Shibasaki F, Homma Y, Takenawa T
Department of Biosignal Research, Tokyo Metropolitan Institute of Gerontology, Japan.
J Biol Chem. 1991 May 5;266(13):8108-14.
Two types of phosphatidylinositol (PI) 3-kinase (PI3K) have been purified 6250-fold (PI3KI) and 1250-fold (PI3KII) from the cytosol fraction of bovine thymus. Purified PI3KI and PI3KII were found to have apparent molecular masses of 110 and 190 kDa, respectively, by gel filtration. On the other hand, on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, while the molecular mass of PI3KI was again estimated as 110 kDa, PI3KII showed two bands with apparent molecular masses of 110 and 85 kDa, suggesting a heterodimer form. Peptide mapping analysis demonstrated that the 110-kDa protein in PI3KII was the same protein as PI3KI. The specific activity of PI3KI was calculated as 250 nmol/min/mg of protein, while that of PI3KII was 50 nmol/min/mg of protein. The product of PI phosphorylation by PI3KI and PI3KII were confirmed as phosphatidylinositol 3-phosphate by PartiSphere Sax column chromatography. The results show that there are two types of PI 3-kinase in bovine thymus. One exists as a monomer and the other as a heterodimer form. Furthermore, the biochemical properties of these two PI 3-kinases are markedly different. These two types of PI 3-kinase may be regulated differently under physiological conditions.
已从牛胸腺的胞质溶胶部分中纯化出两种磷脂酰肌醇（PI）3-激酶（PI3K），其中一种纯化了6250倍（PI3KI），另一种纯化了1250倍（PI3KII）。通过凝胶过滤发现，纯化后的PI3KI和PI3KII的表观分子量分别为110 kDa和190 kDa。另一方面，在十二烷基硫酸钠-聚丙烯酰胺凝胶电泳中，虽然PI3KI的分子量再次估计为110 kDa，但PI3KII显示出两条带，表观分子量分别为110 kDa和85 kDa，表明其为异二聚体形式。肽图谱分析表明，PI3KII中的110-kDa蛋白与PI3KI是同一种蛋白。PI3KI的比活性计算为250 nmol/（min·mg蛋白），而PI3KII的比活性为50 nmol/（min·mg蛋白）。通过PartiSphere Sax柱色谱法确认，PI3KI和PI3KII催化PI磷酸化的产物均为磷脂酰肌醇3-磷酸。结果表明，牛胸腺中存在两种类型的PI 3-激酶。一种以单体形式存在，另一种以异二聚体形式存在。此外，这两种PI 3-激酶的生化特性明显不同。这两种类型的PI 3-激酶在生理条件下可能受到不同的调节。
