Occurrence of peptidyl D-amino acids in soluble fractions of several eubacteria, archaea and eukaryotes.

The occurrence of peptidyl D-amino acids in the aqueous soluble fractions was investigated in various eubacteria, some archaea and some eukaryotes. The contents of the D-enantiomers of serine, alanine, proline, glutamate (glutamine), aspartate (asparagine) and phenylalanine were determined with cell- and tissue-extracts, by means of acid hydrolysis and high-performance liquid chromatography. The rate of D-enantiomer (%, the ratio in molar concentration of a D-amino acid to the total of the D-amino acid and the corresponding L-amino acid) of alanine and glutamate were high in some Gram-positive eubacteria: 11.7% in Staphylococcus epidermidis and 10.3% in Streptococcus pyogenes for alanine, and 22.3% for glutamate in Bacillus YN-1. The D-glutamate content was also high (8.0%) in the Gram-negative eubacterium, Thiobacillus ferrooxidans. D-Aspartate was common, as was D-glutamate: the highest D-aspartate content was detected in an archaeum, Pyrobaculum islandicum (4.0%). However, the content of D-aspartate was low, 0.2-1.8% in most other bacteria. The presence of D-serine was shown in some organisms, but that of D-proline was scarce. The D-enantiomer of phenylalanine was not detected in any of the organisms examined. These results indicate that of the bacteria examined herein most Gram-negative and some Gram-positive eubacteria, as well as archaea contain only low levels of D-amino acids in the soluble peptidyl fraction, and the levels were comparable to those in eukaryotes examined. To our knowledge, the general presence of peptidyl D-amino acids in these organisms, especially archaea and eukaryotic cells including those from rat liver tissues, has been shown here for the first time.