Enzymes, Coenzymes And Isoenzymes

Enzymes, Coenzymes And Isoenzymes

Isoenzymes

• The non-protein, organic, low molecular weight & dialysable substance associated with enzyme function is known as a coenzyme
• They are regarded as the second substrate
• They participate in various reactions involving the transfer of atoms or groups
• They consist of
• Derivatives of vitamin B complex
• Organic substances
• Nitrogenous base, sugar & phosphate
• A functional enzyme is made up of apoenzyme- protein part & Coenzyme- nonprotein part
• Enzyme specificity depends on apoenzyme

“Proenzymes And Enzyme Activation”

“Proenzymes In Biological Catalysis”

 Inhibitors of enzyme action

• Inhibitors compete with the substrate & affect the enzymatic action.

Allosteric regulation of enzyme activity

• Allosteric sites are additional sites for binding of the substrate
• The enzymes possessing such sites are called Allosteric enzymes
• When a positive allosteric effector binds at the activator site, it increases the enzyme activity

“Proenzymes In Metabolic Pathways”

• When a negative allosteric effector binds at the inhibitor site, it inhibits the enzyme activity
• Allosteric enzymes exist in two states- T called tense state & R- relaxed state
• Allosteric inhibitors favor the T state while the substrate can bind only with the R form
• Allosteric enzymes give a sigmoidal curve when velocity versus substrate concentration is plotted

“Nature’S Biological Catalysts”

Allosteric regulation of enzyme activity Effects:

1. Homotropic effect

• Homotropic effect occurs when the substrate influences the substrate binding through allosteric mechanisms
• Homotropic effect is always positive

2. Heterotropic effect

• Heterotropic effect occurs when allosteric modulators affect the binding of substrate to the enzyme
• Heterotropic effect may be positive or negative