May function as an output molecule from the suprachiasmatic nucleus (SCN) that transmits behavioral circadian rhythm. May also function locally within the SCN to synchronize output. Potently contracts gastrointestinal (GI) smooth muscle. Expressed in the testis and, at low levels, in the small intestine. Activated by CLOCK and BMAL1 heterodimers and light; inhibited by period genes (PER1, PER2 and PER3) and cryptochrome genes (CRY1 and CRY2). The disease is caused by variants affecting distinct genetic loci, including the gene represented in this entry. The genetics of hypogonadotropic hypogonadism involves various modes of transmission. Oligogenic inheritance has been reported in some patients carrying mutations in PROK2 as well as in other HH-associated genes including PROKR2 (PubMed:23643382). Belongs to the AVIT (prokineticin) family.