Identification, Preliminary Characterization , and Evidence forRegulation ofInvertase in Streptococcus mutans

Sucrose dissimilation was studied infivestrains ofStreptococcus mutans. Glucose-adapted strain SL-1makesacidmore slowly fromsucrosethanfrom glucose; glucose-adapted strain SL-1gives diauxie growthkinetics inbroth containing limiting amountsof' bothglucose andsucrose.Thus,atleast partof thesucrosedissimilative systemappearsinducible. Sucrase activity was identi- f'ied inthe37,000 x g soluble cell fraction offive strains. Itsintracellular location implies thepresenceofsucrosepermease.Thespecific activity ofthesucraseis higher insucrose-adapted cells thanincells adapted toglucose orother sugars, further suggesting itsinducibility. Theenzyme fromstrain SL-1was partially purified bydiethylaminoethyl-cellulose chromatography andshowntobe a single molecule witha molecular weight ofabout48,000. Thepartially purified enzyme isspecific for sucroseandproduces equimolar glucose andfructose. Since itdegrades raffinose, butnotmelezitose orothera-glucosides, itisan invertase. Theinvertase hasarelatively highKmforitssubstrate anda pHoptimumof5.5 to6.2.Itisactivated byinorganic orthophosphate (P),Pifunctioning as a positive eff'ector. Arsenate can substitute forphosphate. Neither thecrude cell-free extract nor thepartially purified enzyme preparations hasdetectable sucrose phosphorylase activity. A possible potentroleoftheinvertase inthe regulation of' sucrosecarbon flowinS.mutansisdiscussed.