Regulation and function of sucrose 6-phosphate hydrolase in Streptococcus mutans

Area of Science:

• Microbiology
• Biochemistry
• Enzymology

Background:

• Streptococcus mutans initiates sucrose catabolism via a phosphoenolpyruvate-dependent sucrose phosphotransferase.
• This reaction yields sucrose 6-phosphate, which is subsequently cleaved by sucrose 6-phosphate hydrolase into glucose 6-phosphate and fructose.

Purpose of the Study:

• To investigate the regulatory mechanisms governing sucrose 6-phosphate hydrolase activity in Streptococcus mutans.
• To compare the regulation of sucrose 6-phosphate hydrolase with sucrose phosphotransferase.

Main Methods:

• Enzyme activity assays in permeabilized cells.
• Growth studies using different carbon sources (fructose).
• Analysis of a mutant strain deficient in sucrose 6-phosphate hydrolase.

Main Results:

• Sucrose 6-phosphate hydrolase is constitutively synthesized, while sucrose phosphotransferase activity is inducible.
• Both enzyme activities are repressed when cells are grown on fructose.
• The specific activity of sucrose 6-phosphate hydrolase was measured at approximately 30 mmol/min per mg (dry weight) with an apparent Km of 0.3 mM.
• A mutant lacking sucrose 6-phosphate hydrolase showed reduced sucrose hydrolysis capability.

Conclusions:

• Sucrose catabolism in Streptococcus mutans involves regulated enzymes, with fructose acting as a repressor.
• Sucrose 6-phosphate hydrolase plays a crucial role in sucrose breakdown, as evidenced by the mutant phenotype.