Activity increase after extraction of alkaline phosphatase from human osteoblastic membranes by nonionic detergents: Influence of age and sex

The solubilization of alkaline phosphatase (AP) from osteoblastic eel membr anes obtained from human primary bone cell cultures was studied according t o the age and sex of the donors (17 females, 11 males; age range: 2-77 year s). Cell membranes were treated by non-ionic (n-octyl beta-D-glucopyranosid e, OG), ionic or zwitterionic detergents, then centrifuged. When OG was use d almost all the AP was solubilized. AP activity in supernatant of solubili zation was compared to the activity of the suspension before centrifugation . The activity ratio (AR) increased in function of age for subjects between 65 and 74. Neither total nor specific AP activities were influenced by age or sex. Electrophoresis studies showed that the AP released was a GPI (gly cosyl phosphatidylinositol)-anchored protein, amphipatic form, with 140 kDa as apparent molecular mass. The activity change of AP in the presence of O G may result from age-related modifications either in the AP structure or i n the constituents of the plasma membranes (proteins or phospholipids).