title: Prolylhydroxylase activation in IMR 90 fibroblasts: state of differentiation rather than population doubling level determines requirements for enzyme activation.
abstract: The stimulation of prolylhydroxylase activity by ascorbate in IMR 90 fibroblasts grown as monolayer decreases with increasing population doubling level, but the enzyme is not stimulated in IMR 90 fibroblasts of either low or high population doubling level incorporated into collagen lattices in which they cease to divide. The capacity to be activated is restored when cells are released from the lattice. We consider that reduction of stimulation of prolylhydroxylase activity by ascorbate as the population doubling level of cells grown as monolayer increases is not a phenomenon of cell aging. Rather, it is due to an increase in the size of the noncycling subpopulation whose state of differentiation is not the same as that of cells in cycle.
mesh_terms: D002454:Cell Differentiation; D002455:Cell Division; D002470:Cell Survival; D002478:Cells, Cultured; D004789:Enzyme Activation; D005347:Fibroblasts / Q000166:cytology; D006801:Humans; D011393:Procollagen-Proline Dioxygenase / Q000378:metabolism*
chemical_list: D011393:Procollagen-Proline Dioxygenase