Catalyzes the phosphorylation of the dietary vitamin B6 vitamers pyridoxal (PL), pyridoxine (PN) and pyridoxamine (PM) to form pyridoxal 5'-phosphate (PLP), pyridoxine 5'-phosphate (PNP) and pyridoxamine 5'-phosphate (PMP), respectively (PubMed:17707212, Ref.3, PubMed:22079857) (By similarity). PLP is the active form of vitamin B6, and acts as a cofactor for over 140 different enzymatic reactions (Probable). ATP + pyridoxal = ADP + H(+) + pyridoxal 5'-phosphate ATP + pyridoxamine = ADP + H(+) + pyridoxamine 5'-phosphate ATP + pyridoxine = ADP + H(+) + pyridoxine 5'-phosphate Divalent metal cations. Zn(2+) is the most effective cation for catalysis. Activity is stimulated by Mg(2+). Activated by K(+) in the presence of triethanolamine (pH 7.3). kcat is 1.23 sec(-1) for ATP. kcat is 1.35 sec(-1) for PL. Optimum pH is 5.5-6.0. Activity decreases slowly above pH 6.0, to approximately 35% of the maximum at pH 8.5. Inactive below pH 4.5. Optimum temperature is 50 degrees Celsius. Stable below 40 degrees Celsius. Cofactor metabolism; pyridoxal 5'-phosphate salvage; pyridoxal 5'-phosphate from pyridoxal: step 1/1. Cofactor metabolism; pyridoxal 5'-phosphate salvage; pyridoxamine 5'-phosphate from pyridoxamine: step 1/1. Cofactor metabolism; pyridoxal 5'-phosphate salvage; pyridoxine 5'-phosphate from pyridoxine: step 1/1. Homodimer. Expressed in silk gland and fat body of the larva. Expressed in fifth instar larva (PubMed:26780217, PubMed:27106120). In the silk gland, highest level on the first day of 5th instar larva, then displaying a decreasing trend daily. In the fat body, expression level is high in the early and late stages, and low in the middle stage of 5th instar larva (PubMed:26780217). Expression is up-regulated by exogenous molting hormone (beta-ecdysterone) and down-regulated by exogenous juvenile hormone (JH) III in the silk gland and fat body of the fifth instar larva. RNAi-mediated knockdown of this protein causes significant decrease in transcription levels of pyridoxal 5'-phosphate (PLP)-dependent enzymes phosphoserine aminotransferase (PSAT) and aspartate aminotransferase (glutamic-oxaloacetic transaminase) in silk gland, fat body and midgut of the fifth instar larva. Belongs to the pyridoxine kinase family.