FIG. 4.

Differential effect of heparin on stimulation of DNA synthesis in NIH 3T3 cells by some FGF4 mutants. Thymidine uptake in NIH 3T3 cells in response to increasing concentrations of wild-type FGF4 and FGF4 mutants in the presence and absence of exogenous heparin was determined as described in Materials and Methods. (A) A representative experiment with the E159A and L203A mutants. (B) A representative experiment with the K183A/K188A and N89A/K198A double mutants. These results and those obtained with other mutants are summarized in Table 2, where we calculate the 50% effective dose—the concentration of mutant necessary to achieve 50% of maximum DNA synthesis produced by the wild-type FGF4.