Stankovich M T, Massey V
Biochim Biophys Acta. 1976 Dec 8;452(2):335-44. doi: 10.1016/0005-2744(76)90183-2.
The redox potential of deazariboflavin has been determined for pH values from 5.5 to 9.2 by equilibration with riboflavin and lumiflavin 3-acetate. The position of the equilibrium with riboflavin was measured spectrophotometrically and fluorimetrically; the equilibrium potential with lumiflavin 3-acetate was measured spectrophotometrically and potentiometrically. The Em7 for deazariboflavin was found to be--0.273 +/- 0.003 V against the standard hydrogen electrode. Equilibrium with flavodoxin at pH 9.5 and 10.0 was also used to determine the redox potential of deazariboflavin at high pH values. The pK of dihydrodeazariboflavin was found from the break in the potential vs. pH diagram and from spectrophotometric pH titration. The pK value obtained by both methods is 7.00 +/- 0.05. We found that borate, a product of the reducing agent borohydride, complexed with the ribityl sidechain of deazariboflavin, causing a shift in the pK for the reduced form to values of about 8.
通过与核黄素和3-乙酸基黄素单核苷酸平衡，测定了脱氮核黄素在pH值5.5至9.2范围内的氧化还原电位。与核黄素平衡的位置通过分光光度法和荧光法测量；与3-乙酸基黄素单核苷酸平衡的电位通过分光光度法和电位分析法测量。发现脱氮核黄素相对于标准氢电极的Em7为-0.273±0.003V。在pH 9.5和10.0条件下与黄素氧还蛋白平衡，也用于测定高pH值下脱氮核黄素的氧化还原电位。通过电位对pH图中的转折点和分光光度pH滴定法确定二氢脱氮核黄素的pK值。两种方法得到的pK值均为7.00±0.05。我们发现，还原剂硼氢化钠的产物硼酸盐与脱氮核黄素的核糖醇侧链络合，导致还原形式的pK值向约8的值偏移。
