regulation of enzymes

Question 1

What is themichealis menton equation

Answer 1

1. MM measured the change in velocity with respect to change in [S]
   
   1. Velocity of enzyme have linear realationship with [s]
      
      1. activity/min
         2.

Question 2

express the relationship/difference between enzyme 1/2

Answer 2

1. Km= 1/2Vmax,
   
   1. value that reflects the affinity of the enzyme
   2. smallKm= high affinity
   3. high Kn=low affinity

Question 3

draw and explain values in the line weaver burk plot

give advatages over the use of michealis-menton

Answer 3

1. advatages
   
   1. requires less point to make a plot
   2. make the extrapolation easier
   3. Km and Vmax can be calculated from the interception on abscissa and ordinate, respectively

Question 4

What isozymes are involved with glucose managment. define location/function and relationship.

Answer 4

1. isozyme- different proteins that share simillar function
   
   1. hexokinase
      
      1. location
         
         1. RBC
      2. function
         
         1. allows RBCs to use glucose when its plasma level is low
   2. glucokinase
      
      1. location
         
         1. liver and pancreatic beta cells
      2. function
         
         1. promotes storage of glucose or insulin secretion. when glucose is high in plasma.

diagram

1. glucose P-lation in the liver
   
   1. up as blood G increases
   2. down as Blood G falls
   3. high Km of hepatic glucokinase promotes glucose storage

Question 5

what are inhibitors ?

list two types and decribe types of inhibition mechanisms. include affects mathematical values.

Answer 5

inhibitor-dimishes the velocity of an enzyme reaction

1. reversible
   
   1. noncovalent interactions
      
      1. enzyme may regain function
2. irreversible
   
   1. covalent
      
      1. enzyme needs to be replaced
         
         1. degraded and made again
         2. covelent interaction seized
      2. example
         
         1. phosphorylation
            
            1. phosphorylating enzymes turns them on/off
         2. ADP-ribosylation
            
            1. targets amino acids leading on/off, or malfunction-> disease

types of inhibition

1. competative
   
   1. binds to active site
   2. Vmax unchanged
   3. Km increases
2. noncompetative
   
   1. binds allosterically or ES complex
   2. Vmax is decreased
   3. Km unchanged

Question 6

Physostigmine acts against acetylcholine esterase enzyme, but is over come by increasing the substrate.

If a statin drug acts similarly to HMG-CoA reductase, reducing cholesterol synthesis how are these enzymes overcome by substrate addition.

diagram in MM and LWB

Answer 6

1. competative inhibition
   
   1. inhibitor binds to the same site as substrate
   2. inhibitor can be reversed by HIGH [S]
2. values that change
   
   1. Vmax does NOT change
      
      1. the enzyme can STILL reach Vmax
   2. Km is increased
      
      1. b/c more substrate is needed to achieve 1/2Vmax

Question 7

Drug Q acts against an enzyme and adding more substrate will not overcome the inhibitor.

What type of inhibitor is this ? diagram in MM and LWB

Answer 7

1. noncompetative inhibition
   
   1. inhibitor binds on allosteric sites and or ESC
2. values that change
   
   1. Vmax is lowered
      
      1. substrate addition will not overcome the inhibitor
   2. Km does NOT change
      
      1. inhibition does not interfere with substrate binding to the enzyme

Question 8

The image shows phosphofructokinase-1 and glycogen phosphorylase action. What is the photo highlighting?

Answer 8

these enzymes are controlled allosterically by products. products and substrates increase and decrease their function

they are also rate-limiting enzymes controlled by change in conformation of catalytic site.

1. phosphofructokinase-1
   
   1. irreversible transferase of phosphorus from ATP to fructose-6-phosphate
   2. allosterically activated by
      
      1. fructose 2,6-bisphosphate
2. glycogen phosphorylase
   
   1. rate limiting enzyme for glycogenolysis
   2. allosterically activated
      
      1. AMP

Question 9

discuss the two models of allosteric regulation with regard to how the substrates load. give example

Answer 9

there are two models of allosteric regulation

1. sequential progression-“step wise”
   
   1. binding of one molecule triggers conformation of another subunit. This continues until T <->R
   2. “theres a sequence or step by step model”
2. concerted progression-“all or none”
   
   1. binding of substrate to one subunit facilitates binding of another.
      
