Calcium complexes mammals

PDP is stimulated by calcium and magnesium. Like PDK, PDP is a dimer, but it is more loosely bound than the kinase to the complex. Mammals have two PDP isoforms, each of which contains both regulatory and catalytic subunits. PDP1 is highly expressed in cardiac and, to a lesser degree, skeletal muscle. PDP2 is present in both oxidative (heart, kidney) and lipogenic (liver, adipose) tissues. 

To understand the inhibition of a-amylase by peptide inhibitors it is crucial to first understand the native substrate-enzyme interaction. The active site and the reaction mechanism of a-amylases have been identified from several X-ray structures of human and pig pancreatic amylases in complex with carbohydrate-based inhibitors. The structural aspects of proteinaceous a-amylase inhibition have been reviewed by Payan. The sequence, architecture, and structure of a-amylases from mammals and insects are fairly homologous and mechanistic insights from mammalian enzymes can be used to elucidate inhibitor function with respect to insect enzymes. The architecture of a-amylases comprises three domains. Domain A contains the residues responsible for catalytic activity. It complexes a calcium ion, which is essential to maintain the active structure of the enzyme and the presence of a chloride ion close to the active site is required for activation. 

The concentration of calcium in the hlood plasma of most mammals and many vertebrates is quite constant al about 2.5 niM 110 milligrams pet 100 milliliters plasma). In the plasma, calcium exists in three forms ill as the tree ion. 12) bound to proteins, and t.l) complexed with organic te.g., citrate) or inorganic ie,g., phnsphatei acids. The tree ion accounts lor about 47.5% of the plasma calcium 46% is bound lo proteins and 6.5% is in complexed form. Of the latter, phosphate and citrate account for half. 

Calcium. Calcium, ihe most abundant mineral element in mammals, comprises 1.5-2.0 w1 G of Ihe adult human body, over 99 wt (i of which is present in bones nnd teeth. About 48 of scrum calcium is ionic, ca 46G is bound nr hlood proteins, the rest is present as diffusible complexes, e.g.. of citrate. The calcium ion level must he maintained within definite limits... 

Stimulus-evoked, calcium-dependent release of acetylcholine (ACh) from the cholinergic synapse normally occurs through the formation of a fusion complex between ACh-containing vesicles and the intracellular leaflet of the nerve terminal membrane (Amon et al., 2001). This synaptic vesicle fusion complex consists of several proteins of the SNARE family, including a 25 kDa synaptosomal associated protein (SNAP-25), vesicle-associated membrane protein (VAMP, or synaptobrevin), and the synaptic membrane protein syntaxin. Other SNARE proteins have been identified as components of membrane transport systems in yeast and mammals but have not been implicated as targets for BoNTs. Meanwhile, type A and E neurotoxins cleave SNAP-25 while types B, D, F, and G act on VAMP and type C1 toxin cleaves both syntaxin and SNAP-25. Neurotoxin-mediated cleavage of any of these substrates disrupts the processes involved in the exocytotic release of ACh and leads to flaccid paralysis of the affected skeletal muscles. 

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