Proteins immunoreactive with antibody against a human leptin fragment are found in serum and tissues of the sea lamprey, Petromyzon marinus L

An affinity-purified, polyclonal antibody raised against a peptide correspo nding to amino acids 137-156 at the carboxy terminus of human leptin (16 kD ) was used to search for immunoreactive protein(s) in the lamprey, Petromyz on marinus. Immunoblots of serum from different phases of the life cycle sh owed the presence of a 65-kD immunoreactive protein in the larvae and all s tages of metamorphosis but not in feeding juvenile and upstream migrant adu lts. Extracts of tissues known to store fat were also examined using the sa me antibody. Muscle and fat column from all phases tested (larvae, stage 2 and 4 metamorphosing animals, feeding juveniles and upstream migrants) show ed 100- and 50-kD immunoreactive proteins. Extracts of nephric fold, the pr imary site of fat storage during metamorphosis, lacked the 100-kD protein b ut had the 50 kD; they also had a 16 kD immunoreactive protein not found in the other tissues. The immunoreactivity of the proteins of both serum and tissue extracts was blocked by pretreatment of the antibody with the leptin -derived antigen. The results indicate that P. marinus has proteins that sh are at least one epitope with mammalian leptin. (C) 2001 Elsevier Science I nc. All rights reserved.