Rose R K, Dibdin G H, Shellis R P
MRC Dental Group, Dental School, Bristol, United Kingdom.
J Dent Res. 1993 Jan;72(1):78-84. doi: 10.1177/00220345930720011201.
By means of micro-equilibrium dialysis, calcium binding capacities and affinities were measured in three different oral bacteria, and the effects of extracellular polysaccharide, pH, and aggregation were investigated. Binding capacities of 31.0 +/- 2.1 (C. matruchotii), 34.7 +/- 3.7 (S. sanguis), and 41.5 +/- 5.4 (S. downei) mumol calcium/g wet weight of cells were found at pH 7.0, falling to 21.4 +/- 0.8 mumol calcium/g wet wt. cells at pH 5.0 for S. downei. Dissociation constants were found to vary between 0.78 +/- 0.24 and 1.77 +/- 0.30 mmol/L (at pH 7.0, depending on species), and between 0.62 +/- 0.04 and 1.77 +/- 0.30 (in the pH range 5.0 to 7.0, for S. downei only). Examination suggested that at pH 7.0 calcium-facilitated bacterial association occurs in the streptococci with calcium uptake curves analogous with those of positively cooperative systems. Desorption of calcium from aggregated S. downei suggested that the mechanism of desorption differed from that of uptake. This may be an important factor in plaque formation and in the binding of cells to the surface of formed plaque. Plaque calcium forms a reservoir, readily released by a pH drop, which may increase plaque fluid saturation and reduce demineralization.
通过微平衡透析法，测定了三种不同口腔细菌的钙结合能力和亲和力，并研究了细胞外多糖、pH值和聚集作用的影响。在pH 7.0时，发现变形链球菌的钙结合能力为31.0±2.1 μmol钙/克细胞湿重，血链球菌为34.7±3.7 μmol钙/克细胞湿重，唐氏链球菌为41.5±5.4 μmol钙/克细胞湿重；对于唐氏链球菌，在pH 5.0时，钙结合能力降至21.4±0.8 μmol钙/克细胞湿重。发现解离常数在0.78±0.24至1.77±0.30 mmol/L之间（在pH 7.0时，取决于细菌种类），以及在0.62±0.04至1.77±0.30之间（在pH 5.0至7.0范围内，仅适用于唐氏链球菌）。研究表明，在pH 7.0时，链球菌中发生钙促进的细菌聚集，其钙摄取曲线类似于正协同系统。从聚集的唐氏链球菌中解吸钙表明，解吸机制与摄取机制不同。这可能是牙菌斑形成以及细胞与已形成牙菌斑表面结合的一个重要因素。牙菌斑钙形成一个储备库，可通过pH值下降轻易释放，这可能会增加牙菌斑液饱和度并减少脱矿作用。
