Re: What does quotient ten mean when referring to the rate of enzyme activity.

Tom,

In an equation, a quotient is the number you get by dividing one number by 
another. For example, 36 divided by 12 = 3, so the quotient is 3. So a 
quotient of 10 refers to a tenfold change in the rate of enzyme activity. 

I would guess that the question about calculating the quotient ten 
experimentally refers to finding how much you have to increase the enzyme's 
substrate concentration in order to get a 10 fold increase in the rate of 
product formation. Usually, these type of measurements are made using a 
spectrophotometer that can detect the formation of product (or depletion of 
substrate) by it's light absorbance. For instance, the activity of lactate 
dehydrogenase can be measured by following the oxidation of NADH at a 
wavelength of 340nm. 

  Pyruvate + NADH <-> lactate + NAD

NADH absorbs light at this wavelength, but NAD does not, so the rate of 
change of absorbance at 340nm allows you to determine the rate at which the 
enzyme is working. By setting up a series of assays where the concentration 
of pyruvate is systematically varied from low to high concentration, and 
measuring the initial rates of NADH oxidation will allow you to see how the 
rate of turnover of the enzyme is affected by the substrate (pyruvate) 
concentration.