Lead Inhibitor on Enzyme activity?

Question

I've been doing an experimental write-up for college on an experiment we did into the effects of lead nitrate as an inhibitor to catylase activity on hydrogen peroxide break-up.

One question I have to answer (for mucho extra credit) is what type of inhibitor is lead?

There may well be a very simple answer to this question but I cannot find it. Alternatively, it could be a very complicated answer!

Please help, I've looked everywhere!

Thanks

Pretty sure the lead nitrate sln is Pb (NO3)4. Does that make it non-competative or competative? Is it competative if the enzyme is denateured?

Okay, the results... The control was H2O, the concentrations of Pb (NO3)4 used were 0.0001M, 0.001M, 0.01M and 0.1M.

Teepol (detergent) was added to contain the O2 production and provide a way to measure. Max bubbles on H2O (predictably) and decreasing volume bubbles as we move up the concentrations.

I'm hazy on wether or not this means competative or non.......

Hope this makes things clearer.

Cheers

Answer 1

Depends on the experiment you did. Probably you should have enough experimental info to deduce the type of inhibitor.
There are plots that you can do with your data and by looking at the change in Km and Vmax you can tell what type of inhibitor it is.

[Edit] sweetandangry we are talking about Pb+2 so most probably it is a competitive inhibitor, substituting the ion in the catalytic center.

However you have to back this up experimentally (lower Km, same Vmax).

[Edit] Usually lead is Pb+2, but it can also be +4. That's not the point. You have to check your data. Denaturation is irreversible non-competitve inhibition but I don't think that it is the most plausible scenario unless you had a very high salt concentration and/or observed precipitation.Without more info we cannot say for sure.

[Edit] With these data you cannot say. In order to say what type of inhibitor you need to:
1) measure the rate of the reaction V as a function of substrate concentration [S] in the abscence of the inhibitor. From the 1/V vs 1/[S] plot (Lineweaver and Burk plot) you calculate the Vmax and Km
2) do the experiment that you did to find the order of magnitude of inhibitor concentration [I] that you need to use for a feasible range of [S] so that you don't have too strong or too weak inhibition.
3) Repeat experiment (1) in the presence of this moderate [I]. Calculate the new Vmax* and Km*.
If Vmax*=Vmax and Km* If Vmax* If Vmax* and a special case is un-competitive inhibition (the inhibitor acts by binding to the enzyme-substrate complex instead of the enzyme alone). Then again Vmax*

Answer 2

Beside the question of the type of the inhibition, I would like to mention something about the effect of metal cations on hydrogen peroxide itself.

The hydrogen peroxide bleaching of fibres in the production of CTMP (chemi-thermo mechanical pulp) in paper industry is strongly suffering on the inactivation of oxidative effect of H2O2 by metal cations (which must be chelated away before the bleaching reaction). I think that this should be taken into account when estimating the enzymatic activity on the basis of bubble production in your experiment.

The solution of your original problem about inhibition may be found if you check the effects of Pb+2 on both the chemical bonding behind the 3-dimensional structure of the enzyme and the catalytic site of the enzyme.

My chemical studies have taken place at 70' and both my poor memory and the lack of the recent knowledge about recent enzyme research prevent me to help you in a more detailled way, I'm sorry. Good luck, however, to find the answer!

Answer 3

there are a determination of inhibitors of polyphenoloxidase,mostly aggressive ones like alpha naphthol, or pyrogallol that are non-oxidizable pseudosubstrates. also sturdy antioxidants which contain nutrition C or quite glutathione at ~ 0.a million mM inhibit with the aid of as a lot as 80% or extra. The very powerful non-aggressive inhibitor 3,4 dichlorophenyl serine can shrink interest very nearly fullyyt at 0.05 mM .

Answer 4

i tried searching for you but i couldn't seem to get my head round it but i think it's a non- competitive inhibitor(or non- active site directed) because that normally involves metals doesn't it?but try typing in "lead as a non-competitive inhibitor" and see if that works..sorry for not being a great help!