Regulatory Peptides 71 (1997) 191–198 Purification and characterization of islet hormones (insulin, glucagon, pancreatic polypeptide and somatostatin) from the Burmese python, Python molurus a, b a c * J. Michael Conlon , Stephen M. Secor , Thomas E. Adrian , Dennis C. Mynarcik , c Jonathan Whittaker a Department of Biomedical Sciences, Creighton University School of Medicine, 2500 California Plaza, Omaha, NE 68178, USA b Department of Physiology, UCLA School of Medicine, Los Angeles, CA 90095, USA c Division of Endocrinology, Department of Medicine, Health Science Centre, S. U.N.Y at Stony Brook, Stony Brook, New York, NY 11794, USA Received 18 May 1997; accepted 21 July 1997 Abstract Insulin was purified from an extract of the pancreas of the Burmese python, Python molurus (Squamata:Serpentes) and its primary 10 20 structure established as: A Chain: Gly-Ile-Val-Glu-Gln-Cys-Cys-Glu-Asn-Thr -Cys-Ser-Leu-Tyr-Glu-Leu-Glu-Asn-Tyr-Cys -Asn. B- 10 20 Chain: Ala-Pro-Asn-Gln-His-Leu-Cys-Gly-Ser-His -Leu-Val-Glu-Ala-Leu-Tyr-Leu-Val-Cys-Gly -Asp-Arg-Gly-Phe-Tyr-Tyr-Ser-Pro- 30 Arg-Ser . With the exception of the conservative substitution Phe → Tyr at position B25, those residues in human insulin that comprise the receptor-binding and those residues involved in dimer and hexamer formation are fully conserved in python insulin. Python insulin 125 was slightly more potent (1.8-fold) than human insulin in inhibiting the binding of [[ I-Tyr-A14] insulin to the soluble full-length recombinant human insulin receptor but was slightly less potent (1.5-fold) than human insulin for inhibiting binding to the secreted 28 extracellular domain of the receptor. The primary structure of python glucagon contains only one amino acid substitution (Ser → Asn) compared with turtle / duck glucagon and python somatostatin is identical to that of mammalian somatostatin-14. In contrast, python 10 20 pancreatic polypeptide (Arg-Ile-Ala-Pro-Val-Phe-Pro-Gly-Lys-Asp -Ala-Ser-Val-Asp-Glu-Leu-Ala-Lys-Phe-Tyr -Thr-Glu-Leu-Gln-Gln- 30 Tyr-Leu-Asn-Ser-Ile -Asn-Arg-Pro-Arg-Phe.NH ) contains only 35 instead of the customary 36 residues and the amino acid sequence 2 of this peptide has been poorly conserved between reptiles and birds (18 substitutions compared with alligator and 20 substitutions compared with chicken).  1997 Elsevier Science B.V. Keywords: Snake; Pancreas; Squamata; Sepentes; Receptor; HPLC 1. Introduction marine lizards) and snakes are sister taxa [2]. The pythons (family Boidea), in contrast to the more advanced snake The snakes are the most rapidly evolving group of families such as Colubridae, Elapidae and Viperidae, retain reptiles and most modern genera belong to families whose many of the primitive features of the earliest snakes, such major radiation has occurred since the beginning of the as vestiges of the pelvic girdle and hind limb [3]. The Miocene [1]. It is generally accepted that snakes evolved reptilian endocrine pancreas has been studied using im- from lizards and the recent identification of the mid- munocytochemical methods and by light and electron Cretaceous fossil Pachyrhachis problematicus as a snake microscopy and cells containing insulin-, glucagon-, with legs suggests that mosasauroids (a group of extinct somatostatin- and avian pancreatic polypeptide (PP)-like immunoreactivities have been identified in the pancreata of * snakes [4,5], alligator [6], crocodile [7] and in several Corresponding author. Tel.: 11 402 2801733; Fax: 11 402 2802690; e-mail: jmconlon@creighton.edu species of lizards [8–10] and turtles [10–12]. 0167-0115 / 97 / $17.00  1997 Elsevier Science B.V. All rights reserved. PII S0167-0115(97)01030-6