Enzymes II Flashcards
What is Vmax?
Maximal velocity
All of active sites are filled
What is Km?
Michaelis constant
Substrate concentration where half the number of active sites are filled
What is perfect enzyme?
Is an enzyme where chemistry that it carries out in its active site is now so efficient that limiting step is finding the substrate. As soon it finds a substrate + binds the chemistry is very fast
Perfect enzymes are…..
Diffusion controlled
Is limited by diffusion step
What is K3/Kcat?
Is catalytic rate obtained from Vmax
Is turnover number
What is equation for Kcat?
Kcat= Vmax/[enz] total
Give an example of a perfect enzyme
What reaction does it catalyse?
Triosephosphate isomerase (TIM) It catalyse the conversion of dihydroxyacetone phosphate into glyceraldehyde 3-phosphate
What is protease?
Is an enzyme that hydrolyses peptide bonds
Don’t cleave very peptide bond as they have selectivity
Are therapeutic targets
What do serine proteases contain?
It has very reactive serine which contain a very reactive serine which contains a very reactive OH group
Give example of serine protease
Chymotrypsin and trypsin
What is catalytic triad?
Serine 195, Asp 103 + His 57
What is importance of catalytic triad?
It is important because it makes serine OH more electronegative
Where is catalytic triad found in?
All serine proteases
Describe the specificity of chymotrypsin?
It has specificity for aromatic groups Phe, Trp, Tyr so bonds will be cleaved by this enzyme because hydrophobic pocket
Describe the specificity of trypsin for specific side chain?
Only cleaves positively charged residue upstream, Arg, Lys. It reaches to -vely charged pocket
Describe the specificity of elastase for specific side chain?
Only cleaves peptide bonds if N terminal of cleaved bond is small side chain e.g. glycine => narrow pocket therefore only small side chains can fit
Enzymes in catalysed reaction
Enzyme doesn’t use water in the first step it uses serine to attack peptide bond
OH group can attack ketone group of peptide bond
Enzyme is splitting the bond, releasing part of polypeptide chain + links to other part of chain making an ester intermediate
Ester are easier to hydrolyse than amides
Ester intermediate (called acyl-enzyme) can react with water, releasing other part of polypeptide chain
Enzyme is regenerated, unchanged
What was discovered from structure of mitochondrion?
Inside inner membrane, it was loaded with lollipop (stick with round end)
Lollipop is made up of 2 very important components=> pore which is stuck into inner membrane which allows proteins to go through it, head of lollipop is rotary system which enables ATP to be made from ADP + Pi
Rotary ATP synthase has 3 active sites activated by rotating spindle
Proteins are fed through basal plate
Around rotor, there is hexagonal proteins => has a hole in middle in which rotor sits called stata
There are 3 active sites which bind ADP + Pi
As protons feed through, it turns around and ATP made
Energy of protons are used to make motor turn in order to make ATP
What is topoisomerase II?
A molecular clamp
Unlinks tangled chromosomes
Unlinks loops of chromosomes during mitosis to physically separate them
Describe the structure of topoisomerase II?
Dimeric structure =It is made up of different subunits + looks like a clamp
What drug is topoisomerase a target for?
Anti cancer drugs
