Enzymes calcium activation

This calcium-activated enzyme [EC 3.4.21.75] catalyzes the hydrolysis of peptide bonds in protein precursors that results in the release of mature proteins from their proproteins by hydrolysis of ArgXaaYaaArg—Zaa bonds, where Xaa can be any amino acid and Yaa is an arginyl or a lysyl residue. Albumin, complement component C3, and von Willebrand factor are thus released from their respective precursors. Furin is a member of the peptidase family S8. 

It was very early recognized that the calcium transport and the calcium-dependent ATPase could simultaneously be blocked by thiol reagents26). In contrast to various other thiol containing enzymes the activities of the sarcoplasmic reticulum membranes cannot be restored when the blocking agents are removed. 

FIGURE 10—29. Cellular events occurring during excitotoxicity (part 3). Once excessive glutamate causes too much calcium to enter the neuron and calcium activates dangerous enzymes, these enzymes go on to produce troublesome free radicals. Free radicals are chemicals that are capable of destroying other cellular components, such as organelles and membranes, by destructive chemical reactions. 

This obvious dependence on extracellular calcium is somewhat unexpected because (1) the sustained enhancement of calcium influx rate is adequately balanced by an increase in calcium efflux rate so that (2) the calcium concentration in the bulk cytosol is maintained near the basal value. This apparent paradox may be resolved by a model [54] which postulates that during the sustained phase of cellular response the high rate of calcium cycling across the plasma membrane raises the calcium concentration in a region just below the plasma membrane, often called the submembrane domain (see Rasmussen and Barrett, Chapter 4). Because the elevated calcium level in this domain is not conducted into the bulk cytosol, it cannot activate calcium-dependent response elements in the cytosol. Rather it regulates the activity of calcium-sensitive, plasma membrane-associated enzymes such as the calcium pump and PKC, the previously described phospholipid-dependent, calcium-activated protein kinase. 

Elevated cytoplasmic calcium activates a variety of enzymes with membrane damaging effects. The major enzymes that are involved in activation by calcium include... 

CALCIUM The most abundant of the body s minerals an important component of bones and teeth important participant in regulation of many metabolic processes. When bound to the regulatory protein calmodulin, calcium helps modulate the activities of many enzymes. Calcium is important for blood clotting, neural and muscular activity, cell motility, hormone actions, and other activities. 

Calcium Activates the Regulatory Protein Calmodulin, Which Stimulates Many Enzymes and Transporters... 

Deodorant A cAMP phosphodiesterase has been discovered that is found predominantly in olfactory sensory neurons (Yan et al., 1995, Proc. Natl. Acad. Sci. 10 9677). The enzyme is activated by Ca2+. What do you think this enzyme does, and why do you think it is regulated by calcium (Hint Study the response and recovery animations in the Conceptual Insights module on signaling pathways.)... 

Another aspect of heating soybeans in particular is the impact on the phospholipase enzyme. The phospholipase enzyme is activated at approximately 55°C and remains activated up to approximately 100°C. In this temperature range, and with sufficient exposed surface area and time, the phospholipase enzyme modifies a portion of the phospatides in the oil fraction by splitting off the non-fatty acid moiety (16). The resultant calcium and magnesium salts of phosphatidic acids that are formed tend to be more oil-soluble than water-soluble, thereby converting phospatides from a hydratable form to a nonhydratable form (16). This has a resultant impact on the quantities of acid, caustic and silica needed to reduce the phosphorus content of the soybean oil in the downstream degumming and refining unit operations. 

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