How much penicillinase is needed to deactivate 125mg of amoxicillin?

Penicillinase in penase concentrate from CPC. 20,000 Levy Units/ml/min

I need IU of 125 mg of amoxicillin.

Please note that the problem is with finding the right parameters for amoxicillin, not penicillin G.

My goal is to test an amoxicillin product (i.e. it contains more than just amoxicillin) so the overall problem is more complex, I wanted to keep the question focused.

I would like to know the minimal amount of penase needed to deactivate 125mg of amoxicillin (that's the amount of amoxicillin in the product) in a reasonable amount of time, say 5 minutes. I want the minimal amount of penase because I am not sure what is its influence on bacterial growth, I am going to test that separately. Maybe I am going wrong about the whole problem?

I think that this paper could be helpful in general: Microbiological Applications of the Inactivation of Antibiotics and Other Antimicrobial Agents but it's behind a paywall and I can't access it at the moment. So far, I failed to find any other useful resources.

  • 3
    $\begingroup$ This question cannot be answered without a time factor. Assuming no enzyme degradation, theoretically a single enzyme molecule can do it given enough time. $\endgroup$
    – March Ho
    Aug 12 '15 at 12:18
  • 3
    $\begingroup$ Well, you could be a chap and answer the question, instead of downvoting, including factoring in the time factor - it would be just one abstraction higher than a simple number and also more valuable and informative. $\endgroup$ Aug 12 '15 at 12:43
  • $\begingroup$ This is not a homework question! It even doesn't fit the homework policy. The first two points are off the table immediately. The last point, "A question that addresses a basic biology concept that may seem trivial to biology professionals" is obviously invalid too since it seems none of you are able to answer the question for amoxicillin as opposed to penicillin G. $\endgroup$ Aug 13 '15 at 7:33
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    $\begingroup$ @jkbkot You should also show some basic effort. Levy Unit is not a standard enzyme activity metric. As it seems it is used only in case of Penase. Add some of your calculation on how much penicillinase is would deactivate an equal amount of penicillin. From your question it seems you are asking others to do your calculation. The edit was useful but I suggest that you add some more details. $\endgroup$
    Aug 13 '15 at 8:18
  • $\begingroup$ @WYSIWYG I agree I should have added more details from the beginning, sorry about that. I'll add more of my own research a bit later in the day, thanks. $\endgroup$ Aug 13 '15 at 8:21

As March Ho has pointed out, we could do with a bit more information on this one.

I am going to attempt the calculation for penicillin G, and the necessary information seems to be available.

  1. From here, A Levy Unit (LU) is the amount of penicillinase that inactivates 593 IU (International Units) of Sodium Penicillin G per minute at 25°C and pH 7.0

  2. From here and here, the specific activity of penicillin G is about 1667 Units/mg

  3. I am assuming your concentrate is 20,000 Levy Units/ml (not 20,000 Levy Units/ml/min, which does not make sense to me)

  4. Therefore 1 Levy Unit will inactivate (593/1667)mg, or 0.356 mg, of penicillin G per minute, pH 7.0 and 25oC

  5. 2.81 Levy Units will inactivate 1 mg penicillin G under identical conditions

  6. 351 Units will theoretically inactivate 125 mg penicillin G in 1 min under the conditions stated.

  7. Your concentrate is 20000 Units/ml, or 20 Units per microliter. So you will need (351/20) microlitres, or about 17.5 ul.

  8. This assumes that the enzyme continues at a constant rate given by the specific activity right until the end. This might not necessarily be the case, as one would expect the rate to slow down as the substrate concentration falls below Km. Personally, I would use at least a 10-fold excess. 176ul - Seems a lot?

Please feel free to provide further information, or to edit the answer in any way you feel is necessary

  • $\begingroup$ Thanks for the answer! It helps me to realize that 1) I seem to understand how to compute this myself, I actually did it for penicillin G and got the same result as you 2) the real problem is that there seems to be no IU definition for amoxicillin, or at least I'm failing to find it so I'm not sure how much penase is needed. I am actually figuring out a way to test amoxicillin - maybe I could ask about that directly too? I need to double check pharmacopoeia first though... $\endgroup$ Aug 12 '15 at 20:58
  • $\begingroup$ Now I see they say that for other penicillins one should use 20 times more penase. Is there no more specific information available? $\endgroup$ Aug 12 '15 at 21:02

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