Occurrence of D-amino acids and a pyridoxal 5 '-phosphate-dependent aspartate racemase in the acidothermophilic archaeon, Thermoplasma acidophilum

Free D-amino acid content in some archaea was investigated and D-forms of s everal amino acids were found in them. in the acidothermophilic archaeon, T hermoplasma acidophilum, the proportion of D-aspartate (D-Asp) to total Asp was as high as 39.7%, Crude extracts of Thermoplasma acidophilum had Asp-s pecific racemase activity that was pyridoxal 5'-phosphate (PLP)-dependent. The relative insensitivity to a SH-modifying reagent distinguished this act ivity from those of the PLP-independent Asp racemases found in other hypert hermophilic archaea (Matsumoto, M,, ct at, J. Bacteriol. 181, 6560-6563 199 9), Thus, high levels of D-Asp should be produced by a new type(s) of Asp-s pecific racemase in Thermoplasma acidophilum, although the function of D-As p in this archaeon remains unknown. (C) 2001 Academic Press.