INDUCTION OF δ-AMINOLEVULINIC ACID SYNTHETASE IN CULTURED FRIEND LEUKEMIA CELLS BY DIMETHYL SULFOXIDE AND HUMAN PLACENTAL EXTRACT

δ-Aminolevulinic acid (ALA) synthetase in a culture line of Friend leukemia cells (T-3-Cl-1) was assayed by a newly devised micro-assay method. When the cells were grown in a medium containing dimethyl sulfoxide (Me2SO) or human placental extract (HPE) for 4 days, ALA synthetase activity increased to maximal levels of 4 and 8 times that of control cells. When transferred to a fresh medium without these materials, the ALA synthetase activity of these cells increased 4-fold on the first day, but decreased to the initial level again during subsequent culture for 3 to 4 days. In contrast, when transferred to a medium containing 1.5% Me2SO, the ALA synthetase activity of the cells increased 4-fold on the first day and this level was maintained during the subsequent culture, while when transferred to a medium containing 2.5% HPE, the enzyme activity increased 11-fold on the first day and then decreased gradually to 6 times the initial level during the next 4 days. Heme synthesis also increased in the cells grown in a medium containing 1.5% Me2SO for 3 to 4 days. Differentiation of these leukemia cells in culture is discussed in relation to other phenotypic markers.