Marquis R E
J Bacteriol. 1973 Dec;116(3):1273-9. doi: 10.1128/jb.116.3.1273-1279.1973.
Immersion-refractometric and light-scattering measurements were adapted to determinations of average refractive indices and physical compactness of isolated bacterial cell walls. The structures were immersed in solutions containing various concentrations of polymer molecules that cannot penetrate into wall pores, and then an estimate was made of the polymer concentration or the refractive index of the polymer solution in which light scattering was reduced to zero. Because each wall preparation was heterogeneous, the refractive index of the medium for zero light scattering had to be estimated by extrapolation. Refractive indices for walls suspended in bovine serum albumin solutions ranged from 1.348 for walls of the rod form of Arthrobacter crystallopoietes to 1.382 for walls of the teichoic acid deficient, 52A5 strain of Staphylococcus aureus. These indices were used to calculate approximate values for solids content per milliliter, and the calculated values agreed closely with those estimated from a knowledge of dextran-impermeable volumes per gram, dry weight, of the walls. When large molecules such as dextrans or serum albumin were used for immersion refractometry, the refractive indices obtained were for entire walls, including both wall polymers and wall water. When smaller molecules that can penetrate wall pores to various extents were used with Micrococcus lysodeikticus walls, the average, apparent refractive index of the structures increased as the molecular size of probing molecules was decreased. It was possible to obtain an estimate of 1.45 to 1.46 for the refractive index of wall polymers, predominantly peptidoglycans in this case, by extrapolating the curve for refractive index versus molecular radius to a value of 0.2 nm, the approximate radius of a water molecule. This relatively low value for polymer refractive index was interpreted as evidence in favor of the amorphous, elastic model of peptidoglycan structure and against the crystalline, rigid model.
浸没法折射测量和光散射测量被用于测定分离出的细菌细胞壁的平均折射率和物理致密性。将这些结构浸入含有不同浓度且不能穿透细胞壁孔隙的聚合物分子的溶液中，然后估算聚合物浓度或使光散射降至零的聚合物溶液的折射率。由于每种细胞壁制剂都是异质的，因此必须通过外推法估算使光散射为零的介质的折射率。悬浮在牛血清白蛋白溶液中的细胞壁的折射率范围为：结晶节杆菌杆状菌细胞壁的折射率为1.348，而金黄色葡萄球菌52A5磷壁酸缺陷菌株细胞壁的折射率为1.382。这些折射率被用于计算每毫升固体含量的近似值，计算值与根据每克细胞壁干重的葡聚糖不可渗透体积估算的值非常接近。当使用葡聚糖或血清白蛋白等大分子进行浸没法折射测量时，获得的折射率是整个细胞壁的，包括细胞壁聚合物和细胞壁水。当使用能不同程度穿透细胞壁孔隙的较小分子与溶壁微球菌细胞壁一起使用时，随着探测分子的分子尺寸减小，这些结构的平均表观折射率增加。通过将折射率与分子半径的曲线外推到0.2nm（水分子的近似半径）的值，可以估算出细胞壁聚合物（在这种情况下主要是肽聚糖）的折射率为1.45至1.46。聚合物折射率的这个相对较低的值被解释为支持肽聚糖结构的无定形、弹性模型而反对结晶、刚性模型的证据。
