Activation By Cleavage

Question 1

Availability of substrate or cofacter is important for reactions that function near equillibirum

Answer 1

for enz= lac DH

equilibrium shifts towrds lactate in anerobic muscle tissue

equilibrium shifts towards pyrvate in the liver tissue

Question 2

The role of non-enzyme catalyzed reactions on rate

Answer 2

not reagulated, and cant be controlled but can determine the flux through a pathway

as is the case for and anomerization reaction between aFBP and bFBP

the anomerization reaction probaably does not limit glycolysis, but may limit glyconeogenesis

Question 3

Product inhibition

Answer 3

ex hexokinase

product of the reaction can be an allosteric effector of an enzyme, so there exists sperate binding sites for the products in additon to the active site

competitive inhibiton

product can techinically bind to the active site in a reversible process, however this is a sloppy process of regulation.

because you dont really want product to build up to high enough levels where this would be functional

Question 4

Activaiton by cleavage

Answer 4

many proteases are synthesized in an inactive form (proenz or zymogens)

they are activated though the action of other proteases (a peptide is usually removed in order to activate the enzyme)

this is an irreversible process

Question 5

general features of activation by cleavage

Answer 5

activation can occur outside the cell

activation does not require ATP

aequence provides a rapid, amplified response to a small initial signal

system generally requires safeguards to prevent premature activation (since the activation is amplified)

May need some wat to turn of the system (other than waiting for enzyme degredation)

Question 6

What reaction does enteropeptidase catalyze

Answer 6

trypsinogen to trypsin, ONLY in the intestine

cleaves on the C-term of positive residues, hydrophillic Asp 4x peptide leaves (this region keeps the meta-stable loop in contace with water)

cleavage of the loop causes the hydrophobic Ile-val residue to move inwards and form the proper active site of trypsin

salt bride stabalizes (ile 16 and asp194)

glycine NH on backbone forms the oxyanion hole

tryspin is now autocatalytic and can do the reaction in addition to enteriopeptidase

Question 7

Protection of the pancrease

Answer 7

this aint a serpin boi

need this because even with out activation teh active site is partially formed, and thus could still in theory get tryp tryp cleavage

thus, premature activation of the proteolytic cascade could be catastrophic

protection is afforded in two ways

1) zymopgens are stored in seperate organs from activating enteropeptidase
2) there exists pancreatic trypsin inhibitor in the pancrease which deactivates active trypsin in the pancrease. This is a super strong competitive inhibitor that fits 100% complemetry. Lock-and-key, does not ever unbind (even tho it could the enz gets ubiq and degraded first)

Question 8

elastase

Answer 8

two types

digestive and neutrophil

pancreatic elastase is similar to the trypsin bois

neutrophil elastase is for the breakdown of collagen, and is inhibited by a serpin, unlike the pancreatic version

Question 9

a-1 protease inhibitor

Answer 9

orignally called anti-trypsin (only inhibits in vitro)\

actual purpose in vivo is to inhibit neutrophile elastase

is a serpin

Question 10

elastase is inhibited by a-1 protease inhib

Answer 10

elastase will cleave at the C terminal of a small hydrophobic AA res is Methionine

there exists a met ‘trap’ on the a-1 inhib, when met is grabbed by the elastin, the loop is cleaved on a-1, and it pulls and deforms the elastse active site

a very fancy suicide substrate

Question 11

tobbaco smoke and anti elastase

Answer 11

the methionine is oxidised to metionine sulphoxide and no loger can act as bait

elactase can now attack lungs and cause harm :(

Question 12

activation of factor X

Answer 12

two routes

Intrinsic pathway (contact system)
-> all porotien componetns are contained in the blood, and ultimately results in the VIIIa-IXa complex which can activate factor X

Extrinsic pathway

• > one of the components here arises from damaged tissue = tissue factor
• > reuslts in the TF-VIIa complex whihc can activate Factor X and factor IX

Question 13

Activaiton of prothrombrin

Answer 13

Prothrombin is cleaved by prothrombinase (factor Xa) twice

• > one cleavage releases N-terminal propeptide
• > one cleavage separates teh A and B chains freeing ile321 as the new N terminus. This allows the new pair of ile321 and asp524 to form

cleaves at the gla domains these Gla domains chelate calciuma and bind it to the exposed inner leaflet (PL= phospohatidylserine and phosphatidic acid)

this is then cleaved by activated thrombin to form active thronbin