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

Abstract

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.