Folate utilization by monomeric versus heterotetrameric sarcosine oxidases

Area of Science:

• Biochemistry
• Enzymology
• Microbial Metabolism

Background:

• Bacterial sarcosine oxidases exist in two forms: heterotetrameric and monomeric.
• These enzymes play a role in sarcosine metabolism, producing formaldehyde.
• Differences in cofactor binding and subunit structure exist between the two forms.

Purpose of the Study:

• To investigate the substrate specificity of bacterial sarcosine oxidases concerning tetrahydrofolates.
• To compare the enzymatic activity and formaldehyde production in the presence of tetrahydrofolates for both enzyme types.
• To elucidate the functional similarities between bacterial and mammalian sarcosine dehydrogenases.

Main Methods:

• Enzyme kinetics assays were performed using purified heterotetrameric and monomeric sarcosine oxidases.
• The effect of [6S]-tetrahydrofolate and [6R,S]-tetrahydropteroyltriglutamate on sarcosine oxidation rates and formaldehyde production was measured.
• Formation of 5,10-methylenetetrahydropteroyltriglutamate was monitored to assess tetrahydrofolate utilization.

Main Results:

• Heterotetrameric sarcosine oxidases showed suppressed formaldehyde formation and increased sarcosine oxidation rates in the presence of [6S]-tetrahydrofolate.
• [6R,S]-tetrahydropteroyltriglutamate was efficiently converted to 5,10-methylenetetrahydropteroyltriglutamate by heterotetrameric enzymes.
• Monomeric sarcosine oxidases exhibited only minor formaldehyde reduction and slow 5,10-methylenetetrahydropteroyltriglutamate formation, attributed to non-enzymatic reactions.

Conclusions:

• Only heterotetrameric bacterial sarcosine oxidases can utilize tetrahydrofolates as substrates.
• This functional capability distinguishes them from monomeric forms and aligns them with mammalian sarcosine and dimethylglycine dehydrogenases.
• The findings highlight a conserved biochemical role for tetrahydrofolate metabolism across different species.