Amphioxus allantoicase: molecular cloning, expression and enzymatic activity.

Allantoicase, one of the purine metabolism enzymes, is progressively truncated during the chordate evolution, yet it is unknown when its activity became phylogenetically extinct. In this study, a cDNA encoding allantoicase was isolated from the gut cDNA library of amphioxus Branchiostoma belcheri tsingtauense. It is 2441 bp long, and contains an open reading frame encoding a protein of 392 amino acid residues. RT-PCR analysis showed that amphioxus allantoicase was strongly expressed in the hepatic caecum, and weakly expressed in other tissues including hind-gut, gill, muscle, notochord, testis and ovary. The parallel experiment was performed measuring the allantoicase activity in the same tissues revealed that its activity was high in the hepatic caecum, but low or undetectable in other tissues examined. These suggest that allantoicase remains in action in the primitive chordate amphioxus.