Catalyzes the phosphorylation of ribose at O-5 in a reaction requiring ATP and magnesium. The resulting D-ribose-5-phosphate can then be used either for sythesis of nucleotides, histidine, and tryptophan, or as a component of the pentose phosphate pathway. ATP + D-ribose = ADP + D-ribose 5-phosphate + H(+) Requires a divalent cation, most likely magnesium in vivo, as an electrophilic catalyst to aid phosphoryl group transfer. It is the chelate of the metal and the nucleotide that is the actual substrate (Probable). Also active with manganase (PubMed:16784868). Activated by a monovalent cation that binds near, but not in, the active site (PubMed:11786021). The most likely occupant of the site in vivo is potassium (PubMed:16784868, PubMed:11786021). Also activated by ammonium ion (PubMed:16784868). Ion binding induces a conformational change that may alter substrate affinity (Probable). Optimum pH is 8-9. Optimum temperature is 30-50 degrees Celsius. Carbohydrate metabolism; D-ribose degradation; D-ribose 5-phosphate from beta-D-ribopyranose: step 2/2. Homodimer. Belongs to the carbohydrate kinase PfkB family. Ribokinase subfamily.