Factors Affecting Polyphenol Oxidase Activity

Flashcards covering the enzymatic principles, substrate specificity, chemical nature, and temperature effects on Polyphenol Oxidase.

Polyphenol Oxidase (PPO)

A copper-containing enzyme with an optimum pH of $6.7$ that catalyzes the oxidation of di- and tri-hydroxy phenols to their corresponding quinones.

Active Site

The region on an enzyme, composed of a unique combination of amino acid residues (side chains or R groups), where the substrate binds.

Absolute Specificity

A type of enzyme specificity where the enzyme will catalyze only one specific reaction.

Group Specificity

A type of enzyme specificity where the enzyme acts only on molecules containing specific functional groups, such as amino, phosphate, or methyl groups.

Linkage Specificity

A type of enzyme specificity where the enzyme acts on a particular type of chemical bond regardless of the rest of the molecular structure.

Stereochemical Specificity

A type of enzyme specificity where the enzyme acts on a particular steric or optical isomer.

Phenylthiourea

A compound with a very strong chemical affinity for copper, which acts as the essential cofactor for polyphenol oxidase.

Phenol (Substrate Specificity)

A mono-hydroxyl phenol that does not serve as a substrate for polyphenol oxidase because the enzyme only acts on di- or tri-hydroxyl phenols.

Hydroquinone (Substrate Specificity)

A di-hydroxyl phenol that slightly alters the enzyme active site configuration via the induced fit model, producing a faint color change upon reacting with PPO.

Optimum Temperature

The specific temperature at which the activity of an enzyme reaches its maximum rate.

Thermal Denaturation

The breaking of non-covalent bonds by high temperatures, leading to protein denaturation, precipitation, and loss of enzymatic function.

Polyphenol Oxidase Oxidation Reaction

The reaction mechanism where polyphenol oxidase oxidizes phenols in the presence of oxygen to produce water and quinones: $\text{Phenol (Phe)} + \frac{1}{2}\text{O}_2 \rightarrow \text{H}_2\text{O} + \text{Quinone}$

Di-hydroxyl Phenols Structures

Chemical structures including Hydroquinone, Catechol, and Phenol used to test the substrate specificity of Polyphenol Oxidase.

Degree of Color Intensity Symbols

Qualitative scoring system for enzymatic color change: Symbol - indicates no color change (colorless), + indicates faint color (just detectable), ++ indicates definite color, and +++ indicates dark (deep) color.