Sulfoglycolysis

Sulfoglycolysis is a catabolic process in primary metabolism in which sulfoquinovose (6-deoxy-6-sulfonato-glucose) is metabolized to produce energy and carbon-building blocks . Sulfoglycolysis pathways occur in a wide variety of organisms, and enable key steps in the degradation of the plant/cycanobacterial sulfolipid sulfoquinovosyl diacylglycerol (SQDG) into sulfate. Sulfoglycolysis converts sulfoquinovose (C₆H₁₂O₈S⁻) into pyruvate CH₃COCOO⁻ + H⁺. The free energy is used to form the high-energy molecules ATP (adenosine triphosphate) and NADH (reduced nicotinamide adenine dinucleotide). Unlike glycolysis, all known sulfoglycolysis pathways convert only half the carbon content of sulfoquinovose into pyruvate; the remained is excreted as a C₃-sulfonate: 2,3-dihydroxypropanesulfonate (DHPS) or sulfolactate (SL). Two sulfoglycolytic processes have been discovered. The sulfoglycolytic Embden-Meyerhof-Parnas (sulfo-EMP) pathway involves the degradation of sulfoquinovose to 2,3-dihydroxypropanesulfonate (DHPS) , and shares similarity with the Embden-Meyerhof-Parnas glycolysis pathway. The sulfoglycolytic Entner-Doudoroff (sulfo-ED) pathway involves the degradation of sulfoquinovose to sulfolactate , and shares similarity to the Entner-Doudoroff pathway of glycolysis. Both pathways lead to the production of dihydroxyacetone phosphate in processes that consume ATP. Energy is formed in later stages through the 'pay-off' phase of glycolysis through substrate-level phosphorylation to produce ATP and NADH.

Production of sulfoquinovose

Sulfoquinovose is obtained from SQDG by the action of sulfoquinovosidases, which are glycoside hydrolases that can hydrolyse the glycosidic linkage in SQDG, or its deacylated form, sulfoquinovosyl glycerol .

Sulfo-EMP pathway

The major steps in the sulfo-EMP pathway are:

• isomerization of sulfoquinovose to sulfofructose;
• phosphorylation of sulfofructose to sulfofructose-1-phosphate;
• retro-aldol cleavage of sulfofructose-1-phosphate to afford dihydroxyacetone phosphate and (S)-sulfolactaldehyde;
• reduction of sulfolactaldehyde to (S)-2,3-dihydroxypropane-1-sulfonate.

Sulfo-ED pathway

The major steps in the sulfo-ED pathway are:

• oxidation of sulfoquinovose to sulfogluconolactone;
• hydrolysis of sulfogluconolactone to sulfogluconate acid;
• dehydration of sulfogluconic acid to 2-keto-3,6-dideoxy-6-sulfogluconate;
• retro-aldol cleavage of 2-keto-3,6-dideoxy-6-sulfogluconate to give pyruvate and (S)-sulfolactaldehyde;
• oxidation of sulfolactaldehyde to (S)-sulfolactate.