Bacterial glycerol uptake and catabolism through glycerol 3-phosphate

Aerobic glycerol utilisation in bacteria by the phosphorylating route, from channel-mediated uptake to dihydroxyacetone phosphate. A GlpF aquaglyceroporin lets glycerol diffuse across the cytoplasmic membrane down its concentration gradient. The ATP-dependent glycerol kinase GlpK traps it in the cell as sn-glycerol 3-phosphate. The FAD-dependent glycerol-3-phosphate:quinone dehydrogenase GlpD then oxidizes that intermediate to dihydroxyacetone phosphate on the cytoplasmic face of the plasma membrane, passing the electrons to the respiratory quinone pool. The same GlpF-GlpK-GlpD route is used by Escherichia coli and Pseudomonas putida and is encoded by the glp genes of many other bacteria.

The module starts with extracellular glycerol and ends with dihydroxyacetone phosphate plus reduced quinone. Passive channel transport does not itself consume ATP; phosphorylation by GlpK provides metabolic trapping. Alternative active glycerol transporters, glycerol dehydrogenase routes, phospholipid-derived glycerol 3-phosphate, quinol reoxidation, and downstream glycolysis are outside the boundary. Regulation (GlpR repression, catabolite control, and inducer exclusion of GlpK by EIIA-Glc and fructose 1,6-bisphosphate) is supporting context, not a required part. Scope is kept bacterial, with E. coli K-12 and P. putida KT2440 as the experimental and pathway exemplars. Eukaryotes have the same two catalytic activities but a different arrangement: in yeast, GUT2 acts at the mitochondrial inner membrane and uptake is largely by an H+ symporter. That route is modelled in glycerol_metabolism. The PANTHER subfamilies are named after eukaryotic members (PTHR43829:SF9 AQUAPORIN-9; PTHR11985:SF15 GLYCEROL-3-PHOSPHATE DEHYDROGENASE, MITOCHONDRIAL), but both bacterial exemplars are classified in them. The anaerobic GlpABC dehydrogenase (PTHR11985:SF35) is an alternative third step under anaerobic conditions. It is not modelled here.