Ink S L, Henderson L M
J Biol Chem. 1984 May 10;259(9):5833-7.
Scatchard plot analysis indicated that pyridoxal binds to hemoglobin more than twice as tightly as it does to serum albumin. Comparison of the formation constants for hemoglobin and albumin, using standard competitive binding equations, indicated that the distribution ratio for pyridoxal between erythrocytes and plasma should be 6.5:1. This distribution was approximately the same as that observed when pyridoxal was incubated with whole human blood, suggesting that these two proteins are the primary determinants of the pyridoxal distribution in whole blood. With in situ perfused rat liver the uptake of [3H] pyridoxal from the perfusate was reduced by the inclusion of erythrocytes in the perfusate. This was reflected in the decreased production of 4-pyridoxic acid by the perfused liver from 3.8% to 1.2% of the dose by the addition of erythrocytes to the perfusate. The major labeled metabolites found in the liver were pyridoxal phosphate, pyridoxamine phosphate, and 4-pyridoxic acid for both types of perfusion. In intact animals, reduction of the erythrocytes concentrations to hematocrits of 30-40% increased the recovery in the urine of 3H from administered [3H] pyridoxal from control values of 27-35% to 40-50% of the dose within 48 h. Half of the label in urinary metabolites was in 4-pyridoxic acid.
斯卡查德作图分析表明，吡哆醛与血红蛋白的结合紧密程度是其与血清白蛋白结合紧密程度的两倍多。使用标准竞争结合方程对血红蛋白和白蛋白的形成常数进行比较，结果表明红细胞与血浆中吡哆醛的分布比应为6.5:1。这种分布与将吡哆醛与人全血孵育时观察到的情况大致相同，这表明这两种蛋白质是全血中吡哆醛分布的主要决定因素。在原位灌注大鼠肝脏实验中，向灌注液中加入红细胞会减少[3H]吡哆醛从灌注液中的摄取。这反映在灌注肝脏中4-吡哆酸的生成量从剂量的3.8%降至1.2%，原因是向灌注液中添加了红细胞。两种灌注类型中，在肝脏中发现的主要标记代谢物都是磷酸吡哆醛、磷酸吡哆胺和4-吡哆酸。在完整动物中，将红细胞浓度降低至血细胞比容为30% - 40%，会使给予[3H]吡哆醛后48小时内尿液中3H的回收率从对照值的27% - 35%提高到剂量的40% - 50%。尿液代谢物中一半的标记物存在于4-吡哆酸中。
