One potential strategy to mitigate the detrimental effects of heat stress on corals is upwelling, which brings deep, cold, nutrient-rich water to the reef surface, creating transient cooling. However, cold temperatures can also stress corals, and it is, therefore, important to understand the mechanisms of both cold and heat stress responses in corals. Similar to how mammals activate thermogenic and adaptive metabolic pathways, corals may also regulate energy and redox metabolism under fluctuating environmental conditions. Guanosine monophosphate reductase (GMPR), a conserved enzyme in purine metabolism, plays a critical role in maintaining intracellular adenine and guanine nucleotide balance. To study this enzyme in corals, we expressed Pocillopora damicornis (PD) GMPR heterologously in Escherichia coli and purified the recombinant protein using nickel–NTA affinity chromatography. SDS-PAGE analysis showed a single band corresponding to the expected molecular weight, indicating high purity. Sequence alignment revealed ~70% identity with mammalian GMPR2 orthologs, suggesting evolutionary conservation of function. Structural modeling and phylogenetic analysis positioned PD GMPR between the GMPR1 and GMPR2 clades, suggesting it may represent an ancestral or functionally intermediate variant. Kinetic analysis determined Km values of 33.76 ± 6.44 μM for GMP and 17.71 ± 0.99 μM for NADPH under fixed substrate concentrations. This study provides the first biochemical characterization of GMPR, which may open the door to uncovering mechanisms of cold tolerance in corals and inform strategies to enhance coral resilience in the face of climate change.