Watanabe J, Asaka Y, Fujimoto S, Kanamura S
Department of Anatomy, Kansai Medical University, Osaka, Japan.
J Histochem Cytochem. 1993 Jan;41(1):43-9. doi: 10.1177/41.1.8417111.
In hepatocytes, NADPH-ferrihemoprotein reductase (reductase) has been hypothesized to exist as aggregates or micelles in endoplasmic reticulum (ER) membrane. However, if the number of reductase molecules per unit area of ER is low, this hypothesis cannot explain how a few reductase molecules efficiently reduce many P-450 molecules. To test this hypothesis, we estimated the numbers of reductase and P-450 molecules per unit ER area (reductase and P-450 densities) by microphotometry of the two enzymes in conjunction with morphometry of ER in periportal, midzonal, and perivenular rat hepatocytes. The reductase density in periportal, midzonal, and perivenular hepatocytes (107-179 molecules/microns 2 of ER) was high enough to efficiently reduce all P-450 molecules in the ER, although the value in perivenular hepatocytes was lowest owing to the relatively greater amount of ER in this region. The pattern of sublobular gradient in the reductase density was similar to that in the P-450 density. Consequently, the molar ratio of P-450 to reductase in ER was similar (about 40:1) in hepatocytes regardless of their positions within the liver lobule.
在肝细胞中，有人提出NADPH-高铁血红素蛋白还原酶（还原酶）在内质网（ER）膜中以聚集体或微团的形式存在。然而，如果每单位面积内质网中还原酶分子的数量很低，这一假设就无法解释少数还原酶分子如何有效地还原众多的P-450分子。为了验证这一假设，我们通过对两种酶进行显微光度测定并结合对大鼠肝小叶周边、中区和中央静脉周围肝细胞内质网的形态测量，估算了每单位内质网面积中还原酶和P-450分子的数量（还原酶和P-450密度）。肝小叶周边、中区和中央静脉周围肝细胞中的还原酶密度（107 - 179个分子/微米²内质网）足以有效地还原内质网中的所有P-450分子，尽管中央静脉周围肝细胞中的还原酶密度值最低，因为该区域内质网的量相对较多。还原酶密度的小叶下梯度模式与P-450密度的模式相似。因此，无论肝细胞在肝小叶内的位置如何，内质网中P-450与还原酶的摩尔比相似（约为40:1）。
