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1. MSCDFSM BIOCHEMISTRY
ENZYMES AND COENZYMES II

2. ENZYME KINETICS: the rate at which an enzyme work is called enzyme kinetics. L.michaelis and
M..menten said that enzyme combines with substrate to form ES complex and that frequently break
doewn to form Enzyme and Product .and these reactions were assumed to be reversible reaction .
E +S ES ES E+P
Enzyme kinetics is a function of concentration of substrate available to enzyme .we have potted the graph
to study kinetics .substrate concentration is plotted at x and enzyme velocity is potted at y axis.and
hyperbolic curve is obtained .
M,N,O are the stages of reaction.when the substrate concentration is very low it represent as M ,when
the enzyme velocity reaches maximum it is represented by O and when the activity is haf of the
maximum ,it is represented by N .The rate of reaction is directly propotion to substrate concentration.
vmax
vmax /2

3. The michaelis – menten equation is : v=vmax *[s]
km +[s]
Where v = velocity
Vmax- maximum velocity
Km – Michealis menton constant expressed at moles per litre.
Km represents the substrate concentrate at which the velocity of the reaction is half of vmax
Km is an inverse measure of affinity or strength of binding between enzyme and substrate .the lower the
km the greater the affinity .
Point M : at this stage ,the substrate concentration is less than Km .and if substrate concentrate increase
its value does not change .and [s] can be ignored at denominator .
V=vmax*[s]
km
Point N : at this point ,substrate concentration is equal to michealis menten constant ,Km so the equation
becomes : v=vmax *[s]
[s] +[s]
v= Vmax *[s]
2[s]
v= Vmax
2
Point O : At this point , the substrate concentration is much higher than in comparison to Km so that Km
may be ignored .

4. V= V max *[s]
[S]
V=Vmax
Lineweaver Burk equation
to plot data conveniently , michealis menten equation is transformed to lineweaver equation .
1
V
This is lineweaver buk equation .

5. Km is not a fixed vaue and vary withstructure of substrate ,ph and temperature etc .
Factors affecting enzyme activity :
1. Concentration of enzyme
2. Concentration of substrate
3. temperature
4 .PH
5 .Activators
6 .Oxidation
1. Concentration of enzyme :
Increase in concentration will increase the catalytic reaction .because more catalytic sites are available to
perform reactions .
Enzyme activity
Enzyme concentration
2.Concentration of substrate :
When substrate is low in quantity ,the rate of enzyme is ow because all catalytic sites are not occupied by
substrate molecule so when the substrate will increase it will automatically increase the activity of enzyme .it
reaches a maximum point and then become constant .

6. 3. TEMPERATURE :
The rise in temperature acceerates the rate of enzyme catalyzed reactions upto certain temperature
called optimum tempertature.if the temperature is higher than the maximum temperature ,enzyme
become denaturated .for human beings it is 37degrees and for pants it is 60 degrees.
point A- optimum temperature.
4. PH :
Every enzyme has optimum PH .PH activity is due to their ionic nature .within narrow PH change the
changes are reversible but if PH is too high or too ow it becomes denatured.most of enzyme ranges
between 5 to 8 .pepsin and trypsin are active in high acidic medium 1.5 and high alkaline 8 medium .
ENZYME ACTIVITY
PH
5. ACTIVATOR
Activators are certain ion that influence enzyme activity .enzymes such as hexokinase require ATP ASO
NEED MG+2 IONS without these ions they become inactive .

7. OXIDATION :
Some enzymes having sulfhydryl group are very sensitive to oxidation .die to oxidation of –sh group by
aerial oxygen a disulfide linkage is formed .with a loss of enzyme activity that can be further restored by
reduction of enzyme by cysteine and glutathione etc
ENZYME INHIBITION
There are 3 major classes of enzyme inhibition :
1. Competitive inhibition
2. Non competitive inhibition
3. Uncompetitive inhibition
Competitive Inhibition :
This inhibition takes pace when a compound having strong structural resemblance with substrate
compete for catalytic site one the compound bind to site it enzyme cannot compete its actionbut if the
concentration of substrate is increased it will again activation of the activity and products wil be
formed.so this is reversible in nature
Eg. Succinate dehydrogenasein citric acid cycle succinate gets converted to fumarate and compound
malonate acts as inhibitor and if added to reaction , it reduces the product formation
Non Competitive Inhibition:
The inhibitor bind to the site other than catalytic site hence there is no competition between the two .it
cannot be reversed eg . Enzymes with –SH group are inhibited by metals like mercury and copper

8. Uncompetitive Inhibition:
Here the inhibitor binds with ES complex making it inactive .due to this it is difficult to make products .it
is very rare