[scientizscht (OP)]

Hello!

I know for an enzyme the below as well as the stoichiometry of the reaction:
1) KM Value
2) Turnover Number
3) kcat/KM Value

I need to know how much substrate will be converted per minute for a given substrate concentration.

Which is the right value/number to use and how?

Thanks!

[Eternal Student]

Hi.

   This looks suspiciously like a homework question or something similar.   I'm not sure what, if any, recommendations apply on this forum but it seems prudent not to deprive an individual of the opportunity to learn something by trying the work themselves.    Typically some guidance or assistance is provided rather than a complete solution.
    If  you have no idea where to start then it would be reasonable to suggest you look up  Enzyme Kinetics  and especially the following things:

1.   The Michaelis-Menten equation for enzyme kinetics is your main "way in".    Depending on how complicated your stoichiometry is, this equation and its derivation might only be a blueprint or indication of what you need, conversely if your situation is simple, it's exactly what you need.
2.   Basic definitions of the quantities  K_m   and   K_cat = "turnover number"  that you have mentioned.  These are things you can substitute into the equation above to get everything in terms of quantities you know.

    A minor complication for your problem is getting things in the right units.   Usually everything is in moles per second and you seem to want a reaction rate per minute.   That's minor and easily sorted.
   Another minor note:   You haven't mentioned that you know the enzyme concentration but you will require that information or else it will remain in your final expression for the reaction velocity.   It appears in the basic definition of K_cat that you will use and substitute into the Micehaelis-Menten equation.   There's no clever algebraic trick you can do to eliminate that variable.   We know that the reaction rate will increase if we increase the enzyme concentration, so we know this concentration affects the final answer.   We also know that the enzyme concentration can be changed without affecting the quantities  K_m , K_cat or the stoichiometric values  that you have been given, so it is an independent variable (you can't obtain it from the information you have).   Unless you have more information, then the enzyme concentration will appear in your final answer.

   A bigger complication is that you have suggested the stoichiometry of the reaction may be unusual.   The basic situation is   1 molecule of enzyme picks up 1 molecule of substrate,  1  enzyme-substrate complex is produced and  finally there is 1 molecule of product with the free enzyme released.
E   +  S    →    E-S     →   E  + P
   A simple modification of this would be to have an enzyme with two active sites,  each capable of acting independently to produce product.   That's a minor modification to the general theory, where you can simplify the situation and effectively consider the concentration of active sites instead of the concentration of the enzyme molecule  (one is just double the other).
     However, there can be more complicated situations with enzymes that require two (or more) different substrates and will only work to catalyse a change when both (or all, or certain combinations of) sites have been bound.   Knowing the overall stoichiometry of the reaction is not enough, you need to identify the rate limiting process and have information for that.

Best Wishes.

[scientizscht (OP)]

Thanks, it is indeed homework-like but I am not in format education anymore.

I am just looking for the equations or one of these nice online calculators if they exist.

The challenge I face are:
1) choose the right property
2) find the right equation as I mostly find definition equations (ok I suppose that is a starting point)
3) navigate the definition restrictions (e.g. kcat/KM seems to work only in specific relative concentrations)
4) as you pointed, find the right units because I need absolute conversion rates e.g. moles per minute or grams per minute and not something relative (at least without knowing how to link it)

The stoichiometry is first order, ie. one substrate converted by one enzyme to give one product (and another one but ok). Now if this happens in one step or multiple is something I don't know but I can bare that approximation.

[Eternal Student]

Hi again.

   How are you getting on then?  You can always write more if required.

I am not in format education anymore.

     OK.   I don't know what that means.  You could be self-educating or learning new stuff just for fun and personal interest.   That seems reasonable and commendable.

Best Wishes.