Calcium complexes enzyme activator

The use of alkali and alkaline earth group metal ions, especially those of sodium, potassium, magnesium, and calcium, for maintenance of electrolyte balance and for signaling and promotion of enzyme activity and protein function are not discussed in this text. Many of these ions, used for signaling purposes in the exciting area of neuroscience, are of great interest. In ribozymes, RNAs with catalytic activity, solvated magnesium ions stabilize complex secondary and tertiary molecular structure. Telomeres, sequences of DNA at the ends of chromosomes that are implicated in cell death or immortalization, require potassium ions for structural stabilization. 

Magnesium is distinguished by the fact that it is required by most ATP-using enzymes. Here, Mg occurs as a complex with ATP, as shown in Figure 10,49. In other words, the true substrate for most ATF-requiring enzymes is not ATP, but the Mg-ATP complex. A deficiency in magnesium is uncommon. When it does occur, the physiological funchon that is most sensitive is neuromuscular activity. In molecular terms, the enzymes involved in neuromuscular activity that appear to be sensitive to Mg deficiency are those involved in the transport of sodium, potassium, and calcium, these enzymes are Na.K-ATPase and the calcium pump (Ca-ATPase). 

Other possible opiate activation sites could involve certain ATPases associated with calmodulin. A growing literature suggests that such Ca2+-dependent regulator proteins (calcium dependent regulator) regulate the activity of a number of enzymes such as phosphodiesterase (93) and adenylate cyclase (94) via the formation of Ca +-CDR -enzyme complexes in response to Ca + fluxes. Thus, they appear to represent a link between different types of cell messenger, namely Ca + and cAMP. It has further been postulated that calmodulin, a CDR protein, is a likely Ca + receptor site (95). These proteins may thus represent an important site for Ca +-opiate interactions, with consequent alteration of enzyme activity. 

Another theory is that calcium may not directly activate an enzyme to trigger secretion, but rather may first interact with a cytoplasmic protein, calmodulin. The calcium-calmodulin complex may then cause enzyme activation. The enzyme phosphodiesterase is known to be activated by such a calcium-calmodulin complex (26). 

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