      1. cooperativity for Hb
         
         1. enzyme in T conformation->1st item binds->changing the configuration and increasing the affinity->more items bond

Question 10

Allosteric activators and inhibitors bind on the enzyme outside of the active site. What advantages do allosteric activators and inhibitors offer the enzyme?

What does the look like in a mechalis-menton graph? Diagram the normal, addition of activator/inhibitor. Explain

Answer 10

advantages

• inhibitors have stronger effect when compared to compettive/noncompetative
  
  • comp/noncomp work on the active site
• 1. normal
  1. Binding of substrate stabilizes the active conformation, allowing the second substrate to bind more readily
     2. activator
  2. stabilize the R-state
     
     1. this has a higher affinity for the substrate
  3. hyperbolic
     3. inhibitor
  4. stabilize the T-state
     
     1. low affinity for the substrate
  5. shifts the curve to the right

Question 11

I had food contaminated with cholera, leading to illness. What is the mechanism and explain function.

Answer 11

cholera toxin is a type of ADP-ribosylation

1. targets
   
   1. covalently binds R and K in G proteins
      
      1. locking in the on state
2. disease
   
   1. increases water secretion into intestinal lumen leading to dehydration

Question 12

A child is in a state of hypoglycemia, many people in the complex were really sick. This child has not received any vaccines.

what could it be and explain mechanism

Answer 12

pertussis generate a toxin that acts to ADP-ribosylation of

1. target
   
   1. covalently modifies R, K in G-proteins
   2. locking it in the inactive state
2. disease
   
   1. leads to increase insulin release by pancrease->hypoglycemia

Question 13

Jane feels really tired when she jogs. She is concerned all the extra weight she gained is making her tiered. She has low blood glucose and was diagnosed with anorexia nervosa.

What enzymes and agents are at play with Janes conditions?

Answer 13

increased working out leads to use of ATP generating AMP.

1. AMPinitiates the feedback mechanism. It is an allosteric stimulator for phosphofructokinase-1 and glycogen phophorylase.
   
   1. ATP/AMP ratio inhibits and stimulates allosterically, respectivly
2. she does not have enough fuel stored to supply the energy demand and is easily fatigued.

Question 14

Some enzymes require cofactors.

Describe the relationship with the glycogenolysis rate limiting enzyme.

Answer 14

glycogen phosphorylase is the rate-limiting enzyme

1. requires B6
2. activated
   
   1. AMP
      
      1. allosteric activator
   2. phosphorylation
      
      1. phosphorylation kinase, transferase, phosphorylates GP in response to adrenaline

Question 15

describe the function/mechanism/example of the conformation changes in:

1. calmodulin
2. G proteins

Answer 15

1. calmodulin- conformation/protein-protein
   
   1. a Ca2+ binding protein
   2. function
      
      1. regulates different protein targets
   3. mechanism
      
      1. Contains four binding sites for Ca2+
      2. binding of Ca2+ leads to conformational changes
   4. example
      
      1. Ca2+ is released from ER, in hepatocyte, activating calmodulin. Then calmodulin activates glycogen phosphorylase kinase, which phosphorylates(activates )glycogen phorphorylase.
         
         1. a key enzyme in glycogenolysis
2. G proteins
   
   1. physically activates the target protein, when bound
   2. function
      
      1. act as signaling agent
   3. mechanism
      
      1. G-GTP associates with target protein, this activates target protein, then regulator of G protein signaling stimulates the G-GTP to hydrolyze to G-GDP, seperating and inactivating the target protein and G protein.
   4. target of disease like whooping cough

Question 16

How is PKA used to define protein-protein interactions of regulatory enzymes?

Answer 16

PKA is inactive with R subunit attached. The R subunit has a cAMP binding site, when bound by cAMP it undergoes physical conformation releasing PKA. When PKA is released it can then act to phorphorylate various targets

1. this is an example protein-protein interaction in the use of signal amplification

Question 17

Describe how digestive and clotting enzymes are activated.

Answer 17

These are examples of proteolytic cleavage, these enzymes need subunits cleaved from them in order to activate.

