FK was assayed in crude homogenates and the standard reaction mixture contained 25 mM Tris-HCL (pH 8.0), 50 mM KCL, 0.3 mM NAD+ 1 mM ATP, 3 mM MgCl2, 0.5 mM Fru, 1.2 U ml-1 Glc 6-P dehydrogenase (from Leuconostoc mesenteroides) and 0.8 U ml-1 phosphoglucose isomerase.