Methylthioadenosine Phosphorylase (MTAP)

Methylthioadenosine phosphorylase (EC 24.2.28) plays a major role in polyamine metabolism and is important for the salvage of both adenine and methionine. For example, as much as 97% of the endogenous adenine produced by human lymphoblasts in culture is formed by catabolism of methylthioadenosine (MeSAdo) by the phosphorylase. MeSAdo, a by-product of the synthesis of the polyamines spermidine and spermine, potently inhibits polyamine aminopropyltransferase reactions if not removed by the above phosphorylase reaction. The encoded enzyme is deficient in many cancers because this gene and the tumor suppressor p16 gene are co-deleted. Multiple alternatively spliced transcript variants have been described for this gene, but their full-length natures remain unknown.