Enzymes Flashcards
ACE inhibitors
- Angiotensin converting enzyme inhibitors
* ** ACE constricts blood vessels to raise BP in addition to converting angiotensin I to angiotensin II which triggers release of aldosterone from the kidney—>raising blood pressure even more - cease the ACE pathway, preventing BP elevation
Zymogens
Inactivated form of enzymes
Enzymatic Functions/Properties
Functions:
- increase rate of reaction by lowering activation energy
- stabilize transition states
- provide a favorable miroenvironment in terms of charge or pH
Properties:
- Substrate-specific
- T & pH dependent
Be Aware
I. Do not impact the thermodynamics or position of equilibrium of a rxn II. are not consumed or changed in a rxn
Enzyme Specificity
an enzyme property that explains the ability of enzymes to only catalyze rxns that involve a specific group of substrate
Enzyme Types
6 types of enzymes exist: HILLOT
- Hydrolases
- Isomerases
- Ligases
- Lyases
- Oxidoreductases
- Transferases
HILLOT
Oxidoreductases
- One type of enzyme that catalyzes oxidation-reduction rxns
- Often have cofactors like NAD & NADP that act as electron carriers
- may have dehydrogenase, reductase or oxidase as part of their name
Include both oxidants & reductants
Oxidants
electron acceptor in an oxidation-reduction rxn
Reductants
electron donors in an oxidation-reduction rxn
Transferases
One group of enzymes that catalyze transfer of a functional group from one molecule to another.
Kinases make a member of this category of enzymes!
Kinases
Transferases that move a phosphate from from ATP to another molecule.
Hydrolases
- A group of enzymes that break down a compound into 2 molecules using the addition of water.
- are named for their substrates;
I: phosphatases –>cleave phosphate
II: nucleases–>cleave nucleic acids
III: peptidases–>cleave peptides
IV: lipases–>cleave lipase
Liases (AKA Synthases)
- Category of enzymes that catalyze cleavage of one substance into two products while also catalyzing synthesis of a single substance from two reactants.
- Does not require H2O and does not catalyze oxidation-reduction rxns.
Isomerases
Group of Enzymes that catalyze rearrangement of bonds within a molecule, but can also act as transferases, oxidoreductases, and lyases.
***Catalyze rxns involving both stereoisomers and constitutional isomers.
Ligases
Enzymes that catalyze addition and synthesis rxns involving large molecules and often involve the use of ATP.
**Synthesis of smaller substances is often catalyzed by lyases.
Enzymes Grouped Based on Functional Similarity
- Lyases & Ligases (Both involved in synthesis–Lyases synthesize smaller substances whereas Ligases synthesize larger substances and involve usage of ATP)
- Isomerases & [transferases, oxidoreductases & hydrolases]
Thermodynamics
A function that relates the energy states of the reactants and products of a rxn
- -if E of R > E of P– G>0 —Rxn is Endergonic
- -if E of R < E of P– G<0 —Rxn is Exergonic
Enzyme-Substrate Complex
Compound formed as a result of a substrate’s bond with the active site of an enzyme whose formation stabilizes the transition state and reduces activation energy of a rxn
Is stabilized by
- H-bonds
- Ionic bonds
- Transient covalent bonds
Enzyme-Substrate Interaction Theories
- Lock-Key Theory
2. Induced Fit Model
Lock Key Theory
One of the theories that attempts to explain the relationship b/w an enzyme and a substrate; it describes an enzyme’s active site as a lock and the substrate as a key
***According to this theory, no alterations have to be done in the tertiary or quaternary structures of either the substrate or the enzyme
Induced-Fit Model
One of the theories that explains the relationship b/w an enzyme and a substrate.
According to this theory, the proper substrate’s binding to an enzyme’s active site induces conformational changes in the enzyme that allow it to fully wrap around the substrate; thus lowering the activation energy of the rxn.
Conformational change of the enzyme is endothermic while release of the product by the enzyme is exothermic
Cofactors/Coenzymes
- Small, non-protein compounds that bind to an enzyme’s active site to help the enzyme catalyze a rxn!
- They can function by carrying charges!
- They are stored in small quantities
if absolutely necessary for an enzyme to carry out it’s function, they’re called prosthetic groups
[coenzymes: organic compounds such as vitamins, NAD, FAD, & Coenzyme A]
[Cofactors: inorganic minerals like iron]
They are not specific to a single rxnMultiple cofactors can be used for catalyzing a single rxn**
Holoenzymes
Enzymes containing co-factors
Apoenzymes
Enzymes not containing co-factors
Water-Soluble Vitamins
Vitamins B complex & Vitamin C (Ascorbic Acid)—coenzymes that must be replenished quickly
Fat-Soluble Vitamins
Vitamins A, D, E, K - can be stored in the body
Vitamin Bs
B1: Thaimine B2: Riboflavin B3: Niacin B5: Pantothenic Acid B6: Pyridoxal Phosphate B7: Biotin B9: Folic Acid B12: Cyanocobalamin
Factors that Impact Enzyme Kinetics
Enzyme kinetics refers to the rate of a rxn (V).
