Intracellular glycerol is usually converted to glycerol-3-phosphate in an ATP-requiring phosphorylation reaction catalysed by glycerol kinase (GlpK) glycerol-3-phosphate activates the antiterminator GlpP [1].

1: Expression of the gene encoding glycerol-3-phosphate dehydrogenase (glpD) in Bacillus subtilis is controlled by antitermination. Holmberg C, Rutberg B; Mol Microbiol 1991;5:2891-2900. PMID:1809833