1. Digestive enzymes are secreted as zymogens/proenzymes
   
   1. enteropeptidase hydrolyzes trypsionogen -> generating active trypsin
      
      1. trypsin activates other pancreatic proteases including itself
2. blood coagulation-damage of vessels activates the zymogens in the blood
   
   1. prothrombin ->thrombin, which digests fibrinogen to fibrin leading to clot formation

Question 18

pyruvate dehydrogenase is always being generated in the cell. This enzyme is considered a ______. Describe other regulations in protein synthesis

Answer 18

rate of reaction is proportional to the amount of enzyme present. Regulating the protein controls how much of a reaction happens.

1. regulation techniques include
   
   1. rate of gene expression
      
      1. unduction/repression
   2. mRNA stability

pyruvate dehydrogenase is a housekeeping gene, not usually regulated or altered

Question 19

Jerry is not eating for 3days in reserve of a religious holiday. How are is his protein managed?

Answer 19

regulated protein degredation

1. brought on by
   
   1. fasting
   2. infection
2. mechanism
   
   1. proteasomes are activated in both states, highly selective process
      
      1. porteins distained for defradation are ubiquinated, activated by cortisol.
      2. once polyubiquinated, proteins are degradated
      3. freed AA’s are used for gluconeogensis and/or antibody generation
         
         1. fasting=gluconeogenesis
         2. infection=antibody generation/other immune needs
            4.

Question 20

Answer 20

Question 21

inhibitor/activators regulate metabolic pathways through

1. 2. 3.

Answer 21

1. rate limiting steps
   
   1. controlling the irreversible step in a reaction will control which way a product generation goes
2. feedback and feed-forward regulation.
   
   1. allow for variation in control of mechanism
3. tissue isozymes
   
   1. same function, different kinetics
      
      1. hexokinse in RBC, glucokinase in liver

Question 22

Explain regulation of enzyme activity by conformational changes

• give examples of different types of conformational changes
• which enzymes are controlled by this mechanism?

Answer 22

1. conformational changes
   
   1. allosteric activation or inhibition
      1. phosphofructokinse;F2,6P
      2. glycogen phosphorylase;AMP/ATP ratio
   2. phosphorylation or other posttranslational modifications
      
      1. covalent modifications
         
         1. phosphorylation
         2. ADP-ribosylation
   3. protein-protein interacions
      
      1. interaction can change a conformation
         
         1. PKA: cAMP releases it from it repressive subunits
   4. proteolytic cleavage
      
      1. enzymes that must have a section cleaved off to be turned on/off.
         
         1. enteropeptidase acts on trypsionogen->active trypsin
         2. prothrombin->thrombin
2. most rate-limiting enzymes are controlled by change in conformation of catalytic site

Question 23

What is an allosteric enzyme? Describe regulation of allosteric enzymes

Answer 23

1. allosteric enzyme
   
   1. an enzyme that changes their conformation upon binding an effector
2. activators and inhibtors
   
   1. can bind to the allosterisite
   2. can cause conformational changes that affect affinity for substrate
3. example
   
   1. phosphofructokinase
      
      1. allosteric activator
         
         1. F-2,6-P2
   2. glycogen phosphorylase
      
      1. allosteric activator
         
         1. AMP

Question 24

explain regulation of enzyme activity by posttranslational modifications

• give examples of modification and affected proteins

Answer 24

addition of moiety to amino acid after translation

1. many enzymes are regulated through covalent modification
   
   1. examples
      
      1. phosphorylation
         
         1. Target S, T or Y residues
         2. can prevent or promote protein-protein interaction
         3. can activate or inhibit enzyme
            
            1. example
               
               1. glycogen phosphorylase = increase
               2. glycogen synthase=decrease
      2. ADP-ribosylation
         
         1. ribosylation of R and K residues by bacteria
            
            1. cholera
            2. pertussis

Question 25

When AMP/ATP ratios go above 1, which enzyme can act to generate more energy? what are the types of activation for this enzyme? what disease manifests from its mutation?

Answer 25

glycogen phosphorylase

1. normal function of glycogen phosphorylase
   
   1. rate-limiting enzyme in glycogen degradation
      
      1. the enzyme is biologically active as dimer and requires pyrodoxal phosphate (B6) for its activity
      2. degrades glycogen to glucose 1-phosphate
2. activation
   
   1. allosterically
      
      1. ​amp
   2. posttranslational
      
      1. ​phosphorylation by glycogen phosphorylase kinase
         
         1. this kinase is turned on by cAMP dependent protein kinase A (PKA)

McArdles disease=glycogen storage disease

1. mutation in the muscle isoform of glycogen phosphorylase