Enables ATP binding activity and guanylate kinase activity. Involved in purine nucleotide metabolic process. Located in cytosol and photoreceptor inner segment. Is expressed in several structures, including alimentary system; genitourinary system; integumental system; nervous system; and sensory organ. Orthologous to human GUK1 (guanylate kinase 1). [provided by Alliance of Genome Resources, Apr 2022]