Park J W, Chakrabarti B
Biochim Biophys Acta. 1978 Dec 18;544(3):667-75. doi: 10.1016/0304-4165(78)90341-0.
Circular dichroism studies of glycosaminoglycans including chemically transformed heparins at various pH values reveal that carboxyl chromophore plays an important role in the dichroic behavior of the polymers. With decreasing pH, iduronic acid-containing glycosaminoglycans show increased negative ellipticity near 220 nm whereas the polymers containing glucuronic acid display enhanced negative dichroism near 230 nm and decreased negative dichroism around 210 nm. The pH-dependent optical properties have been utilized to determine the pKa values of uronic acid moieties. The acid strengths of the iduronic acid-containing glycosaminoglycans are inherently smaller than those of corresponding glucuronic acid-containing polymers. Glycosaminoglycans in which the amino sugars are linked with iduronic acid display a very weak n leads to pi* amide transition, or none. The rotational strength at 210 nm of these polymers is largely due to iduronic acid moieties. The CD variations above 200 nm with change in pH do not indicate any major conformational transition of the molecules but the difference between dermatan sulfate and heparin can be attributed to difference either in iduronic acid conformation or in intersaccharide linkages.
对包括化学转化肝素在内的糖胺聚糖在不同pH值下的圆二色性研究表明，羧基发色团在聚合物的二色性行为中起重要作用。随着pH值降低，含艾杜糖醛酸的糖胺聚糖在220nm附近显示出增加的负椭圆率，而含葡萄糖醛酸的聚合物在230nm附近显示出增强的负二色性，在210nm附近负二色性降低。pH依赖性光学性质已被用于确定糖醛酸部分的pKa值。含艾杜糖醛酸的糖胺聚糖的酸强度本质上小于相应的含葡萄糖醛酸的聚合物。氨基糖与艾杜糖醛酸相连的糖胺聚糖显示出非常弱的n→π*酰胺跃迁，或者没有跃迁。这些聚合物在210nm处的旋转强度主要归因于艾杜糖醛酸部分。pH变化时200nm以上的圆二色性变化并不表明分子有任何主要的构象转变，但硫酸皮肤素和肝素之间的差异可归因于艾杜糖醛酸构象或糖间连接的差异。
