Schistosoma mansoni: Tyrosine,a putative in vivo substrate of phenol oxidase |
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Authors: | JL Seed CD Kilts JL Bennett |
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Institution: | Department of Pharmacology & Toxicology, Michigan State University, East Lansing, Michigan 48824, U.S.A. |
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Abstract: | l-Tyrosine, l-3,4]dihydroxyphenylalanine (l-DOPA), and dopamine are known to be in vitro substrates for Schistosoma mansoni phenol oxidase. Since all three compounds are present in the female schistosome, it is not clear which one serves as the substrate for phenol oxidase in intact S. mansoni. However, the concentration of l-tyrosine in the female schistosome (252 ng/mg worm) is 4-fold higher than the Km of phenol oxidase for this amino acid while the concentrations of l-DOPA and dopamine (0.954 and 0.790 ng/mg worm, respectively) are 100- and 500-fold lower than the Km of these substrates. Tri-l-tyrosine methyl ester is oxidized at less than 3% of the rate of l-tyrosine methyl ester. A tyrosine:lysine peptide and chymotrypsinogen are not oxidized. Female S. mansoni do not incorporate l-tyrosine into proteins to a significantly greater extent than l-leucine. The results suggest that free l-tyrosine is the substrate for S. mansoni phenol oxidase in vivo. |
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Keywords: | Trematode Phenol oxidase Tyrosine Dopamine |
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