemoglobin, myoglobin, and the cytochromes (see p. 286), as well as more than 300 different zinc proteins. 

Mammalian Cell Protease Inhibitor CocktaiL These should contain AEBSF, pepstatin A, E-64, bestatin, leupeptin, and aprotinin. (Metal chelators can be added to suppress the activity of calcium ion-dependent proteases such as calpain. Again, one must determine whether the protein or enzyme being purified does not require a divalent metal cofactor for stabihty or activity.)... 

Several mechanisms have been postulated to account for thallium s toxicity, including ligand formation with sulfhydryl groups of enzymes and transport proteins, inhibition of cellular respiration, interaction with riboflavin and riboflavin-based cofactors, alteration of the activity of K -dependent proteins, and disruption of intracellular calcium homeostasis. ... 

P3. Posner, I., and Morales, A., Mechanisms of enzyme and substrate activation by lipoprotein lipase cofactors. I. A specific requirement of physiological concentrations of calcium for enzyme activity. J. Biol. Chem. 247, 2255-2265 (1972). 

Some elements are essential to the composition or function of the body. Since the body is mostly water, hydrogen and oxygen are obviously essential elements. Carbon (C) is a component of all life molecules, including proteins, lipids, and carbohydrates. Nitrogen (N) is in all proteins. The other essential nonmetals are phosphorus (P), sulfur (S), chlorine (Cl), selenium (Se), fluorine (F), and iodine (I). The latter two are among the essential trace elements that are required in only small quantities, particularly as constituents of enzymes or as cofactors (nonprotein species essential for enzyme function). The metals present in macro amounts in the body are sodium (Na), potassium (K), and calcium (Ca). Essential trace elements are chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), copper (Cu), zinc (Zn), magnesium (Mg), molybdenum (Mo), nickel (Ni), and perhaps more elements that have not yet been established as essential. 

However, EGTA does not diminish adenylate cyclase activity this suggests that calcium (and by inference calmodulin) may not be an important cofactor for this enzyme in the bovine parathyroid gland (E.M. Brown and B. Dawson-Hughes, unpublished observations). 

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