Standeven A M, Wetterhahn K E
Department of Pharmacology and Toxicology, Dartmouth Medical School, Hanover, NH.
Carcinogenesis. 1991 Sep;12(9):1733-7. doi: 10.1093/carcin/12.9.1733.
Chromium (VI) reductase activity was measured in ultrafiltrates of rat liver and kidney after various pretreatments in vitro at 37 degrees C and pH 7.0. Preincubation of ultrafiltrates with L-ascorbate oxidase (EC 1.10.3.3), which specifically eliminated ascorbate, blocked approximately 80% of the Cr(VI) reductase activity. Heat-denatured ascorbate oxidase had no effect on Cr(VI) reductase activity in ultrafiltrates. Preincubation of ultrafiltrates with N-ethylmaleimide, which non-specifically blocked sulfhydryls, including reduced glutathione, decreased Cr(VI) reductase activity by only 20%. Treatment of male Sprague-Dawley rats with phorone decreased non-protein sulfhydryl (NPSH) levels in rat liver by greater than 90% and tripled reduced ascorbate levels 2 h after treatment. Ultrafiltrates of liver prepared from phorone-treated rats had twice the Cr(VI) reductase activity of control ultrafiltrates, and greater than 95% of this activity could be blocked by preincubation with ascorbate oxidase. Treatment of rats with sodium dichromate (20 mg/kg) caused a significant decrease in ascorbate levels in kidney but not liver, and no change in NPSH levels in kidney or liver, 15 min after treatment. We conclude that ascorbate is the major reductant of Cr(VI) in rat liver and kidney ultrafiltrates and may well be the major non-enzymatic reductant of Cr(VI) in rat liver and kidney in vivo.
在37摄氏度和pH 7.0条件下对大鼠肝脏和肾脏的超滤液进行各种体外预处理后，测定了其中铬（VI）还原酶的活性。超滤液与特异性消除抗坏血酸的L-抗坏血酸氧化酶（EC 1.10.3.3）预孵育，可阻断约80%的Cr（VI）还原酶活性。热变性的抗坏血酸氧化酶对超滤液中的Cr（VI）还原酶活性没有影响。超滤液与N-乙基马来酰亚胺预孵育，N-乙基马来酰亚胺非特异性地阻断包括还原型谷胱甘肽在内的巯基，使Cr（VI）还原酶活性仅降低20%。用佛尔酮处理雄性Sprague-Dawley大鼠，2小时后大鼠肝脏中的非蛋白巯基（NPSH）水平降低超过90%，还原型抗坏血酸水平增加两倍。用佛尔酮处理的大鼠肝脏制备的超滤液的Cr（VI）还原酶活性是对照超滤液的两倍，且该活性的95%以上可通过与抗坏血酸氧化酶预孵育而被阻断。用重铬酸钠（20 mg/kg）处理大鼠15分钟后，肾脏中的抗坏血酸水平显著降低，但肝脏中的抗坏血酸水平未降低，肾脏和肝脏中的NPSH水平也没有变化。我们得出结论，抗坏血酸是大鼠肝脏和肾脏超滤液中Cr（VI）的主要还原剂，很可能也是大鼠肝脏和肾脏体内Cr（VI）的主要非酶还原剂。
