Re: Can lead act as a co-enzyme with lipase?

I would not expect either lead ions or nitrate ions to catalyze this reaction (though it’s always possible I’m wrong).  It’s hard to know for sure, but it sounds to me that something else may be going on here other than what you’re trying to measure.   The problem may be related to your method of measuring whether a reaction has taken place.  Measuring pH change is an accepted and time-honored method of measuring the hydrolysis of lipids, but since this is an indirect method it is important in every experiment to rule out any possibility that a pH change was caused by something else.  The pH change is caused by the release of fatty acids from the triglycerides that make up cooking oil, causing the pH to go down.  You very correctly looked at the pH of the lead nitrate solution, and report that it is neutral.  However, it is quite possible that the lead nitrate solution could cause a pH change in this mixture even though the lead nitrate solution itself is initially neutral.

You might do experiments to answer the following questions: 1. Does the pH change occur over a measurable time course, or is it instantaneous?  If you find the latter, I’d suspect something else is going on other than hydrolysis of the oil.
2. Can you observe a pH change when the cooking oil is omitted but everything else is left the same?  A positive answer would definitely point the finger at some reaction other than hydrolysis of the oil.
3. In the same vein, you might try different kinds of oil (e.g. corn, canola, peanut, sesame, olive).  Since they have different fatty acid compositions, they should exhibit different rates of hydrolysis.  (I know that will definitely be true for lipase-catalyzed hydrolysis)  If they all show the same rate with lead nitrate alone, again I’d suspect something other than hydrolysis of the oil.
4. Try other salts of lead: chloride, etc.

When a scientist observes an effect but the effect is the result of the experimental design and not real, we call this an artifact.  You may have an artifact here.  Beyond this, I can't think of anything else to explain your result.  If you would like to communicate with me further on this, please find my email address at the link below.

By the way, I hope you’re being real careful with the lead solution; I guess you know how toxic lead is.

David Reibstein, Ph.D. (Biochemistry)
Associate Dean, Albert Dorman Honors College, New Jersey Institute of Technology