Table 1.

Normalized relative activity of racemases on d- and l-amino acids

Purified enzyme	d-Amino acid or HyProa		l-Amino acida
	Amino acid	Normalized % activity ± SD	Amino acid	Normalized % activity ± SD
Alanine racemase (Alr)	Lys	100.00 ± 0.00	Lys	100.00 ± 0.00
	Arg	87.49 ± 1.64	Arg	10.79 ± 0.79
	Met	11.56 ± 0.20	Met	6.39 ± 0.22
	Gln	6.94 ± 0.09	Gln	3.07 ± 0.09
	Ala	3.10 ± 0.15	Ser	1.75 ± 0.09
	Ser	2.57 ± 0.09	Ala	1.18 ± 0.03
	Leu	1.37 ± 0.08	Asn	0.65 ± 0.08
	His	1.01 ± 0.03	Leu	0.57 ± 0.02
	Asn	0.96 ± 0.07	His	0.56 ± 0.02
	Others	NDb	Others	ND
Alanine racemase (DadX)	Ala	100.00 ± 0.00	Ala	100.00 ± 0.00
	Cys	8.35 ± 0.20	Ser	0.90 ± 0.04
	Others	ND	Others	ND
Proline racemase (ProR)	cis-d-HyPro	100.00 ± 0.00
	trans-l-HyPro	32.34 ± 0.82
	cis-l-HyPro	32.23 ± 1.82
	trans-d-HyPro	22.73 ± 0.62
	Others	ND

^aPercent activity values were normalized for the difference in derivatization efficiency between each d- and l-enantiomer (52). The final assay concentration for each amino acid was 50 mM, except for Tyr (2.21 mM) and Asp (25 mM). Assays were performed in triplicate only for those amino acids that showed detectable activity. The others category comprises all remaining chiral proteinogenic amino acids.

^bND, no activity detected.