Calcium hydrolytic reactions

Not all reactions involving water are classed as hydrolytic reactions. Thus the reaction of water with a molecule or ion such as calcium oxide... 

Figure 7, Phospholipase C-mediated hydrolysis of phosphatidyl inositol 4,5-bisphos-phate. Phosphoinositide-specific phospholipase C is activated during cellular stimulation and mediates the hydrolysis of phosphatidylinositol 4,5-bisphosphate. The two products of this reaction, DAG and IP3, are both intracellular second messengers. Thus, a single hydrolytic reaction initiates a bifurcating pathway of signal transduction mediated by protein kinase C activation and calcium mobilization, respectively.

Cowan Teeter (1944) reported a new class of resinous substances based on the zinc salts of dimerized unsaturated fatty acids such as linoleic and oleic acid. The latter is referred to as dimer acid. Later, Pellico (1974) described a dental composition based on the reaction between zinc oxide and either dimer or trimer acid. In an attempt to formulate calcium hydroxide cements which would be hydrolytically stable, Wilson et al. (1981) examined cement formation between calciimi hydroxide and dimer acid. They found it necessary to incorporate an accelerator, alimiiniiun acetate hydrate, Al2(OH)2(CHgCOO)4.3H2O, into the cement powder. 

These three catalytic functionalities are similar in practically all hydrolytic enzymes, but the actual functional groups performing the reactions differ among hydrolases. Based on the structures of their catalytic sites, hydrolases can be divided into five classes, namely serine hydrolases, threonine hydrolases, cysteine hydrolases, aspartic hydrolases, and metallohydrolases, to which the similarly acting calcium-dependent hydrolases can be added. Hydrolases of yet unknown catalytic mechanism also exist. 

The phosphoryl group of the intermediate can enter two different reaction pathways leading to its decomposition. The phosphoryl group can either be transferred to water or to ADP. The hydrolytic pathway leading to the liberation of phosphate must be coupled to calcium translocation as it infers from the fixed coupling between calcium accumulation and phosphate liberation. 

Potassium orthophosphates.—The normal salt, potassium orthophosphate, K3P04, is obtained by heating basic slag or native calcium phosphate with charcoal and potassium sulphate. The potassium sulphide simultaneously formed is converted into phosphate by addition of phosphoric acid, or the potassium phosphate is precipitated by addition of alcohol. The aqueous solution of the salt is very alkaline in reaction, owing to hydrolytic dissociation. The heat of formation from the elements in solution is 483-6 Cal.4... 

The hydrolytic ability of hydrochloric acid may be affected by salts present in the reaction mixture. The effect may be based on salting out of the hydrolysis products from the reaction mixture. For instance, magnesium and ammonium sulfates showed such an effect.117 Zinc and cadmium cations, as well as acetate and sulfate anions, decreased the hydrolysis rate with 0.1 M hydrochloric acid, whereas calcium, strontium, and barium ions exerted no effect.141 Neither copper metal, stainless steel, tin, nor sulfur dioxide impeded the hydrolysis with a solution of 0.03-0.05 M hydrochloric acid.142 There is a report143 that traces of metal salts affect the rate of hydrolysis but there are also contradicting findings144 145 that... 

The hydrolytic acidity is the ability of the soil to change the pH of salts split by hydrolysis. This represents the ability of the soil to bind a strong base and to release an equivalent amount of a weak acid. For determining the hydrolytic acidity, a salt of weak acid and strong base is used (sodium acetate or calcium acetate) the following reaction occurs ... 

In the presence of phosphate donating or accepting reactants, the translocation of calcium ions across the sarcoplasmic membranes is linked with phosphoryl transfer reactions leading to the phosphorylation of the transport protein. During calcium accumulation, the terminal phosphate group of ATP or of the other phosphate donors is rapidly transferred to the transport protein from which it is subsequently liberated by hydrolytic cleavage. The phosphoryl group in the protein is acid-stable and can therefore be stabilized in acidic quench media [112-114]. 

Chelate materials of this type are products of reaction of a metal base, such as calcium hydroxide or metal oxide, with weakly acidic organic substances with at least two functional groups. The ones used clinically are typically hydrolytically unstable, and this is responsible for their therapeutic effects. Ions released have beneficial properties, reducing inflanunation, being bacteriostatic and stimulating the odontoblasts to form secondary dentine. Ideally, calcium hydroxide chelates of this kind dissolve completely with time, and thus have the maximum possible therapeutic effect. 

Ionic calcium is essential for enzyme activity, both for hydrolytic and transphosphatidylation (see below) reactions EDTA inhibits the enzyme in crude extracts. The exact role of Ca has yet to be determined, but there seems little doubt that it is directly involved in the enzyme-phospholipid substrate interaction. 

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