LORF is an osmoregulatory peptide isolated from the central nervous systems of the leeches Erpobdella octoculata and Theromyzon tessulatum. LORF is also present in the rat brain, coupling to NO release in leech, rat, and human tissues. It is likely that LORF is generated from hemerythrin through cleavage by aspartyl protease.
Although LORF is immunoreactive against oxytocin antiserum, its structure is different from that of oxytocin.LORF is an octapeptide (Ile-Pro-Glu-Pro-Tyr-Val-TrpAsp-OH) identified from two annelids, Erpobdella octoculata and Theromyzon tessulatum. The same peptide was also found in a mammal, Rattus norvegicus. This is an interesting fact, considering the evolutionary distance between annelid and mammal.
LORF has been isolated from the central nervous systems of the leeches Erpobdella octoculata and Theromyzon tessulatum, with both ELISA and dot-blotting assay for oxytocin.An identical peptide has also been isolated from the rat brain.
The precursor-protein mRNA of LORF has yet to be clarified, but the peptide sequence is identical to the N-terminal part of the respiratory pigments myohemerythrin (14 kDa) of the sipunculid Themiste zostericola and hemerythrin of Hirudo medicinalis. It is also highly homologous to those of hemerythrin and a yolk protein, ovohemerythrin (14 kDa), of the leech T. tessulatum.If degradation of those proteins liberates LORF, the processing of the LORF precursor is different from that of other neuropeptides because LORF sequences are not flanked by the dibasic or monobasic cleavage sites. It is likely that an aspartyl protease may play an important role in the synthesis of LORF.
The injection of LORF or LORF-NH2 into the leech provokes an increase in body mass, reflecting an uptake of water; thus, the two peptides exert an antidiuretic effect.The measurement of transepithelial conductance using leech skin suggests that the inhibition of Na+ conductance is involved in the antidiuretic action of LORF.
