Kella N K
Protein Technology Discipline, Central Food Technological Research Institute, Mysore, India.
Int J Biol Macromol. 1989 Apr;11(2):105-12. doi: 10.1016/0141-8130(89)90051-2.
Arachin forms a heat-reversible gel under certain experimental conditions. The minimal gelling concentration for this system is 7.25%. Above minimal gelling concentration calculation of thermodynamic parameters for gelation of arachin revealed a constant delta Hbonding (-1220 cal.mol-1) where delta Sbonding values varied with an increase in protein concentration (ranging from -4.01 e.u. at 7.5% to -3.48 e.u. at 10.0%). The main steps involved in the gelation phenomenon include thermal denaturation of arachin, partial aggregation of heat-denatured protein molecules, setting of protein solution and maturation of the gel formed. Gel maturation process follows first order kinetics and is characterized by a large positive delta G+(+) (22,030 cal.mol-1). Determination of delta H+(+) and delta S+(+) for this process revealed that mostly delta S+(+) (-62.9 e.u.) contributes to the large positive delta G+(+), thus decreasing the overall rate of gel maturation process. This large negative delta S+(+) value probably arises from a loss of entropy of protein molecules because of their increased involvement in gel network formation. The polymer gel network seems to be primarily contributed by a part of both arachin dodecameric and hexameric species.
在某些实验条件下，花生球蛋白会形成热可逆凝胶。该体系的最小凝胶化浓度为7.25%。在最小凝胶化浓度以上，对花生球蛋白凝胶化的热力学参数进行计算，发现其氢键形成焓（ΔHbonding）恒定为-1220 cal·mol-1，而氢键形成熵（ΔSbonding）值随蛋白质浓度的增加而变化（从7.5%时的-4.01 e.u.到10.0%时的-3.48 e.u.）。凝胶化现象涉及的主要步骤包括花生球蛋白的热变性、热变性蛋白质分子的部分聚集、蛋白质溶液的凝固以及形成凝胶的成熟过程。凝胶成熟过程遵循一级动力学，其特征是具有较大的正吉布斯自由能变化（ΔG+(+)为22,030 cal·mol-1）。对该过程的焓变（ΔH+(+)）和熵变（ΔS+(+)）的测定表明，主要是熵变（-62.9 e.u.）导致了较大的正吉布斯自由能变化，从而降低了凝胶成熟过程的总体速率。这种较大的负熵变值可能是由于蛋白质分子参与凝胶网络形成增加导致熵损失所致。聚合物凝胶网络似乎主要由一部分花生球蛋白十二聚体和六聚体构成。
