Properties calmodulin

In addition, vinpocetine selectively inhibits a specific calcium, calmodulin-dependent cycHc nucleotide phosphodiesterase (PDF) isozyme (16). As a result of this inhibition, cycHc guanosine 5 -monophosphate (GMP) levels increase. Relaxation of smooth muscle seems to be dependent on the activation of cychc GMP-dependent protein kinase (17), thus this property may account for the vasodilator activity of vinpocetine. A review of the pharmacology of vinpocetine is available (18). 

The synthesis of 5-HT can increase markedly under conditions requiring more neurotransmitter. Plasticity is an important concept in neurobiology. In general, this refers to the ability of neuronal systems to conform to either short- or long-term demands placed upon their activity or function (see Plasticity in Ch. 53). One of the processes contributing to neuronal plasticity is the ability to increase the rate of neurotransmitter synthesis and release in response to increased neuronal activity. Serotonergic neurons have this capability the synthesis of 5-HT from tryptophan is increased in a frequency-dependent manner in response to electrical stimulation of serotonergic soma [7]. The increase in synthesis results from the enhanced conversion of tryptophan to 5-HTP and is dependent on extracellular calcium ion. It is likely that the increased 5-HT synthesis results in part from alterations in the kinetic properties of tryptophan hydroxylase, perhaps due to calcium-dependent phosphorylation of the enzyme by calmodulin-dependent protein kinase II or cAMP-dependent protein kinase (PKA see Ch. 23). 

K. P. Kohse and L. M. Heilmeyer, The effects of Mg2+ on the Ca2+-binding properties and Ca2 +-induced tyrosine-fluorescence changes of calmodulin isolated from rabbit skeletal muscle, Eur. J. Biochem. 117, 507-513 (1981). 

Calcium effects. The biochemical effects of Ca "" in the cytoplasm are mediated by special Ca -binding proteins calcium sensors"). These include the annexins, calmodulin, and troponin C in muscle (see p. 334). Calmodulin is a relatively small protein (17 kDa) that occurs in all animal cells. Binding of four Ca "" ions (light blue) converts it into a regulatory element. Via a dramatic conformational change (cf 2a and 2b), Ca -calmodulin enters into interaction with other proteins and modulates their properties. Using this mechanism, Ca "" ions regulate the activity of enzymes, ion pumps, and components of the cytoskeleton. 

PHYTOTOXIC COMPOUNDS WITH CALMODULIN INHIBITOR PROPERTIES FROM SELECTED MEXICAN FUNGI AND PLANTS... 

Phytotoxic Compounds with Calmodulin Inhibitor Properties 429... 

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