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Various D-amino acids play important physiological roles in mammals, but the pathways of their production remain unknown except for d-serine, which is generated by serine racemase. Previously, we found that Escherichia coli cystathionine β-lyase possesses amino acid racemase activity in addition to β-lyase activity. In the present work, we evaluated the enzymatic activities of human cystathionine γ-lyase, which shares a relatively high amino acid sequence identity with cystathionine β-lyase. The enzyme did not show racemase activity toward various amino acids including alanine and lyase and dehydratase activities were highest toward L-cystathionine and L-homoserine, respectively. The enzyme also showed weak activity toward L-cysteine and L-serine but no activity toward D-amino acids. Intriguingly, the pH and temperature profiles of lyase activity were distinct from those of dehydratase activity. Catalytic efficiency was higher for lyase activity than for dehydratase activity. [ABSTRACT FROM AUTHOR]