The function of ENSG00000099810 (MTAP, methylthioadenosine phosphorylase) is as follows. Catalyzes the phosphorolytic cleavage of S-methyl-5'- thioadenosine (MTA) to adenine and 5-methylthioribose1-phosphate (PubMed:3091600, PubMed:8687427, PubMed:10404592). Involved in the breakdown of MTA, a major by-product of polyamine biosynthesis (PubMed:3091600, PubMed:8687427, PubMed:10404592). Responsible for the first step in the methionine salvage pathway after MTA has been generated from S-adenosylmethionine (PubMed:3091600, PubMed:8687427, PubMed:10404592). Has broad substrate specificity with 6-aminopurine nucleosides as preferred substrates (PubMed:10404592). {ECO:0000255|HAMAP-Rule:MF_03155, ECO:0000269|PubMed:10404592, ECO:0000269|PubMed:3091600, ECO:0000269|PubMed:8687427}.