Introduction to Enzymes and Enzymology

Study Notes

Enzymes are protein molecules that act as catalysts in living cells, speeding up biochemical reactions.
Some enzymes can be RNA molecules called ribozymes.
Enzymes exhibit high specificity, catalyzing only one type of reaction and often acting on a single substrate.
Enzymes are commercially important but their production from plants and animals is limited and often contaminated.
Microbial enzymes have advantages like large-scale production via fermentation and easy isolation if excreted into the medium.
Many enzymes are now derived from microorganisms, followed by plants and animals.

Enzymology is the study of enzymes.
Early researchers believed living things possessed a "vital force."
Justus von Liebig proposed that biological processes were caused by 'ferments.'
Wilhelm Kühne coined the term "enzyme" in 1878.
Eduard Buchner demonstrated yeast could ferment glucose to ethanol without a whole cell.

Enzyme-substrate (ES) complex forms when substrates bind to the active site.
Noncovalent interactions like ionic bonds, hydrogen bonds, and hydrophobic interactions aid substrate binding.
Substrate molecules undergo transformations within the ES complex.
Enzyme is unchanged after product formation, and its active site is available for a new substrate.

Enzyme activity varies based on pH and temperature.
Optimum pH and temperature values differ for each enzyme.
Substrate concentration affects enzyme activity:
- At low concentrations, collisions between enzyme and substrate are infrequent.
- At high concentrations, enzymes become saturated.
Michaelis-Menten equation relates substrate concentration to reaction velocity.

Enzymes are highly specific, binding only to specific substrates.
Lock-and-key model (Fischer) suggests substrates fit precisely into the active site.
Induced-fit model (Koshland) proposes the active site changes shape to accommodate the substrate.
Enzymes are very efficient, significantly accelerating reaction rates.
Enzyme activity is regulated within cells via gene control and other substances that either enhance or inhibit their activity.

Enzymes increase reaction rates without being consumed.
Enzyme-catalyzed reactions are generally reversible.
Turnover number is the number of substrate molecules processed per minute by one enzyme molecule.

Enzymes are classified into six classes based on the types of reactions they catalyze: oxidoreductases, transferases, hydrolases, lyases, isomerases, and ligases.
Specific examples and their reactions are provided (e.g., lactate dehydrogenase, nucleoside monophosphate kinase, restriction enzymes).

Enzyme inhibitors are molecules that decrease enzyme activity.
Competitive inhibitors compete with substrates for active sites.
Non-competitive inhibitors bind to sites other than active sites, altering active site conformations.

Enzyme activity can be modulated by allosteric activators and inhibitors.
Feedback inhibition occurs when a product in a reaction sequence inhibits an early step.

Enzymes act as biocatalysts in various biochemical reactions.
Their specificity and flexibility allow them to alter reaction rates based on conditions.