TABLE 1.

Activation by FBP of the insertion mutants in the direction of ADP-Glc synthesis and pyrophosphorolysis

EnzymeaFBP activation of insertion mutant in the direction ofb:
ADP-Glc synthesisPyrophosphorolysis
A0.5 (mM)nActivation (fold)Vmax (U/mg)A0.5 (mM)nActivation (fold)Vmax (U/mg)
Wild type0.0651.85010.10.0251.79.918.7
Ins30.951.5>200c0.110.6501.9>100c0.10
Ins8N/AdN/AN/A0.43eN/AN/AN/A1.29e
Ins220.431.2355.810.2701.5129.20
Ins270.251.8606.440.0601.8156.03
Ins651.101.9>2000.200.9301.7>1000.15
Ins680.312.3>2000.630.2101.8>1000.30
Ins780.771.91500.230.3301.6400.26
Ins1040.301.4454.320.0811.9187.45
Ins1190.511.7>2004.100.2502.12510.80
Ins1260.811.71350.430.3301.7370.54
  • a Enzymes were partially purified and assayed as indicated in Materials and Methods.

  • b Deviations of the four parameters, A0.5, n, activation (fold), and Vmax, were lower than 15%. A0.5 is the amount of activator needed to obtain 50% of the maximal activation. Vmax is the maximum activity. The Hill coefficient is n. Activation (fold) is the ratio between the activities in the presence and absence of saturated concentrations of FBP as defined in Materials and Methods.

  • c These values (>200 and >100) indicate that the enzymes showed very low activity in the absence of FBP.

  • d N/A, not applicable (activation by FBP was negligible, and constants could not be determined).

  • e Activity in the presence of 2.5 mM FBP was not significantly different from activity in the absence of activator.