Study of stereospecificity in mushroom tyrosinase

This paper reports experiments on the stereospecificity observed in the monophenolase and diphenolase activities of mushroom tyrosinase. Several enantiomorphs of monophenols and o-diphenols were assayed: L-tyrosine, D,L-tyrosine, D-tyrosine; L-alpha-methyltyrosine, D,L-alpha-methyltyrosine; L-dopa,...

Full description

Saved in:
Bibliographic Details
Published in:Biochemical journal 1998-04, Vol.331 (2), p.547-551
Main Authors: Espin, J.C, Garcia-Ruiz, P.A, Tudela, J, Garcia-Canovas, F
Format: Article
Language:English
Subjects:
Basidiomycota - enzymology
catechol oxidase
Dihydroxyphenylalanine - chemistry
Dihydroxyphenylalanine - metabolism
enzyme activity
Hydrogen-Ion Concentration
Isoproterenol - chemistry
Isoproterenol - metabolism
Kinetics
Magnetic Resonance Spectroscopy
monophenol monooxygenase
Monophenol Monooxygenase - metabolism
Oxygen - metabolism
Phenols - chemistry
Phenols - metabolism
Spectrophotometry
Stereoisomerism
Structure-Activity Relationship
Substrate Specificity
substrates
Tyrosine - chemistry
Tyrosine - metabolism
Citations: Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:This paper reports experiments on the stereospecificity observed in the monophenolase and diphenolase activities of mushroom tyrosinase. Several enantiomorphs of monophenols and o-diphenols were assayed: L-tyrosine, D,L-tyrosine, D-tyrosine; L-alpha-methyltyrosine, D,L-alpha-methyltyrosine; L-dopa, D,L-dopa, D-dopa; L-alpha-methyldopa, D,L-alpha-methyldopa; L-isoprenaline, D,L-isoprenaline and D-isoprenaline. The Vmax values obtained for each series were the same. The electronic densities on the carbon atoms in the meta (C-3) and the para (C-4) positions of the benzene ring were determined by NMR assays. This value is related to the nucleophilic power of the oxygen atom belonging to the hydroxy group, which could explain the Vmax values experimentally obtained for the monophenolase and diphenolase activities of mushroom tyrosinase. The spatial orientation of the ring substituents led to lower Km values for L-isomers than for D-isomers. However, the Vmax values were the same for each series of isomers because spatial orientation did not affect the NMR value of C-4. Therefore mushroom tyrosinase showed stereospecificity in its affinity towards its substrates (Km) but not in the transformation reaction rate (Vmax) of these substrates.
ISSN:0264-6021
1470-8728
DOI:10.1042/bj3310547