Holmgren P A, Stigbrand T, Beckman G
Biochem Genet. 1977 Jun;15(5-6):521-30. doi: 10.1007/BF00520195.
The I variant of placental alkaline phosphatase was purified to homogeneity by means of DEAE-cellulose chromatography, isoelectric focusing, and gel filtration on AcA-34. The specific activity of the I variant was found to be 3.33 micronkat/mg. The enzyme is a dimer with an isoelectric point of 4.6 and a molecular weight of 120,000 as determined by sodium dodecylsulfate electrophoresis. The amino acid composition and other physiocochemical properties of the I variant were compared with those of the more common F and S variants. The low activity associated with the I variant is apparently not due to a low specific activity, but to decreased molecular stability. The behavior in the ultracentrifuge and other observations suggest that the I variant differs from the F and S variants in surface charge distribution.
通过DEAE - 纤维素色谱法、等电聚焦以及在AcA - 34上的凝胶过滤，将胎盘碱性磷酸酶的I变体纯化至同质。发现I变体的比活性为3.33微卡特/毫克。该酶是一种二聚体，通过十二烷基硫酸钠电泳测定其等电点为4.6，分子量为120,000。将I变体的氨基酸组成和其他物理化学性质与更常见的F和S变体进行了比较。与I变体相关的低活性显然不是由于比活性低，而是由于分子稳定性降低。超速离心行为和其他观察结果表明，I变体在表面电荷分布上与F和S变体不同。
