Nucleoside kinase with broad substrate specificity. Catalyzes the phosphorylation of a variety of nucleosides to the corresponding nucleoside 5'-mono-phosphate in the presence of phosphate donors and divalent cations. Displays the most efficient activity with guanosine, followed by inosine, cytidine, and adenosine. Negligible enzymatic activity is detected with thymidine, uridine, and 2-deoxyadenosine. ATP is the most efficient phosphate donor, but can also use GTP and ITP. Shows no sugar kinase activity, since it is unable to phosphorylate ribose, fructose-1-phosphate, or fructose-6-phosphate. adenosine + ATP = ADP + AMP + H(+) ATP + cytidine = ADP + CMP + H(+) ATP + guanosine = ADP + GMP + H(+) ATP + inosine = ADP + H(+) + IMP Can use Mg(2+) and Co(2+) with equal efficiency in vitro, and to a lesser extent, Mn(2+), but not Ni(2+). kcat is 0.072 sec(-1) with ATP and guanosine as substrates. kcat is 0.16 sec(-1) with ATP and inosine as substrates. kcat is 0.064 sec(-1) with ATP and cytidine as substrates. kcat is 0.084 sec(-1) with ATP and adenosine as substrates. kcat is 0.27 sec(-1) with GTP and inosine as substrates (at pH 8.0 and 22 degrees Celsius). Optimum pH is 6.6. Significant activity is observed over the pH range of 6.4 to 7.8. Enzymatic activity decreases markedly at pH 8.0 and at pH 6.2 and below. Homodimer. Belongs to the carbohydrate kinase PfkB family.