Table 1.

Specific enzymatic activities of the mutant fMFR cell homogenate, soluble fraction and membranes as determined by monitoring the reduction of fumarate by benzylviologen radicals.

	Specific activities (U mg−1)
Wild-type cell homogenate (QFR)	1.45
ΔfrdCAB cell homogenate	< 0.01
Mutant fMFR cell homogenate	0.48
Mutant fMFR soluble fraction	0.20
Mutant fMFR membranes	0.14

As positive and negative control cell homogenate activities of the wild type and the ΔfrdCAB mutant are shown respectively. One unit (U) of activity is defined as the consumption of 1 μmol fumarate per minute at 37°C.