Involved in maintaining the homeostasis of cellular nucleotides by catalyzing the interconversion of nucleoside phosphates. Has GTP:AMP phosphotransferase and ITP:AMP phosphotransferase activities. Does not accept ATP as phosphate donor. a ribonucleoside 5'-triphosphate + AMP = a ribonucleoside 5'-diphosphate + ADP Optimum temperature is 30 degrees Celsius. Active at 30 degrees Celsius, and rapidly inactivated with an increase of 5 degrees Celsius. Monomer. Expression level is low on glucose or other fermentable carbon sources. Induced about 3-fold on glycerol, and significantly induced by ethanol. Consists of three domains, a large central CORE domain and two small peripheral domains, NMPbind and LID, which undergo movements during catalysis. The LID domain closes over the site of phosphoryl transfer upon GTP binding. Assembling and dissambling the active center during each catalytic cycle provides an effective means to prevent GTP hydrolysis. Present with 704 molecules/cell in log phase SD medium. Depending on the yeast strain, the GTP:AMP phosphotransferase is encoded by ADK2 with or without a single base pair deletion/insertion near the 3' end of the open reading frame, resulting in a long or a short form. The ADK2 short form (this entry) is also referred to as PAK3, while the long form has been named AKY3. A sequence of the long form can be found in strain D273-10B (AC E9P974). The modified C-terminus in the long form contributes to protein folding and is critical for protein stability. Belongs to the adenylate kinase family. AK3 subfamily.