Germ-free animals as tools for biomedical studies. 1: Intestinal bacterial origin of D-alanine present in urine of mutant mice lacking D-amino- acid oxidase

Abstract

The mutant mice lacking D-amino-acid oxidase excreted a large amount of alanine into their urine. Most of the alanine were found to be D-isomer. When the mice were removed from the womb just prior to birth and reared under germ-free conditions, they excreted a lower level of D-alanine. When these mice were made gnotobiotic by way of inoculation of intestinal bacteria, they again excreted the high level of D-alanine into their urine. These results indicate that the urinary D-alanine comes from intestinal bacteria. These results also indicate that the D-alanine is constantly metabolized by the D-amino-acid oxidase in normal mice, and hence indicate that one of the physiological roles of this enzyme is the metabolism of D-amino acids of the microbial origin.

D-アミノ酸オキシダーゼをもたない変異マウスは大量のアラニンを尿中に排泄し、その大部分はD-異性体であった。マウスを出生直前に胎内から取り出し、無菌条件で成育すると、低レベルのD-アラニンを排泄した。これらマウスを腸内細菌を接種しノトバイオートにすると、再び尿中に大量のD-アラニンを排泄するようになった。この結果は尿中のD-アラニンは腸内細菌に由来し、D-アラニンは正常マウスではD-アミノ酸オキシダーゼによって常に代謝され、従ってこの酵素のひとつの生理的役割は微生物起源のD-アミノ酸の代謝であることを示した。