Ca" + /calmodulin -dependent protein

So far, it has been established from in vitro studies that the enzyme undergoes phosphorylation, a process that changes the conformation of the enzyme protein and leads to an increase in its activity. This involves Ca +/calmodulin-dependent protein kinase II and cAMP-dependent protein kinase which suggests a role for both intracellular Ca + and enzyme phosphorylation in the activation of tryptophan hydroxylase. Indeed, enzyme purified from brain tissue innervated by rostrally projecting 5-HT neurons, that have been stimulated previously in vivo, has a higher activity than that derived from unstimulated tissue but this increase rests on the presence of Ca + in the incubation medium. Also, when incubated under conditions which are appropriate for phosphorylation, the of tryptophan hydroxylase for its co-factor and substrate is reduced whereas its Fmax is increased unless the enzyme is purified from neurons that have been stimulated in vivo, suggesting that the neuronal depolarisation in vivo has already caused phosphorylation of the enzyme. This is supported by evidence that the enzyme activation caused by neuronal depolarisation is blocked by a Ca +/calmodulin protein kinase inhibitor. However, whereas depolarisation... 

Additional information <1> (no inhibition by specific inhibitors of protein kinases A or C and Ca /calmodulin dependent protein kinase) [2]... 

ATP -I- T-protein = ADP -I- 0-phospho-T-protein (activated by tubulin. Different from EC 2.7.1.123 Ca /calmodulin-dependent protein kinase not activated by calmodulin, cyclic nucleotides or Ca. Involved in the formation of paired helical filaments in brain. See comment on EC 2.7.1.37 protein kinase)... 

Soderling, T. R., 1999, The Ca-calmodulin-dependent protein kinase cascade, Trends Biochem Sci, 24, pp 232-6. 

Guo, T., Zhang, T., Mestril, R., Bers, D.M., 2006, Ca/Calmodulin-Dependent Protein Kinase II Phosphorylation of Ryanodine Receptor Does Affect Calcium Sparks in Mouse Ventricular Myocytes. Circ Res, 99(4), pp 398 106. 

Yuan, W., Bers, D.M. 1994, Ca-dependent facilitation of cardiac Ca current is due to Ca-calmodulin-dependent protein kinase. Am J Physiol. 267(3 Pt 2), pp H982-93. 

Clathrin assembly lymphoid myeloid lenkemia, as in CALM gene Calmodulin cell adhesion molecnle Ca +/calmodulin-dependent protein kinase... 

Koyama M, Spicer SS, Schulte BA. 1999. Immunohistochemical localization of Ca /Calmodulin-dependent protein kinase IV in outer hair cells. J HistochemCytochem 47 7-12. 

Sharp JW, Ross CM, Koehnle TJ, Gietzen DW. 2004. Phosphorylation of Ca /calmodulin dependent protein kinase type II and the a-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptor in response to a threonine-devoid diet. Neuroscience 126 1053-1062. 

Mishra-Gorur K, Singer HA, Castellot JJ Jr (2002) Heparin inhibits phosphorylation and autonomous activity of Ca /calmodulin-dependent protein kinase 11 in vascular smooth muscle cells. Am J Pathol 161 1893-1901... 

In brain, a large number of particulate soluble proteins are phosphory-lated in the presence of Mg " -ATP and Ca +—calmodulin. These phosphorylations can be blocked by phenothiazines and do not occur in the presence of cAMP or cGMP. Furthermore, they are unaltered by the Walsh inhibitor, which is specific for the cAMP catalytic subunit. Hence, investigators have concluded that there is present in both particulate and soluble fractions of brain a Ca " -calmodulin-dependent protein kinase that is insensitive to cyclic nucleotides and that contains its own set of protein substrates. A few reports have appeared in the literature claiming purification of a calcium-calmodulin-dependent kinase from mammalian brain. The en-... 

Long-term storage of information in Ca +-calmodulin-dependent protein kinase molecules [20]... 

Phospholamban is a homopentamer, each subunit consisting of 52 amino acids. The subunits consist of a 30-residue N-terminal hydrophilic region containing the phosphorylation sites, and a C-terminal hydro-phobic domain responsible for oligomerization and for anchoring phospholamban in the membrane. The N-terminal domain is a basic amphiphilic a-helix, which resembles the calmodulin-binding domain of many proteins (Chiesi efa/., 1991). Phospholamban is phosphorylated at serine-16 by cAK and cGK and at threonine-17 by Ca +/calmodulin-dependent protein... 

In isolated ER vesicles from smooth muscle, the addition of calmodulin induces a submaximal phosphorylation of phospholamban via an endogenous protein kinase (Raeymaekers and Jones, 1986). The addition of calmodulin does not, however, significantly stimulate the Ca2+ uptake in isolated ER vesicles (L. Raeymaekers, unpublished observations) or in skirmed smooth muscle cells (Stout and Silver, 1992). Since this lack of effect could be due to washout of the endogenous kinase, further experiments are needed using purified Ca +/calmodulin-dependent protein kinase. 

It was originally recognised by Dabrowska et al. (1978) that calmodulin was part of the active holoenzyme MLCK complex. The association of calmodulin with MLCK is rapid and appears to be diffusion limited. It could be described by a two-step process, a bimolecular step and an isomerisation (Torok and Trentham 1994). The time required for activating MLCK by Ca +/calmodulin may contribute to the latency of about 400-500 ms at 37 C which precedes increases in LC20 phosphorylation (Miller-Hance et al. 1988). The interaction of Ca Vcalmodulin with MLCK may be modulated by phosphorylation of MLCK. Purified MLCK is a substrate for protein kinase A (Conti and Adelstein 1981), the multifunctional Ca /calmodulin dependent protein kinase II (Hashimoto and Soderling 1990, Ikebe and Reardon 1990), protein kinase C (PKC) (Nishikawa et al. 1983) and mitogen activated protein kinase (MAP kinase, Klemke et al. 1997). Phosphorylation of MLCK by these protein kinases may alter the Ca -sensitivity of the enzyme and hence of contraction, as will be discussed below. 

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