This paper describes the identification andcharacterization of a novel cDNA encoding a putativeprotein of 254 amino acids that is highly homologous totriosephosphate isomerase. The cDNA was isolated by subtractive hybridization and wasdifferentially expressed in the remnant rat ileum aftermassive small bowel resection. The novel triosephosphateisomerase was named rsTPI (resection-induced TPI) and the putative protein encoded RSTPI. Thenucleotide and amino acid sequences of rsTPI and RSTPIwere about 60% and 62% homologous to Giardia lamblia TPIand TPI, respectively. Active catalytic sites (Lys 13, His 95, and Glu 167) and the peptidemotifs, AYEPVWSIGT and GGASLKPEF found in othertriosephosphate isomerases were conserved in RSTPI.rsTPI expression was detected in normal ileum andpancreas by reverse transcription-polymerase chainreaction. Expression of rsTPI in remnant rat ileum wasdetectable by northern blot analysis one week aftermassive small bowel resection. Expression increasedsignificantly by 2.8-fold between one and two weeks aftersurgery. High levels were maintained for at least onemonth after surgery. The up-regulation oftriosephosphate isomerase expression in the remnantsmall intestine after massive resection indicates that it mayplay an important role in the adaptiveprocess.