On the isolation and characterization of a C-S-lyase preparation from leek, Allium porrum
1994
Lohmueller, E.M. | Landshuter, J. | Knobloch, K. (Erlangen-Nuernberg Univ., Erlangen (Germany). Inst. fuer Botanik und Pharmazeutische Biologie)
The C-S-lyase protein from leek, Allium porrum L., has been purified and characterized. The molecular mass of the native protein was determined with M=100000, including two similar subunits, M=50000. The tendency of the native protein to form a trimer, M=300000, could be supported. The isoelectric point of the enzyme turned out to be close to pH 7.5. The C-S-lyase reaction revealed a wide pH optimum, in the range of 6.1 to 6.9. The temperature optimum was found to be at 41 degrees C. Pure (+)- and (-)-isomers of S-alk(en)yl-L-cysteine sulfoxides were inserted as the substrates. The highest turnover rate was achieved with (+)-S-allyl-L-cysteine sulfoxide (alliin). (+)-S-Propyl-L-cysteine sulfoxide (PCSO) exhibited the lowest Km value. Activation energies for the cleavage of the substrates were determined to be 23kJ/mol for (+)-S-methyl-L-cysteine sulfoxide (MCSO), 38 kJ/mol for (-)-MCSO, 28 kJ/mol for (+)-alliin, and 54 kJ/mol for (+)-PCSO. On the basis of studies with specific inhibitors, pyridoxal 5'-phosphate was found to be part of the A. porrum C-S-lyase protein as a cofactor. Competitive inhibitory effects were observed with L-cysteine and related compounds.
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