The pyridoxal-catalyzed elimination of hydrogen sulfide or methyl mercaptan from -amino acids such as L-cysteine, S-methyl-L-cysteine, and dlmethionine was studied quantitatively in ah atmosphere of nitrogen at 100°C and at pH 5.8 or 6.2 in the presence and absence of Al(III), Fe(III), Fe(II), Sn(IV), and Sn(II). The catalytic activity of the metal ions decreases in the order Al(III) » Fe(III) > Fe(II) » Sn(IV) « Sn(II) in the case of L-cysteine. With S-methyl-L-cysteine, the order is

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