Major role in the synthesis of nucleoside triphosphates other than ATP. The ATP gamma phosphate is transferred to the NDP beta phosphate via a ping-pong mechanism, using a phosphorylated active-site intermediate. Shows the highest specificity towards GDP. a 2'-deoxyribonucleoside 5'-diphosphate + ATP = a 2'-deoxyribonucleoside 5'-triphosphate + ADP a ribonucleoside 5'-diphosphate + ATP = a ribonucleoside 5'-triphosphate + ADP Optimum pH is 6.0. Homohexamer. Belongs to the NDK family. There are likely two genes coding for two slightly different proteins, NDK3 and NDK4. The characterization was made on a thylakoid lumen preparation containing probably both proteins.