Inhibition of potato polyphenol oxidase by anions and activity in various carboxylate buffers (pH 4.8) at constant
B D Malkin1, K R Thickman, C J Markworth
1Department of Chemistry, Dartmouth College, Hanover, New Hampshire 03755, USA.
Abstract:
The activity of potato polyphenol oxidase (tyrosinase) toward DL-3,4-dihydroxyphenylalanine (K(M) 5.39 mM) was studied using a variety of carboxylate buffers at a common pH and ionic strength. Enzyme activity, greatest in citrate and least in oxalate, correlated with increasing carboxyl concentration and molecular mass. The lower activity in oxalate was attributed to more effective chelation of a copper(II) form of the enzyme by the oxalate dianion. Sodium halide salts inhibited the enzyme. Although there was little difference in inhibition between sodium and potassium salts, the degree and type of inhibition was anion dependent; K(is), values for NaCl and KCl, (competitive inhibitors) were 1.82 and 1.62 mM, whereas Na(2) SO(4) and K(2) SO(4) (mixed inhibitors) had K(is) and K(ii) values in the 250 to 450 mM range.
Related Concept Videos
Buffers
Titration of a Polyprotic Acid
Factors Affecting Activity Coefficient
The activity coefficient value for an ion is close to one when the solution has almost zero ionic strength, i.e., when the solution shows close to ideal behavior. As the ionic strength of the solution increases from 0 to 0.1 mol/L, a decrease in the...
Titration of Polyprotic Base with a Strong Acid
Protein Buffers in Blood Plasma and Cells
Certain amino acids can exist in a zwitterion state at a...
Titration of Polyprotic Acids with a Strong Base


