Unformatted text preview: tion potential of Fe++ Ferredoxin- an electron carrier Note how enzymes resemble mineral surfaces, in a new matrix. Not all enzymes require
Enzymes R-groups can participate
in chemical reactions with the
substrate Enzymes can simply orient/bend
substrates R-groups’ charge can facilitate a
reaction Many of the minerals and cofactors critical for catalysis
may also be clues to how catalysis arose -Perhaps originally simple minerals were catalysts
Some cofactors may have been adaptors that enhance or
restrict this catalytic activity
Amino acids (and later proteins) could be new
developments that enhance speciﬁcity for particular
substrates. Without a catalystRate (v) is rate constant (k) x [S] = k[S] Enzymes add another step to the reaction:
S + E <-> ES <-> E + P
The substrate has to bind to the catalytic surface.
So the rate of a reaction can be limited by the availability of active
sites. (note this axis is not [P]!!!) Rather than S <-> P [S] (note this axis is not ;me!!!)
Note also, in these discussions we’ re talking about a specific experimental setup
We measure initial reaction rate in a reaction that has only substrate, not product. How would you measure dependence of reaction rate on [S]?
Add some enzyme to a little tube with a certain amount of S,
Measure how much product is made in 1st minute of the reaction
Toss the tube.
Try again with a little higher concentration of S. Why does the enzyme-catalyzed r x reach a maximum rate? Initial reaction rate Why does the catalyzed reac5on rate
ﬂa[en out at high [S]?
a) The back reac5on starts up
b) The reac5on can only go so fast
that’s the top speed
c) The enzyme is too busy to cope with addi5onal
substrate kf When [S] >> [E], the velocity
simply reflects the catalytic rate
of the enzymeincreasing substrate
concentration doesn’ t increase
velocity, because the
substrate’ s stuck waiting for an
available enzyme… Reaction without enzyme: S (substrate) -> P (product)
With a req...
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