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Enzyme Activity
Enzyme Activity
Rate at which an enzyme catalyzes a
reaction.
Studied in experiments called enzyme
assays to determine:
– Turnover number – number of substrate
molecules acted on by one enzyme
molecule per minute.
– Enzyme international units – quantity of
enzyme that catalyzes the conversion of 1
µmol of substrate per minute.
Factors Affecting Enzyme Activity
•Presence of cofactors, inhibitors, modulators
and zymogen activation agents
•Presence of heavy metals (Pb, Cd, Hg…)
resulting in metal sulfide complexes
interrupting the disulfide bridges, ultimately
resulting in denaturation of the native state.
Factors Affecting Enzyme Activity, Con’t.
• pH – enzymes have optimum pHs, above and
below which the rate decreases.
•Change in pH of
the environment
results in a change
in the rate of
catalysis
Denatured
Factors Affecting Enzyme Activity, Con’t.
• Enzyme concentration – the more enzyme
present, the faster substrate reacts.
Factors Affecting Enzyme Activity, Con’t.
• Increasing substrate concentration – increases
the reaction rate until enzymes become
saturated (Vmax).
•Enzyme
concentration
does not affect
the
concentration
of reactant or
products, only
rate of reaction
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Factors Affecting Enzyme Activity, Con’t.
• Temperature – enzymes have an optimum
temperature, above which they begin to
denature.
Enzymes of the Gastrointestinal Track
(Digestive System)
Enzyme
Catalyzes
Activation
Mouth:
•Amalyase
Enzyme
saliva
proteins
H+
Stomach:
Biological
activity
maximum
is between
33 and 42oC
•Peptidases
starches
•Pepsin
Pancreas/ Sm. Intestine:
•Lipases
Catalyzes
Activation
proteins
Trypsin
Autoactivated
Chymotrypsin
Trypsin
Carboxypeptidase
Trypsin
Trypsin, pepsin, and chymotrypsin all
cleave peptide bonds in proteins and are
endopeptidases
Antibiotics
•Penicillin
Inhibitor that inhibits the formation of
structurally sound cell walls in bacteria
Since humans lack cell walls, it does
not inhibit human enzyme functions
Penicillin along with its derivatives are
used to slow bacteria growth until our
body’s defenses can take on the
attacker.
lipids
Autoactivation
•Endopeptidases catalyze
the hydrolysis of peptide
bonds on interior amino
acid residues but not
terminal residues.
•Enzymes that hydrolyze
terminal amino acid
residues are called
exopeptidases.
Medical Applications
• Changes in blood serum concentrations of
specific enzymes can be used to detect cell
damage or uncontrolled growth (cancer).
• The measurement of enzyme concentrations
in blood serum has become a major
diagnostic tool, particularly in diagnosing
diseases of the heart, liver, pancreas,
prostate, and bones.
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Medical Applications, cont.
Medical
Applications, cont.
• Isozymes are slightly
different forms of the
same enzyme
produced by different
tissues.
• Serum levels of
isozymes can be used
in the diagnosis of a
wide range of
diseases.
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