Control of Metabolism Flashcards
how is the atp pool buffered during intense exercise
by PCr
powering muscle contraction with glucose
- ATP from glycolysis
- intense exercise - PCr buffers ATP pool (though PCr is limited so must also mobilise glycogen
- anaerobic metabolism producing lactate - possible for short periods only
- prolonged exercise - aerobic metabolism of glucose, producing ATP more slowly, by OXPHOS
liver and blood glucose
- after a meal - insulin stimulates uptake of glucose, which is converted to glycogen, FAs, used as fuel
- after a fast - glucagon stimulates glycogenolysis, glucose release, mobilisation of FAs from adipose
3 key control points of glycolysis
hexokinase, PFK1, pyruvate kinase - irreversible steps with larger changes in gibbs free energy
what happens to lactate and alanine from anaerobic metabolism in muscle
released into blood and converted into glucose in the liver - glucose then released into blood and transported to muscle
= the cori cycle
6 ways to control enzyme activity
- substrate level control
- cooperativity
- allosteric regulation
- covalent modification
- substrate cycling
- control through changes in enzyme concentration
substrate level control
when most useful?
- enzyme has greatest sensitivity to changes in [S] when [S}
example of substrate level control
glucokinase - an isoform of hexokinase with a high Km for glucose
- B cell - glucokinase is glucose sensor, increase glycolytic flux and insulin release
- liver - glucose uptake
cooperativity definition
binding of first substrate affects binding of subsequent
increases sensitivity
concerted model of cooperativity
binding of first substrate shifts equilibrium in favour of relaxed form which has higher affinity for further substrate
sequential model of cooperativity
binding of first substrate causes conformational change from T to R (higher aff), this causes second subunit to change from T to R, facilitates binding of 2nd substrate
hill coefficient
protein p with n binding sites for ligand L
n=hill coefficient, a measure of cooperativity (< no binding sites)
(read eqn)
allosteric effectors
bind to a site on the enzyme other than the substrate binding site and regulate enzyme activity
eg activator could produce a conformational change to stabilise the R state
allosteric effectors in muscle glycolysis
- G6P allosterically inhibits muscle hexokinase
- PFK1 allosterically inhibited by ATP and activated by AMP
- PK allosterically activated by F16BP
sensitivity of … substrate level control, cooperativity, allostery
substrate level = linear response
others are more sensitive, sigmoidal rather than hyperbolic response curves
substrate cycling example
F6P, F16BP, via PFK1 and F16BPase
AMP allosterically activates PFK and inhibits F16BPase, allowing massive changes in flux with small changes in AMP levels/ the enzyme activities
- payed for by ATP, energy released as heat
types of covalent modification
phosphorylation
acetylation
shape of curve with cooperativity
sigmoidal
example of cooperativity in a monomeric enzyme
glucokinase = monomeric with 1 glucose binding site. has 2 slowly interconverting forms
- at low S, the low affinity E’ form dominates
- at high S, the high affinity E form dominates
this gives a sigmoidal saturation curve
AMP changes during exercise and allostery
- large increase in AMP during exercise as 2ADP==>ATP+AMP by adenylate kinase
- PFK1 activated by AMP, increases F16BP steady state
- increases allosteric act of PK
- decrease in steady state G6P, less inhibition of hexokinase
so a coordinated increase in activities of these enzymes
protein phosphorylation
- at OH groups of ser, thy, tyr
- introduces neg charge so can cause large conformational change
- by kinases, removed by phosphatases
these enzymes are promiscuous - have many targets. also many regulatory subunits
enzymes of glycogen metabolism
glycogen synthase converts UDPG to glycogen
phosphorylase converts glycogen to G1P, which is in equilibrium with G6P
how is gluconeogenesis like the reverse of glycolysis?
most of the reactions are at equilibrium so readily reversible for gluconeogenesis
- the HK, PFK1 and PK reactions are not (these ones use ATP) so different enzymes are required for the reversal:
F16BPase and pyruvate carboxylase+phosphoenolpyruvate carboxykinase
glycogen synthase and phosphorylase activities
don’t want simultaneous activity as will just turn over ATP