Optimum catalse pH- help me out please.

[sonicscorch]

Hi guys. I'm an A Level Biology student in the UK, and I've just done an experiment to find the effect of pH on catalase. I used powdered catalase and expected the optimum pH to be 7, which I could have explained...

 

But it came out quite clearly as 10, and I have no idea why, as it contradicts the research I have done on catalase.

Can anyone explain this to me? Because I have to write it up and right now i'm completely stumped.

Cheers.

[John Cuthber]

How did you do the experiment?

[sonicscorch]

Here's my outline method:

• Fill 14 clean test tubes with 10ml of 10% hydrogen peroxide solution, using a small pipette and 100ml measuring cylinder.

• Leave one of the test tubes at neutral pH7, and check this using a digital pH meter. If the pH does not initially register at 7, then buffer solution should be added until the solution is completely neutral.

• Then, monitoring the pH with the pH meter, add either sulphuric acid or sodium hydroxide to each of the remaining test tubes, so that there is a hydrogen peroxide solution that is each pH ranging from pH1 to pH14.

• Add 5ml of catalase to the first test tube, and immediately attach a bung and gas syringe to the top of the test tube.

• Use a stopwatch to time the reaction for two minutes, before recording the amount of gas that has been produced and removing the gas syringe.

• This should then be repeated for the remaining 13 test tubes, until results for all 14 pHs have been recorded.

 

Cheers. Any information would be helpful.

[dttom]

would there be anything to do with the catalase and sulfuric acid or the sodium hydroxide? and I suggest to count the time needed to produce a certain amount of gas instead of fixing a time and count the volume of gas produced.

besides, how do you know catalase work best at pH10, from textbook or internet? has it claimed that it is in vitro or in vivo, such could matter.

[John Cuthber]

It may be a bit late to say this but did you measure the pH afterwards?

 

I think the catalase solution you used was buffered (possibly by accident due to impurities) to some pH a bit lower than its optimum. When you added this to the dilute NaOH solution that was your pH10 solution you changed the pH to nearer the optimum and got a faster reaction. With the other solutions there was either not enough NaOH to get to the optimum or so much as to drive the pH further from the best value on the alkaline side. Adding acid wouldn't help if the stuff was too acid to begin with.

 

What you need to do is repeat the experiment using buffer solutions to ensure that the pH stays (pretty nearly) the same when you mix the solutions.