Phenylalanine hydroxylase: possible involvement in the S-oxidation of S-carboxymethyl-l-cysteine.

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Boonyapiwat B, Forbes B, Steventon GB

Phenylalanine hydroxylase: possible involvement in the S-oxidation of S-carboxymethyl-l-cysteine.

Anal Biochem. 2004 Dec 1;335(1):91-7. doi: 10.1016/j.ab.2004.08.003.

PubMed ID

15519575 [ View in PubMed

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Abstract

Activated phenylalanine 4-monooxygenase, phenylalanine hydroxylase (PAH), is known to be involved in the S-oxidation of a number of sulfide compounds. One of these compounds, S-carboxymethyl-l-cysteine (SCMC), is currently used for the treatment of chronic obstructive pulmonary disease and otitis media with effusion as a mucolytic agent, and the S-oxides are the major metabolites found in urine. However, the enzyme catalyzing the S-oxidation of SCMC has yet to be identified. Here we report on the role of nonactivated phenylalanine 4-monooxygenase activity in rat liver cytosol in the S-oxidation of SCMC. Linearity of the enzyme assays was seen for both time (0-16 min) and cytosolic protein concentration (0.1-0.5mg/ml). The calculated K(m) and V(max) values for the formation of SCMC (S) S-oxide were 3.92+/-0.15 mM and 1.10+/-0.12 nmol SCMC (S) S-oxide formed/mg protein/min, respectively. The calculated K(m) and V(max) values for the formation of SCMC (R) S-oxide were 9.18+/-1.13 mM and 0.46+/-0.11 nmol SCMC (R) S-oxide formed/mg protein/min, respectively. These results indicate that in the female Wistar rat, nonactivated PAH showed a stereospecific preference for the formation of the (S) S-oxide metabolite of SCMC against the (R) S-oxide metabolite of SCMC.

DrugBank Data that Cites this Article

Drug Enzymes

Drug	Enzyme	Kind	Organism	Pharmacological Action	Actions
Carbocisteine	Phenylalanine-4-hydroxylase	Protein	Humans	Unknown	Substrate	Details