Electron transfer protein; may also function as the membrane anchor for the GlpAB dimer. Polyol metabolism; glycerol degradation via glycerol kinase pathway; glycerone phosphate from sn-glycerol 3-phosphate (anaerobic route): step 1/1. Composed of a catalytic GlpA/B dimer and of GlpC. Loosely bound to the cytoplasmic membrane often occurring in vesicles associated with fumarate reductase.