Deamination of adenine results in the formation of hypoxanthine. Xanthine oxidase is needed to oxidize successively hypoxanthine and xanthine to uric acid. It contains hypoxanthine, lumbrofebrin, and lumbritin. Hypoxanthine-guanine phosphoribosyltransferase converts hypoxanthine into IMP in nucleotide salvage. These DHFR-deficient strains require glycine, hypoxanthine, and thymidine for growth. A nitrogenous base called hypoxanthine is assembled directly onto PRPP. Purine nucleoside phosphorylase intraconverts inosine and hypoxanthine. Adenine is deaminated to hypoxanthine, which base pairs to cytosine instead of thymine. The selective culture medium is called HAT medium because it contains hypoxanthine, aminopterin and thymidine. This medium is supplemented with hypoxanthine, aminopterin and thymidine, hence the name HAT medium. PNP metabolizes inosine into hypoxanthine and guanosine into guanine, in each case creating ribose phosphate. Some studies identified another compound, hypoxanthine, present at high extracellular concentration. These chemicals include lactic acid, hypoxanthine, uric acid, ammonia, NADH and formic acid. Hypoxanthine is a naturally occurring purine derivative.