enzyme regulation Flashcards
what are the 3 ways you can regulate an enzyme by reversible covalent modification?
- cause conformational change that affects catalysis
- alter cell localization of enzyme
- alter interactions with other proteins
glycogen phosphorylase is an example of what type of regulation?
reversible covalent modification
zymogens becoming activated by cleavage by another protease go onto synthesize and activate other enzymes. what type of regulation is this an example of?
regulation of irreversible covalent modification
maintenance of blood clotting cascade is an example of what type of regulation?
irreversible enzyme activations
what three rapid responses are needed to maintain blood volume following a blood vessel injury?
- rapid activation of blood coagulation
- localization of clot to site of injury
- rapid termination after clot formation to prevent thrombosis
what is the classification of most of the enzymes in most of the blood clotting cascade?
serine proteases
localization of the clot in the coagulation cascade is what type of regulation?
reversible covalent modification
what part of the coagulation cascade is vitamin K involved in?
the localization of the clot to site of injury
it is a co-factor for the enzyme that catalyzes the addition of the y-carboxyl group
how does coumadin and warfarin (anti-coag drugs) act on the coagulation cascade?
they mimic vit K so they are able to get into and act as competitive inhibitors to enzymes that would normally be involved in the y-carboxyglutamate modification step
how is the clotting cascade terminated?
by an opposing cascade involving another serine protease-plasmin. “reverse zymogen activation cascade”
how does plasmin work?
by hydrolyzing peptide bonds in the fibrin clot, breaking it up
what serine protease can be administered after the onset of MI symptoms?
TPA (tissue plasminogen activator)
what is the action of pancreatic trypsin inhibitor?
substrate that binds very tightly to the active site of trypsin
what is the action of alpha-antitrypsin
inhibitor of elastase-protects tissues from elastase secreted by neutrophils
what type of inhibitor is anti-thrombin?
serpin-serine protease inhibitor
how does the presence of heparin effect ATIII
ATIII binds very poorly to the proteases (which cleaves it so that it can go onto irreversibly inhibit an enzyme) unless heparin is present
what characterizes an ATIII deficiency/
excessive clotting (thrombosis) often in legs and lungs
list some characteristics of a1-antitrypsin deficiency
too much active elastase in lung eventually causes COPD
patient cant inhibit elastase and is plagued with SOB
severe deficiency is often accompanied by liver disease
How is protein kinase A regulated?
Interaction of cAMP with regulatory subunits - releases inhibition by regulatory subunits and activates catalysis
In order to determine how much enzyme is present, what data do clinical labs usually use?
Rate of product formation over time
In an assay measuring product, what would be added in excess?
-EXCESS SUBSTRATE
Why do we measure the rate of the rxn at saturating substrate concentration if we want to determine how much enzyme is present?
Because at the Vmax (saturating substrate concentration) - the rate of the rxn is directly proportional to the amount of enzyme present
-[detla S] and [delta P] are linear
When would a coupled enzyme assay be used?
When direct measurement of the specific products is not possible
In a coupled enzyme assay, what should be added in excess?
Substrates for BOTH of the reactions taking place
What is the goal of performing a coupled enzyme assay?
You are measuring the products of the second reaction in order to calculate the amount of enzyme present in the first reaction
When measuring metabolites or drug levels, what is the goal of the assay?
- You must use an enzyme specific to that small molecule in the complex mixture
- You are measuring the amount of product formed to quantitate this substance
What would you add in excess to a metabolite or drug level enzyme assay?
-excess ENZYMES and other substrates involved in the reaction
In a blood glucose coupled enzyme assay, what is detected and how?
NADPH by its ability to reduce a colored dye to form a colored product - dipstick
Why do non-plasma specific enzymes appear in the plasma?
- damage to tissue of origin
- spillover due to overproduction
- tumor
How are non-plasma specific enzymes detected in the plasma?
- level of enzyme activity
- timing of appearance of activity
- presence of tissue-specific isozymes
What does alanine aminotransferase - ALT in the plasma mean?
Viral hepatitis
What does amylase in the plasma mean?
acute pancreatitis
What does creatine kinase in the plasma mean?
- MI
- muscle disorders
What does LDH 5 in the plasma mean?
-Liver diseases
What does lipase in the plasma mean
acute pancreatitis
What does phophatase acid in the plasma mean?
Metastatic carcinoma of the prostate
What does phosphatase alkaline isozymes in the plama mean?
- Various bone disorders
- obstructive liver disease
What three enzymes in the plasma indicate MI?
- CK2
- LDH1
- aspartate aminotransferase AST
-These all appear transiently after an MI
What else is important besides the presence of certain enzymes in the plasma to diagnose an MI?
The timing of their rise and fall - need to measure the enzyme levels at multiple times
What is the definition of an isozyme?
Different forms of an enzyme that carry out the same reaction - they have different AA sequences, chemical properties and enzymatic characteristics
How can different isozymes be distinguished?
- charge difference - electrophoresis
- specific monoclonal antibodies
- differences in enzymatic properties or inhibitor sensitivities
What enzymes would be present in the plasma in a patient with muscular dystrophy?
- CK3
- long term rise in plasma CK over weeks
