Nicotinate hydroxylase, part of the hnx cluster involved in the purine degradation. The nicotinate hydroxylase hnxS accepts nicotinate as a substrate and catalyzes the first step of nicotinate catabolism. HnxS accepts also hypoxanthine, but not xanthine, as a substrate. The major facilitator-type transporters hxnP and hxnZ are probably involved in the uptake of nicotinate-derived metabolites, and the oxidoreductases hxnT and hxnY in the further metabolism of 6-OH nicotinic acid