When forming the following equation to determine the rate of enzyme activity what is the mg of protein?

 

 

Product Produced in mmol/time (min/sec etc)/mg of protein

 

Is it the amount of substrate used?

The sample? for example the amount of bacterial cells, though I'm not sure how you would determine its mass.

Usually when they refer to protein they mean the enzyme, but I do know that enzymes usually cannot be quantified in terms of mass?

 

Anyone know?

Enzymes are proteins, which have mass. Amount of protein in mg means the amount of enzyme in mg.

oK but then how do you calculate the mass of the enzymes if they are being produced by cells rather than inserted directly into the solution?

You would have to know how much the cells produce and derive the amount (in whatever unit) of enzyme that pertain to a given activity. The cell number will generally be insufficient. Enzyme kinetics (not velocity, with exception of motor proteins enzymes are not running around) is therefore normally only measured in in vitro assays. You can approximate those values, but it usually requires a lot of assumptions that are likely not true (i.e. quasi-steady state of enzyme production, relative constant synthesis and degradation rates, constant activity within cellular systems etc).

You can approximate those values, but it usually requires a lot of assumptions that are likely not true (i.e. quasi-steady state of enzyme production, relative constant synthesis and degradation rates, constant activity within cellular systems etc).

 

If only some of those assumptions extended to the en vivo world...biology and biochem might actually be comprehensible .