Low Affinity Calcium Binding

Binding class Number of bind- Association constant Hill 

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P. Kanellis, J. Yang, H. C. Cheung, and R. E. Lenkinski, Synthetic peptide analogs of skeletal troponin C Fluorescence studies of analogs of the low-affinity calcium-binding site II, Arch. Biochem. Biophys. 220, 530-540 (1983). 

N. A. Malik, G. M. Anatharamaiah, A. Gawish, and H. C. Cheung, Structural and biological studies on synthetic peptide analogues of a low-affinity calcium-binding site of skeletal troponin C, Biochim. Biophys. Acta 911, 221-230 (1987). 

Dang, C. V., Shin, C. K., Bell, W. R., Nagaswami, C., and Weisel, J. W. (1989). Fibrinogen sialic acid residues are low affinity calcium-binding sites that influence fibrin assembly./. Biol. Chem. 264, 15104-15108. 

The finding that S-100 appears largely confined to glia, coupled with its relatively low affinity calcium-binding make it appear unlikely that this protein is the neuronal calcium receptor of Katz and Miledi. 

The rapid calcium efflux efficiently decreases luminal calcium concentration, which induced acceleration of Ca -pump activity due to facilitation of calcium dissociation from a low affinity calcium-binding site (luminal site). To investigate the possible involvement of luminal calcium in the Ca pump stimulation, the luminal Ca concentration was indirectly manipulated by a Ca -ionophore and a calcium chelator (Figure 5). A23187 induced a five-fold increase in Ca pump activity [3] due to an increase of calcium permeability. Under this condition, Ca pump stimulation by flubendiamide was mostly eliminated [3], suggesting the involvement of luminal Ca in the Ca pump stimulation by flubendiamide. 

In contrast to the well established existence of external high-affinity calciumbinding sites the permanent presence of low-affinity sites in the molecule seems ambiguous. This uncertainty is inherent in the scheme used to describe the reaction sequence of phosphate transfer and calcium translocation (cf. [3,4]). In this scheme, low-affinity sites are assumed to result from the phosphorylation of the transport protein. The low-affinity calcium binding sites in the unphosphorylated protein are... 

The stimulatory effect of flubendiamide on the Ca pump was also diminished in the calcium buffers comprised of calcium chelators with high and low calcium affinity [3]. The low affinity calcium chelator, diBr-BAPTA (Kd = 3.7 pM), evidently accelerated the catalytic cycles of Ca pump as in the case with A23187. The result also implies importance of luminal calcium, since the low affinity of this chelator could not interrupt the calcium association with high affinity binding sites (cytoplasmic site) on Ca -ATPase. In addition, the results also demonstrate... 

Calcium and chloride cofactors have been shown to be needed for maximum rates of oxygen evolution [1,2]. The removal of calcium ions from PS2 has been linked to the loss of 17kDa and 23kDa extrinsic polypeptides. These polypeptides have been suggested to protect a high affinity calcium binding site. A low pH citrate wash has been used to remove one calcium per PS2 without loss of the extrinsic polypeptides [3]. 

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