AMINO-ACID-SEQUENCE DIVERSITY OF PANCREATIC-POLYPEPTIDE AMONG THE AMPHIBIA

It has been suggested that the amino acid sequence of pancreatic polyp eptide (PP) may provide a useful molecular marker with which to study evolutionary relationships between tetrapods but few PP sequences from amphibia are available to test this hypothesis. PPs have been purifie d from the pancreata of five species belonging to the different orders of amphibians. Their amino acid sequences were established as: APSEPE HPGD(10) NASPDELAKY(20) YSDLWQYITF(30) VGRPRY for the lesser siren, Si ren intermedia (Caudata); GPTEPIHPGK(10) DATTPEELTKY(20) YSDLYDYITL30 VGRSRW for the caecilian, Typhlonectes natans (Gymnophiona); and TPSEP QHPGD(10) QASPEQLAQY(20) YSDLWQYITF(30) VTRPRF for the cane toad, Bufo marinus (Anura). The structure of Rana sylvatica PP is the same as th at of Rana catesbeiana PP whereas PP from the green frog Rana ridibund a contains one substitution (His(6) --> Gln). The data provide further support for the conclusion that the amino acid sequence of Pr has bee n poorly conserved during evolution with only 17 residues invariant am ong the eight species of amphibia yet studied and only 8 residues (pro (5), Pro(8) Gly(9), Ala(12), Leu(2+), Tyr(27), Arg(33), and Arg(35)) i nvariant among all tetrapods. A maximum parsimony analysis based upon the amino acid sequence of PP and using the sequence of frog PYY as ou tgroup to polarize the in-group taxa generates a consensus phylogeneti c tree in which the Amniota and Amphibia form two distinct clades. How ever, such a tree does not permit valid conclusions to be drawn regard ing branching order within the Amphibia. (C) 1998 Academic Press.