Lec 15 - Regulation of Protein Function

alter substrate and product conc change enzyme confirmation via : Allosteric regulation Covalent modification Proteolytic cleavage

Up or Down regulation in protein synthesis change protein degregation rate

substrate concentration - less substrate lower enzyme activity Product inhibition - more product accumulation will inhibit the forward reaction eg - glucose 6 p inhibits hexokinase activity

allosteric ezymes show a sigmoidial curve between rate and conc T state - low affinity R state - high affinty allosteric binding causes a confrontational change think haemoglobin allosteric activators increase proportion of enzyme in R state allosteric inhibitors increase the proportion of enzyme in the T state back to gylcolysis notes : phosphofructokinase (PFK) - allosterically regulated activated by low energy AMP, fructose 2,6 biphosphate inhibited by high energy ATP citrate and H+

Phosphorylation via protein kinases transfer terminal phosphate from ATP to OH on ser,thr,tyr (amnio acids) protein phosophotases - catalyse dephosphorylation ie reverse reaction phosphorylation adds a bulky negative charge the created phosphoryl group can make H bonds this changes protein confirmation this allows for amplification effects - singal orders of magnitude larger within seconds (extra) we can alter rate of de/phosphorylation

the presence of glycogen will activate glycogen breakdown enzymes and at the same time turn of the glycogen synthase enzyme

proteolytic cleavage can activate enzymes this is good in digestive enzymes - synthesised as zymogens (inactive) in the pancreas and stomach - activated later once into the digestive tract - as we dont wanna dissolve our own cells !! extra : pepsinogen — acitvate —- pepsin blood clotting is mediated by a proteolytic cleavage cascade apoptosis works via proteolytic enzymes being activated

activation of most digestive emzymes are controlled by trypsinogen to trypsin once activated trypsin can cut many pro-enzymes into their active forms lipase, elastase, chymotrypsin, carboxy peptidase pancreatic trypsin inhibitor can bind tightly at active site to inhibit trypsin activity

Change the rate of protein synthesis - enzyme are made less or more by up/down regulation change the rate of protein degredation - ubiquitin-proteasome pathway

there are 13 clotting factors that form a cascade processes we have an intrinsic pathway - damaged endothelial lining of blood cell promotes binding of factor XII and an extrinsic pathway - trauma releases tissue factor III both these paths activate factor X (10) factor X activates prothrombin to thrombin leads to production of fibrin and formation of the fibirin clot it is an amplification cascade - allows for formation of a clot from very small amounts of initial factor lead to one pro enzyme being activated to an enzyme which converts a pro enzyme to an enzyme ect thrombin / fibrinogen presence activates earlier parts of the intrinsic pathway - positive feedback

serine protease - active enzyme area Gla (g-carboxyglutamate) resides domains target it to appropriate site for activatin - brings together clotting factors - COO- groups on gla find Ca2+ which is present at the break two kringle domains help keep prothrombin in the inacitve form - these are cut off to activate it this flash card is not that important

fibrinogen - crab protein Alpha and beta negative regions prevent aggregation thrombin cuts of negative alpha and beta regions fibrinogen now can ploymerize - forms the clot cross linking - amide bonds - help stabilise the clot thrombin acitvates another clotting factor to do this

-defect in factor 7 treat with recombinant factor 7

localisation of prothrombin - clotting factors are diluted by blood flow, disposed of in the liver digestion by proteases regulating the clotting process by specific inhibitors such as antithrombin inhibiting thrombin

fibrinolysis - uses proteolytic acitvation plasminogen (inactive) is acitvated to plasmin plasmin breaks down fibrin into fibrin fragments

• Inactive zymogens are present at low concs • proteolytic activation • amplification of intial singal by a cascade system • clustering of clotting factors at damage site • feedback activation by thrombin ensures the continuation of clotting • termination of clotting by multiple mechanisms • clot breakdown controlled proteolytic activation