The initial step of disaccharide dissimilation by Actinomyces viscosus serotype 2 strain M-100 was studied. Sucrase activity was found in the 3,000 x g particulate fraction and the 37,000 x g soluble fraction of the cells, whereas lactase activity was found almost exclusively in the 37,000 x g soluble fraction. Neither sucrase nor lactase activity was appreciable in the culture liquor. Sucrose phosphorylase, a-glucosidase, and polysaccharide synthesis activities were not observed in the soluble cell fraction. The sucrase was identified as

The regulation of diethylaminoethyl-partially purified invertase (EC 3.2.1.26; ,8-D-fructofuranoside fructohydrolase) from the 37,000 x g-soluble intracellular fluid of Actinomyces viscosus serotype 2 strain M-100 was studied. Glycolytic intermediates, mono-, di-, and triphosphate nucleotides, inorganic phosphate, and various divalent cations were tested for regulatory effects. Fructose-6-phosphate (F6P) and fructose-1,6-diphosphate (FDP) were found to act as noncompetitive inhibitors of invertase. The Ki values for F6P and FDP were found to be 3.4 and 5.1 mM, respectively. The Hill coefficient for sucrose was 1.03 and remained unchanged in the presence of varying amounts of F6P or FDP.