Uses inorganic polyphosphate (polyP) as a donor to convert GDP to GTP and ADP to ATP. Shows a preference for GDP. Can also catalyze the synthesis of polyP from GTP or ATP, but the rate of polyP utilization is 75-fold greater than the rate of polyP synthesis. [phosphate](n) + GTP = [phosphate](n+1) + GDP [phosphate](n) + ATP = [phosphate](n+1) + ADP Mg(2+) is preferred for polyP utilization and Mn(2+) is preferred for polyP synthesis. Homotetramer. Also forms octamers. Belongs to the polyphosphate kinase 2 (PPK2) family. Class I subfamily. Truncated N-terminus.