Catalyzes the conversion of AMP and phosphate to adenine and ribose 1,5-bisphosphate (R15P). Exhibits phosphorylase activity toward CMP, dCMP and UMP in addition to AMP. Functions in an archaeal AMP degradation pathway, together with R15P isomerase and RubisCO. AMP + phosphate = adenine + alpha-D-ribose 1,5-bisphosphate CMP + phosphate = alpha-D-ribose 1,5-bisphosphate + cytosine phosphate + UMP = alpha-D-ribose 1,5-bisphosphate + uracil AMP phosphorolysis is allosterically regulated by the substrate AMP. kcat is 39.1 sec(-1), 15.0 sec(-1), 10.5 sec(-1) and 2.7 sec(-1), with CMP, AMP, UMP, and GMP as substrate, respectively (at 85 degrees Celsius). KM for AMP was not determined because the reaction does not follow Michaelis-Menten kinetics. Forms an exceptionally large macromolecular structure (>40-mers) in solution. Constitutively expressed (at protein level). Does not respond to the addition of nucleosides. The N-terminal domain (residues 1-84), characteristic of archaeal AMPpases, is essential for enzymatic activity, participating in multimerization as well as domain closure of the active site upon substrate binding. Harbors two dimer interfaces within a single molecule: one by the central domain and the other by the C-terminal domain; these two interactions can continuously occur in a repetitive manner, leading to multimerization. Belongs to the thymidine/pyrimidine-nucleoside phosphorylase family. Type 2 subfamily.