近生理浓度的脲对核黄素与牛血清蛋白结合作用的影响

Effects of near-physiological concentration of urea on the binding of riboflavin to bovine serum albumin

用CD光谱和荧光光谱研究了近生理浓度的脲存在和不存在两种情况下核黄素和牛血清蛋白之间的相互作用.一定浓度的核黄素结合在牛血清蛋白上可以引起BSA分子结构伸展,二级结构和三级结构减少.近生理浓度的脲可以诱导核黄素变性的牛血清蛋白二级结构和三级结构部分恢复.脲存在时,核黄素对牛血清蛋白的熄灭常数(Kq)以及供体和受体之间的距离(r)增大.相反地,结合常数(Ka)和结合位点数(n)减小.脲存在下,核黄素和牛血清蛋白的结合作用是一个熄灭作用增强,结合作用减弱的过程.人体内血脲的正常范围为0.0025–0.0075M,脲浓度达到0.01 M时,由于核黄素和HAS分子的弱结合作用导致血浆中核黄素缺乏,一些病人可能会因为核黄素缺乏,结合着药物的生物大分子不能被有效地转移进细胞内,不能被某些药物有效地治疗.

The interaction of riboflavin and BSA in the absence and presence of near - physiological concentration of urea was investigated by CD spectra and fluorescence spectroscopy. The conformation of bovine serum albumin extended and the secondary as well as the tertiary structure of it decreased while a certain concentration of riboflavin interacted with the protein. Near - physiological concentration of urea can resume the secondary and the tertiary structure of denatured BSA by riboflavin. Under near - physiological concentration of urea, the quenching constant （Kq） as well as the distance （r） between the donor, BSA and the acceptor, riboflavin increased. On the contrary, binding constant （Ka） and binding sites （n） between them decreased. That is, in the presence of near - physiolog- ical concentration of urea, the quenching effect enhanced and the binding force weakened in riboflavin/BSA sys- tem. The weaker binding ability of HSA, just like BSA, with riboflavin at 0.01 M urea may be one reason that some people fell ill due to the lack of riboflavin in the plasma as blood urea concentrations deviates normal range （0.0025 - 0.0075 M）. Some patients obtained poor treatment by some medicines since the biomolecules bound with these medicines become hard to be transferred into human cells due to the lack of riboflavin.