Science Buddies: "Ask an Expert"

I was wondering if my project ideas 1) sounds like a good idea, 2) is at the level of a high school student, and 3) is original. I still need to do some more research regarding the specifics of the project, but this is the basic idea.

I was planning to do research on how different foods affect the antimicrobial properties of a humans salivary peroxidase system. The system works in that the thiocynate ion (SCN-) from saliva is oxidized by hydrogen peroxide (H2O2) which is given off as a waste product from bacteria in the oral cavity. This oxidization produces the hypothiocyanite ion (OSCN-) which creates the system. So for my experiment I was planning on having human subjects eat different fruits and vegetables with varying amounts if hydrogen peroxide and thiocyanate and then see if that will increase the peroxidase activity in their saliva. To test the saliva I will centrifuge it at 12,000 X g at 4 degrees celcius to purify it, and then I will test the peroxidase activity using spectophotometry. To the purified saliva, I will add potassium iodide because the iodide will oxidize the thiocyanate. The higher the oxygen concentration the higher the absorbence, thus I will be able to determine the relative increase in peroxidase activity through spectophotometry.

Thanks, Lizz

Hi Lizz,
It's great that you're thinking about potential ideas for your project. However, I am a little concerned about whether or not it will okay with judges and science fair guidelines that you give human subjects thiocyanate and hydrogen peroxide. There are various rules on this at different fairs, so definitely check with the rules before you go ahead of this. Working with human subjects will also force you to undergo more stringent paperwork and consent than working with other vertebrates, so just keep that in mind. In any case, keep researching, it sounds great!

Staryl13,
Thank you for replying. Regarding the hydrogen peroxide and the thiocyanate, I am not actually having the people consume the various chemicals, instead; I am having them eat foods such as bananas which studies have shown have slightly higher (naturally occurring) amounts of thiocyanate than other fruits. So I believe that my science fair will be okay with that.
Lizz

Hi Lizz,

I agree with your response that the science fair would most likely be ok with the study. Of course, you would still have to fill out IRB forms for including human subjects as part of your study, but since it doesn't seem dangerous, your project would definitely be approved.

In response to your original question, it seems like a very original project that is definitely at the high school level.

Now, if you wanted to really take it up a level, it would be wise to consider the kinetics of the reactions that are taking place. Most likely I'm guessing that the reaction looks like:
SCN- + H2O2 <--> OSCN- + H2O, so we could define rate = k(fwd)[SCN-][H2O2] - k(rev)[OSCN-], where k(fwd) and k(rev) are rate constants.

But, there is also an enzyme involved, so:
SCN- + H2O2 + SP <--> SP-SCN-H2O2 --> SP + OSCN- + H2O, where SP = salivary peroxidase.
I would advise you to search for some more papers to determine what the kinetics look like. In many cases with enzymes, the reaction follows Michaelis-Menten kinetics (http://en.wikipedia.org/wiki/Michaelis% ... n_kinetics). So, when you measure SP activity, it will depend on the rate of reaction, which, if it follows Michaelis-Menten or some other kinetics, will allow you to predict and determine SCN- and H2O2 concentration.

Hope this helps!
Aaron