Meta-Biol

• Pathways

Normally in humans, PNP (purine nucleotide phosphorylase) catalyzes the reaction of (deoxy)guanosine with phosphate to yield guanine and (deoxy)ribose. In the absence of PNP activity, however, guanosine and deoxyguanosine accumulate and the formation of deoxy-GTP from the latter is thought to disrupt DNA replication especially in lymphoid cells, leading to severe immunodeficiency. Here, we have annotated the failure of this reaction due to three missense mutant alleles of PNP, identified in patients with severe immunodeficiency and shown to encode catalytically inactive forms of PNP protein (Aust et al. 1992; Williams et al. 1987).