MadSci Network: Biochemistry

Re: How does conc. of Hydrogen Peroxide affect the IMMOBILIZED enzyme catalase?

Date: Tue Mar 28 01:41:43 2000
Posted By: Ewen McLaughlin, Lecturer, Chemistry, Swansea College
Area of science: Biochemistry
ID: 954161916.Bc

It's difficult to say what results you 'should' get without knowing your exact methods. Anyway, I'm always wary of saying that results are 'wrong' because in science results are always right; theories and experiments are wrong!

I'm not sure how active the immobilised enzyme will be. Depending on its exact relation to the surrounding alginate the active site could be quite unaffected or totally out of commission.

What I think you've found is the maximum rate of reaction, which is given by k(cat) times the enzyme concentration. k(cat) is the rate of formation of product from the enzyme substrate complex in simple Michaelis-Menten kinetics. I'd predict from this that the rate will be directly proportional to the enzyme concentration, particularly if you reduce the enzyme concentration.

Basically, this is zero order with respect to peroxide; as you said. Remember that zero order is untrue! Zero order says that changing the peroxide concentration has no effect on reaction rate, but this is only true at high peroxide concentrations. I'd be very surprised if the reaction proceeded at the same rate if you reduced the peroxide concentration to nothing!

At low concentrations, Michaelis-Menten kinetics predict that the rate will become first order for the substrate (peroxide). The beauty of the maths is that it allows zero order kinetics at high concentrations but first order kinetics at low concentrations.

I'm looking at p99 et seq of Fersht's book, Enzyme Structure and Mechanism (2nd edition, 1985, WH Freeman). p118 gives the useful shortcut of transit times.

Another text with the details of these kinetics is the ubiquitous Stryer ('Biochemistry' 4th ed 1995 Freeman, pp192-5)

Ewen McLaughlin, PhD (Cantab) (failed!)

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