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J. Biochem, 2001, Vol. 129, No. 1 147-153
© 2001 Japanese Biochemical Society

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Amphibian Pepsinogens: Purification and Characterization of Xenopus Pepsinogens, and Molecular Cloning of Xenopus and Bullfrog Pepsinogens1

Masayuki Ikuzawa*, Tomofumi Inokuchi{dagger}, Ken-ichiro Kobayashi* and Shigeki Yasumasu*,2

*Life Science Institute, Sophia University Kioi-cho 7-1, Chiyoda-ku, Tokyo 102-8554
{dagger}Department of Biology, Faculty of Education, Utsunomiya University Mine 350 Utsunomiya 321-8505

2To whom correspondence should be addressed. Tel: +81-3-3238-4263, Fax: +81-3-3238-3393, E-mail: s-yasuma{at}hoffman.cc.sophia.ac.jp

Two pepsinogens (Pg C and Pg A) were isolated from the stomach of adult Xenopus laevis by Q-Sepharose, Sephadex G-75, and Mono-Q column chromatographies. Autolytic conversion and activation of the purified Pgs into the pepsins were examined by acid treatment. We determined the amino acid sequences from the NH2-termini of Pg C, pepsin C, Pg A, and pepsin A. Based on the sequences, the cDNAs for Pg C and Pg A were cloned from adult stomach RNA, and the complete amino acid sequences of the Pg C and Pg A were predicted. In addition, a Pg A cDNA was cloned from the stomach of adult bullfrog Rana catesbeiana, and the primary structure of the Pg A was predicted. Molecular phylogenetic analysis showed that such anuran Pg C and Pg A belong to the Pg C group and the Pg A group in vertebrates, respectively. The molecular properties of Pg C and Pg A, such as size, sequences of the activation peptide and active site, profile of autolytic activation, and pH dependency of proteolytic activity of the activated forms, pepsin C and pepsin A, resemble those of Pgs found in other vertebrates. However, the hemoglobin-hydrolyzing activity of Xenopus pepsin C is completely inhibited in the presence of equimolar pepstatin, an inhibitor of aspartic proteinases. Thus, the Xenopus pepsin C differs significantly from other vertebrate pepsins C in its high susceptibility to pepstatin, and closely resembles A-type pepsins.

1The nucleotide sequence data reported in the present paper will appear in the DDBJ/EMBL/GenBank nucleotide sequence databases with accession numbers AB045379 [GenBank] , AB045380 [GenBank] , and AB-045376.


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M. Ikuzawa, S. Yasumasu, T. Inokuchi, K.-i. Kobayashi, K. Nomura, and I. Iuchi
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