Effect of changing pH of pepsin on hydrolysis

[petey]

Hi,

Did my A2 biology coursework. I compared the rate of hydrolysis between pepsin 2.8 and 7.0 using milk protein. Pepsin works in the stomach, so should have a faster hydrolysis rate in the acidic pH value. But when I measured transmission percentage I got a mean of 9% for 2.8 and 15 for 7.0 pH. My teacher had no answer, and suggested flipping the results, but I think this is dishonest and feels wrong. What reason/s could there be for this anomaly?

Many thanks,

 

[chemisttree]

What chromophore were you measuring? Did you measure the transmission percentage at pH 2.8 and compare it to the transmission percentage measured at pH 7? Could the extinction coefficient of the chromophore have a different value at those two pH's? Was the milk protein solution cloudy at one pH and clear at another?

 

[epenguin]

Did my A2 biology coursework. I compared the rate of hydrolysis between pepsin 2.8 and 7.0 using milk protein. Pepsin works in the stomach, so should have a faster hydrolysis rate in the acidic pH value. But when I measured transmission percentage I got a mean of 9% for 2.8 and 15 for 7.0 pH. My teacher had no answer, and suggested flipping the results, but I think this is dishonest and feels wrong. What reason/s could there be for this anomaly?

Many thanks,

Good, shows you have scientific mentality. What is the point of experiments if you force and falsify results?
Experiments do not always come out as they 'should', especially if you do not have time to find out why.
What was the buffer?

 

[Moonbear]

What chromophore were you measuring? Did you measure the transmission percentage at pH 2.8 and compare it to the transmission percentage measured at pH 7? Could the extinction coefficient of the chromophore have a different value at those two pH's? Was the milk protein solution cloudy at one pH and clear at another?

Indeed, this has come up with other similar kinds of experiments. What indicator is being used and what does an increase in transmission actually mean in terms of that indicator?

Good, shows you have scientific mentality. What is the point of experiments if you force and falsify results?
Experiments do not always come out as they 'should', especially if you do not have time to find out why.
What was the buffer?

Great point too! It is unfortunate for a teacher to simply recommend switching the results. Though, I will point out that from an educational perspective (rather than a truly experimental one), I've had days when equipment was malfunctioning or reagents were improperly prepared and nobody got the results they should have gotten for an "experiment" that should have a known outcome...in those cases, I've provided data to the class to use in preparation of their reports that was different from what they obtained, but that was recognizing they did the best they could and something known to me but not them had gone wrong. Under ideal circumstances, they'd have repeated the experiment and checked for such malfunctions, but limited class time is rarely an ideal circumstance.

So, on one hand, it is good to consider if there is an explanation for seemingly contradictory results relative to predictions, and on the other hand, the teacher may be aware of something that went awry and it would be better from a pedagogic perspective to simply do as the teacher recommended and switch the values (maybe s/he realized afterward that two reagents were switched, for example).

 

[Borek]

My teacher had no answer, and suggested flipping the results,

Perhaps my English fails me, but it sounds a little bit ambiguous to me. Were you suggested to flip the results (i.e. falsify your data), or were you suggested that some experimental error could lead to flipping samples/results (i.e. data is already wrong)?

Borek

 

[epenguin]

Yes e.g. solutions or labels could get switched.

I have just though, were solutions made much before? Could the pepsin have worked on itself? Does it?