Factors that impact Enzyme Kinetics:
- [E]—Enzyme Concentration
- [S]–Substrate Concentration
- pg 48; fg 2.4 of Biochem*
- Increasing [S], increases rate of enzymatic catalysis & the rate of the rxn*
Maximum Velocity [Vmax]
highest rxn velocity in enzyme kinetics that can be obtained in a rxn by having all enzymatic active sites saturated by substrates.
At and beyond Vmax, the rxn rate is independent of [S]
Michaels Menton Equation
Enzyme Kinetic Equation that indicates how change in [E] & [S] changes rate of a rxn [V] that is being catalyzed by enzymes
k1 k3
E + S ==> ES ==> E + P
<==
k2
When [E] is constant—> V= (Vmax* [S])/(Km + [S])
at 1/2 (Vmax) , Km= {S] = 1/2 [E]’s active sites are
occupied by substrates
pg48, Biochem
Michaelis Constant / Km
Substrate concentration in Enzymatic Kinetics at which half of enzymatic active sites are occupied by substrates. Differs for various enzymatic rxns b/c it depends on enzyme affinity for substrate
Is a measure of Enzymatic affinity for substrates
Enzymatic rxn Rates at Various Points of a rxn
- below Km, rxn rate increases remarkably with increased [s]
- above Km but before Vmax is reached, rxn rate increases more slowly with increase in [S]
- at Vmax, rxn rate does not change with increase in [S]
Lineweaver-Burk Plot
Double reciprocal linear graph of the Michaelis-Menton equation that can be used to determine the type of enzymatic inhibition affecting a rxn b/c this graph provides factual values of Km & Vmax
-1/km: is the intercept of the graph with the x-axis
1/vmax: is the intercept of the graph with the y-axis
Michaelis Menten Plot
Plot of Michaelis Menten equation– V (X) vs. [S] (Y-axis)
Can be either:
- Hyperbolic–if enzyme has one active site
- Sigmoidal–if enzyme has multiple active sites with
multiple subunits that allow cooperativity-
-transitions b/w T(tense) & R(relaxed)
states
Factors that Impact Enzymatic Activity
- T–E activity doubles for every 10degrees C increase
until optimal T is reached [37C, 98F or 310K]–
above such Ts, E denatures - pH–optimal physiological pH is 7.4–if exposed to
more acidic or basic pHs, E denature. - Salinity/Osmolarity–changes in [salt] can disrupt H &
ionic bonds, can cause minor E conformation
changes, or can lead to E denaturation
Exceptions for #2: Trypsin: stomach enzyme functions best at pH=2; Pancreatic enzymes in the small intestine function best at pH=8.5*
Enzymatic Regulation Methods
1. Feedback Regulation/Inhibition
I: Reversible Inhibition
1. Competitive
2. Noncompetitive
3. Mixed
4. Uncompetitive
II: Irreversible
2. Feed-Forward RegulationFeedback Inhibition
An enzymatic regulation technique where a product of a biosynthetic pathway is used to turn off the pathway by binding to multiple enzymatic active sites
Competitive Inhibition
A reversible method of enzymatic regulation where a given quantity of inhibitors compete with substrates for enzymatic active sites.
Increases the value of Km but leaves Vmax intact on a Lineweaver-Burk Plot
Non-Competitive Inhibition
A reversible method of enzymatic regulation where inhibitors induce conformational changes in enzymes by binding to enzymatic allosteric sites, preventing enzymes from forming ES complexes and from catalyzing rxns.
decreases the quantity of available enzymes for catalytic rxns, leads to a decrease in Vmax as a result but leaves Km constant.
***inhibitor can bind to either E or ES complex.
Mixed Inhibition
A reversible method for enzymatic regulation where inhibitors bind to allosteric sites on either E or ES depending on their affinities for each.
Decreases Vmax but may increase or decrease Km depending on inhibitors’ affinities for E vs. ES.
- Km inc if inhibitor binds to E*
- Km dec if inhibitor binds to ES*??? WHY?
on Lineweaver-Burk plot, the points of intersections for -1/km or 1/vax are not on either axis
Uncompetitive Inhibition
A reversible method of enzymatic regulation where inhibitors bind to an allosteric site in ES complexes only, locking S in E and preventing its release.
Decreases both Vmax & Km.
***Curves on Lineweaver-Burk plot are parallel.
Irreversible Inhibition
An enzymatic regulation technique that results in permanent alteration of the enzyme or inactivation of its active site.
Is involved in drug mechanisms.
EnZymes that Can be Regulated
- Allosteric E
- Covalently Modified E
- Zymogens
Allosteric Enzymes
Enzymes with multiple subunits that transit b/w R & T phases; are regulated by either activators or inhibitors that bind to allosteric sites, causing a conformational change that either make the active sites more available or less available.
Covalently-Modified Enzymes
Enzymes that become active or inactive through covalent-linkages with other molecules.
Examples of covalent modifications/linkages:
- Phosphorylation/dephosphorylation
- Glycosylation
Zymogens
Enzymes with an active and a regulatory site that stay inactive until the regulatory site is removed and the active site is exposed.
Ex: digestive enzymes such as trypsinogen
