Parvalbumins ions from

Dissociation or displacement of the two Ca2+ ions from parvalbumin occur at rates amenable to study by stopped-flow techniques. The kinetics of these reactions have generally been found to be biphasic, as for example in the displacement of Ca2+ by Yb3+ (507), or dissociation engendered by the addition of edta or egta (498,508) or of a fluorescent indicator (508). Fluorescent... 

Parvalbumin is a small (12 kDa), cytoplasmic, high-affinity, calcium-binding protein that has structural similarity to TnC and calmodulin. It is found especially in striated muscles in an amount proportional to their speed of relaxation. It acts as a calcium buffer, facilitating muscle relaxation by transferring calcium ions from TnC to the Ca-pump that sequesters calcium within the sarcoplasmic reticulum. Parvalbumin concentration in urine has been found to be increased with myotoxicity (Dare et al. 2002). 

Figure 2.11. The dependence of the position of the fluorescence spectrum maximum on excitation wavelength for tryptophan in a model medium (glycerol) at different temperatures (a) and singletryptophan proteins (b). 1, Whiting parvalbumin, pH 6.S in the presence of Ca2+ ions 2, ribonuclease Th pH 6.5 3, ribonuclease C2, pH 6.5 4, human serum albumin, pH 7.0, +10"4 M sodium dodecyl sulfate 5, human serum albumin, pH 3.2 6, melittin, pH 7.5, +0.15 M NaCl 7, protease inhibitor IT-AJ from Actinomyces janthinus, pH 2.9 8, human serum albumin, pH 7.0 9, -casein, pH 7.5 10, protease inhibitor IT-AJ, pH 7.0 11, basic myelin protein, pH 7.0 12, melittin in water. The dashed line is the absorption spectrum of tryptophan.

Such a decrease in the linewidth may result from a decrease in the Gd3+ coordination number upon formation of the macromolecular complex, which could result in greater symmetry and a lower zero-field splitting for the Gd3+ ion. This spectrum is independent of temperature between 4 and 25°C and is independent of the Gd3+/ ATPase ratio up to 2 Gd + ions/ATPase molecule. The peak-to-peak linewidth of 285 G sets a lower limit of 2,3 x 10"10s Qn the electron spin relaxation time of enzyme-bound Gd +t This symmetric, narrow EPR spectrum for the Gd3+-ATPase complex is compared in Figure 13B to that of Gd3+ bound to parvalbumin, a Ca2+-binding protein from carp. In this case, the spectrum is extremely broad and suggests a greatly distorted Gd3+ coordination geometry compared to the Ca2+-ATPase. 

Ahlstroem etal. (1987) described simulations for parvalbumin in vacuo and in a system with 2327 water molecules and three sodium ions for electroneutrality. The simulation with water differed less from the crystal structure than the in vacuo simulation. Large effects on dynamics were found for protein interior as well as surface atoms (Fig. 35). 

The function of parvalbumin has long been assumed to be that of buffering Ca in muscle cells, i.e., taking up Ca + ions released from Ca " "-troponin complexes, thereby ensuring that the cytoplasmic levels of free Ca + are always kept very low, even during short bursts of muscle activity.The widespread occurrence of parvalbumin in non-muscle tissue indicates that it probably has other roles as well. 

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