Manthey C L, Sladek N E
Department of Pharmacology, University of Minnesota, Minneapolis 55455.
Biochem Pharmacol. 1988 Jul 15;37(14):2781-90. doi: 10.1016/0006-2952(88)90041-x.
A spectrophotometric assay was developed and utilized to directly characterize aldehyde dehydrogenase-catalyzed oxidation of aldophosphamide to carboxyphosphamide by soluble and solubilized particulate fractions prepared from mouse liver homogenates. Vmax values of 3310 and 1170 nmol/min/g liver were obtained for the soluble and solubilized particulate fractions respectively. Km values were 22 and 84 microM respectively. Alkaline pH optimums were observed in each case. Aldehyde dehydrogenase-catalyzed oxidation of aldophosphamide by the soluble fraction was markedly more temperature responsive. Catalysis of aldophosphamide and acetaldehyde or benzaldehyde oxidation was apparently by the same isozyme(s) in the soluble fraction. Similarly, low Km (acetaldehyde/benzaldehyde) and high Km (acetaldehyde/benzaldehyde) isozymes each apparently catalyzed the oxidation of aldophosphamide in the solubilized particulate fraction. Our findings suggest that (1) oxidation of aldophosphamide to carboxyphosphamide by mouse liver is catalyzed largely by the predominant aldehyde dehydrogenase isozyme present in the soluble fraction (cytosol) of this tissue, and (2) isozymes that catalyze aldophosphamide oxidation are not different from those that catalyze the oxidation of acetaldehyde and benzaldehyde, though the relative contribution of each isozyme within the solubilized particulate fraction to the catalysis of aldophosphamide oxidation remains to be determined.
开发并利用了一种分光光度测定法，以直接表征由小鼠肝脏匀浆制备的可溶性和可溶解颗粒部分中醛脱氢酶催化醛磷酰胺氧化为羧基磷酰胺的过程。可溶性部分和可溶解颗粒部分的Vmax值分别为3310和1170 nmol/分钟/克肝脏。Km值分别为22和84 microM。在每种情况下均观察到碱性pH最适值。可溶性部分中醛脱氢酶催化的醛磷酰胺氧化对温度的响应明显更大。可溶性部分中醛磷酰胺与乙醛或苯甲醛氧化的催化作用显然是由相同的同工酶进行的。同样，低Km（乙醛/苯甲醛）和高Km（乙醛/苯甲醛）同工酶显然各自催化了可溶解颗粒部分中醛磷酰胺的氧化。我们的研究结果表明：（1）小鼠肝脏中醛磷酰胺氧化为羧基磷酰胺的过程主要由该组织可溶性部分（细胞质）中存在的主要醛脱氢酶同工酶催化；（2）催化醛磷酰胺氧化的同工酶与催化乙醛和苯甲醛氧化的同工酶没有差异，尽管可溶解颗粒部分中每种同工酶对醛磷酰胺氧化催化的相对贡献仍有待确定。
