LUNGFISH PROLACTIN EXHIBITS CLOSE TETRAPOD RELATIONSHIPS

This paper describes the isolation and the complete amino-acid sequenc e of prolactin (PRL) from the pituitary glands of African lungfish, Pr otoputerus aethiopicus. We purified the hormone from an alkaline extra ct of the pituitaries using a two-step chromatographic procedure by de tecting specific immunoblot reactivity with rabbit antisera against sa lmon PRL. The lungfish PRL consists of 200 amino-acid residues. Sequen ce comparison revealed that the PRL shows 66% identities with amphibia n, reptilian and bird PRLs, 57% with mammalian PRLs, and 38% with tele ost (modem bony fish) PRLs. Moreover, the PRL contains three disulfide bonds homologous to those of tetrapod PRLs and differs from teleost P RLs which lack the amino-terminal disulfide bond. Thus, the structural features of lungfish PRL indicate a closer relationship to tetrapod P RLs than to teleost PRLs. All PRLs sequenced to date share 22 common a mino acids, which may be important for the activities common to all PR Ls.