Study of Sterospecificity in Mushroom Tyrosinase

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Study of stereospecificity in mushroom tyrosinase and the inhibiting effects of thiourea, cinnamic acid and benzoic acid

BIOL/BIOC 393 L03
Dr. Judit Moldovan

Submitted: Nov. 22nd, 2010
By: Jackie Minnick (Partners Amanda Verwoerd & Kersti Ojamaa)
Study of stereospecificity in mushroom tyrosinase and the inhibiting effects of thiourea, cinnamic acid and benzoic acid.

Jackie Minnick

This paper reports experiments on the stereospecificity observed in the monophenolase and diphenolase activities of mushroom tyrosinase and the inhibiting effects of thiourea, cinnamic acid and benzoic acid. The enantiomer L-DOPA and D-DOPA were assayed. The Vmax and Km values obtained for each were different. Thus mushroom tyrosinase showed
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The aim of this paper is the kinetic analysis of mushroom tyrosinase to study the stereospecificty in its action on both L and D DOPA as substrates. It is also the aim of this paper, to carry out a kinetic study of various inhibitors on tyrosinase activity to determine their mechanism of inhibitory effect.

EXPERIMENTAL

Methods & Materials
The procedure followed for this experiment can be found in:
J. Moldovan & B. Nilson, (2010), Lab 4 – Enzyme Kinetics, UBCO BIOL/BIOC 393, UBC Vista accessed Monday, November 8th, 2010.
No changes to the procedure were made.

Enzyme Kinetics & Calculations
Enzyme binds to a substrate molecule and catalyzes a reaction, thereby converting the substrate into product. Enzyme-catalyzed reactions proceed through an enzyme-substrate (ES) complex as shown in equation 3 (Boon, 2007).

E + S ← → ES ← → E + P (3)

Where kn represents the individual rate constants, E the enzyme, S the substrate, and P the product. When almost none of the product reverts to substrate the rate of the product formation i.e. the catalytic rate, V, is equal to k3 x [ES]. V is defined as the number of moles of product formed per second. Reaction rates are described by the Michaelis-Menton equation, shown in equation 4 (Boon, 2007).

Vo = Vmax [S] (4) Km + [S]

Where Vo represents initial reaction velocity, Vmax is maximal reaction

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