Polyphosphate polymerases make polyphosphate, adding a single phosphate group per catalytic cycle.  Evidence is available to suggest that these enzymes catalyze the transmembrane transport of the growing polyphosphate chain as it is being synthesized.  The channel consists of Vtc1, Vtc3 and Vtc4 in a ratio of 3:1:1 (Guan et al. 2023).