RELATION BETWEEN THERMAL STABILIZING EFFECT OF SUCROSE ON LDH AND SUCROSE-LDH HYDROGEN-BOND

The thermal stabilizing effect of sugar on freeze-dried protein is stu died, in particular on the relationship between the thermal stabilizin g effect and the degree of sugar-protein hydrogen bond formation. Sucr ose and lactate dehydrogenase (LDH) are used as models for sugar and p rotein. Several freeze-dried samples of LDH involved in sucrose were p repared; they differed in the degree of crystallinity of sucrose, By X -ray diffractometry (XRD) and Fourier transform infrared (FT-IR) spect roscopy, it is found that when sucrose is amorphous in the samples, th e degree of hydrogen bond formation is high and LDH is stabilized rema rkably. In contrast, when sucrose is crystalline, the degree of hydrog en bond formation is low and LDH is inactivated. These results indicat e that the stabilizing effect of sugar is closely related to the sugar -protein hydrogen bond. The influence of sucrose content on the therma l stabilizing effect is also investigated. It is found that there is a n optimum sucrose content for the thermal stabilizing effect. This is because, by the presence of LDH, the amorphous structure of sucrose is stabilized and protected from crystallization that causes loss of suc rose-LDH hydrogen bonds. Thus, we can deduce that sugars and proteins work together to maintain protein activities.