Calcium inhibition

Peeraer, Y., Rabijns, A., Collet, J.-F., Van Scafdngen, E. and De Ranter, C. (2004) How calcium inhibits the magnesium-dependent enzyme human phosphoserine phosphatase, Eur. J. Biochem., 271, 3421-3427. 

Glucose isomerase has a higher pH optimum than is required in the preceding starch liquification and saccharification steps so that pH adjustment is necessary. Also the -amylase used to cany out saccharification requires calcium ions for full activity, but calcium inhibits glucose isomerisation, necessitating its removal by ion-exchange treatment prior to isomerisation. 

Ion Concentration. Heavy metals, particularly calcium, inhibit enzyme activity. The only feasible method of removing them is with ion exchange resins. 

A schematic representation of the cellular mechanisms through which agonists, such as dopamine, stimulate PTH release and calcium inhibits hormonal secretion is shown in Figure 11. In this schema, cAMP is a stimulatory second messenger while cytosolic calcium serves to inhibit hormone release by acting at several loci within the cell. The detailed molecular mechanisms through which cAMP and cellular calcium modulate cellular function remain to be determined. 

Inhibition of phosphodiesterase, causing elevation of intracellular platelet cyclicAMP and a consequent reduction in calcium inhibitions this platelet activation and granule releases... 

At micromolar concentration range, calcium enhances the integrin functions while calcium inhibits integrin fimction in the mM concentration range. Magnesium and manganese... 

At least part of the reason for these observations must be that precipitation is severely inhibited by organics such as humic acids (Berner et ai, 1978). Mitterer and co-authors (e.g., Mitterer and Cunningham, 1985) have explored the possible role of organic matter in cement formation. These authors suggested that, whereas some types of organic matter inhibit precipitation, other types, particularly those rich in aspartic acid, favor precipitation by complexing calcium. Inhibition of precipitation, coupled with slow transfer of fresh supersaturated seawater into sediment pores, seems to account for the lack of extensive early cementation. 

The parathyroid glands secrete parathyroid hormone (PTH), which regulates serum calcium levels. Decreased serum calcium stimulates the parathyroid glands to secrete parathyroid hormone. Increased serum calcium inhibits secretion of parathyroid hormone. 

A synthetic inhibitor of the regulatory domain of PKC, NPC 15437, has also been reported (Sullivan et al., 1992). Although lacking in potency (IC50 = 20 p.M), this peptide compound does not inhibit other kinases up to concentrations of 300 p-M. Mechanistically, this agent is a competitive inhibitor of phorbol ester activation (Kj = 5 xM) and phosphatidylserine activation (IC50 = 12 xM), and a mixed inhibitor to activation by calcium. Inhibition of PKC-mediated phosphorylation in platelets by NPC 15437 also occurs. 

ButterwOTlhlF, Zaloga GP, Prieli RC, Tucker WY, Royster RL. Calcium inhibits the cardiac stimulatingprDpertiesofdobutaminebutiKJtofamrinone. Chest( 9SC) 101,174-80. 

The hypothesis that calcium is crucially involved in the mechanism of action of vasopressin seems to be attractive for different reasons It has been known for long that calcium is very important for the permeability to water of a number of animal membranes (e. g. Fukuda 1935, Bozler 1959). It has been shown by Lassiter et al. (1965) that calcium inhibits the permeability to water in the distal part of the nephron but not in the more proximal parts where the hormone presumably does not act on the water permeability. It is known that calcium is crucial for the action of oxytocin on the uterus. The concentration of calcium is crucial for the inhibitory action of certain analogues of oxytocin (Rudinger 1964). 

Calcium inhibits the action of vasopressin on the equivalent pore radius of kidney slices from Necturus. 

Calcium inhibits the water uptake through intact frog skin. 

Necrosis is often initiated by damage to membranes, either the plasma membrane of the cell or the membranes of organelles, particularly mitochondria (Zimmerman, 1999). Cell membrane damage is often caused by membrane phospholipid peroxidation. Plasma membrane damage interferes wi ion regulation, calcium homeostasis, energy production, and decrease in the ability of that organelle to sequester calcium. Inhibition of protein synthesis is an alternative mechanism that may cause cell necrosis. Toxins that act in this way include phalloidin and related mushroom toxins, which inhibit the action of ribonucleic acid (RNA) polymerase, and therefore mRNA synthesis (Pineiro-Carrero and Pineiro, 2004). 

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