Calcium as an activator

The contractile proteins of muscle were the first biological structure in which the role of ionized calcium as an activity-regulating agent was proved. Direct and indirect evidence has been furnished showing that the rapid activation and inactivation cycle of muscle depends on the sudden release of calcium ions and their subsequent complete removal. The quantities of calcium ions which have to be set free to cause the sudden start of chemical and mechanical activity are quite large, because the contractile proteins need for saturation the considerable quantity of approx. 0.2 jamol calcium/ml. Calcium depots with fairly high capacity on the one... 

The Immobili dEn me System. The glucose isomerases used are immobilized and granulated to a particle size between 0.3 and 1.0 mm. The enzyme granulates must be rigid enough to withstand compaction when they are packed iato the column. Ca " acts as an inhibitor in the system, and therefore calcium salts need to be removed from the feed symp. Conversely, Mg " acts as an activator, and magnesium salts are added to the feed symp. 

Fig. 7 Biosynthesis of NATs and TRP channel activation by NATs. (a) Evidence for a fatty acyl CoA taurine A-acyltransferase activity was detected in mouse tissue by incubating taurine and arachidonoyl-CoA with various tissue lysates, (b) arachidonyl NAT was tested as an activator of the TRPV1 (black line), TRPV4 (gray line), and TRPM8 (dashed line) ion channels. Channel activation was measured using a Fura-2-based calcium-imaging assay, where the ratio between the fluorescence at 340 and 380 nm is reflective of cellular calcium concentrations...

Diacylglycerol was mentioned as an activator of protein kinase C. In addition to diacylglycerol, protein kinase C is also activated by increased cellular calcium levels. Protein kinase C catalyzes, for example, the phosphorylation of G protein components the j8 subunit of the fiy complex and the a-GDP complex. Such phosphorylation apparently prevents the reassociation of the a-GDP with the fiy complex to give the G -GDP protein. It is thus clear that phosphorylation via protein kinase C participates in the regulation of G protein function. 

Ninety-nine percent of the calcinm and 85% of the phosphoms in the body are fonnd in bones, mostly a poorly crystalline hydroxyapatite Caio(P04)6(OH)2. In addition, calcium is involved in blood coagulation and is an intermediary factor between impulses and muscle contraction. Calcium has an activating effect on enzymes such as phosphorylase kinase and pyruvate dehydrogenase (lipoamide)-phosphatase. 

An antacid tablet containing calcium carbonate as an active ingredient required 24.5 mL of 0.0932 M HCl for complete neutralization. What mass of CaC03 did the tablet contain ... 

Silicsol is a commercial product introduced in Europe this past decade. It is described as an activated silica liquor with a calcium-based reagent. As opposed to sodium silicate (colloidal silica particles dispersed in soda), silicsol is claimed to be a true solution. Viscosity and penetrability are similar to sodium silicate, but the reaction is different, resulting in a stronger end product more resistant to creep. There is no syneresis associated with silicsol. 

Calcium is important in the growth of meristematic tissues including both shoot and root tips. It frequently accumulates in cell walls and leaves in the form of calcium pectate. Calcium also apparently acts as an activator for certain enzymes and performs other metabolic functions that are not yet clearly defined. It seems to neutralize to some extent the undesirable effects of nutrients in the plant that are either undesirable or absorbed in improper amounts or ratios. Too much calcium may, however, depress the uptake of potassium and magnesium, but unlike these elements it is comparatively immobile in the plant. 

C20H23N7O7, Mr 473.45, pale yellow crystals +3 H2O, mp. 248 -250 °C (decomp.), [a]n +16.8° (aqueous hydrogen carbonate). F. occurs in various microorganisms in which it acts as a growth factor e. g., for the lactic acid bacterium Leuconostoc citrovorum, therefore, it is also known as citrovorum factor. F. functions as an active 1-C unit (cf. folic acid) and formyl group transfer agent in the metabolism of folic acid tetrahy-drofolic acid. F. is accessible by synthesis and its calcium salt is used therapeutically as an antidote for folic acid antagonists such as methotrexate. 

Calcium plays multiple roles in plant physiology and a deficiency of calcium shows up early and in dramatic ways in plant appearance. Calcium is a constituent of cell walls in the form of calcium pectate. The middle lamella is composed mainly of calcium and magnesium pectates (56). Calcium also plays a role in the formation of cell membranes and lipid structures (57)- Calcium in small amounts is pecessary for normal mitosis and it also plays a role as an activator for numerous enzymes (58). Calcium is thought to play a role in carbohydrate translocation and somehow in the development of mitochondria (59). 

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