Enzyme kinetics -what's the difference between an enzyme's "specific activity" and "catalytic efficiency"?

Question

I hope someone can answer this in layman's terms.

What do you mean by specific activity and how is it different from catalytic efficiency?

Answer 1

First of all what is activity?
Enzymes are catalysts. If you add a certain amount of an enzyme in a test tube with the appropriate substrate and the appropriate conditions then a reaction will take place with the catalytic help of the enzyme. In order to quantify this action we introduce the term activity.

There are different definitions for the term enzyme unit but we can generally say that 1 unit of enzyme is the quantity of enzyme that catalyzes the reaction of 1 micromol substrate per unit of time (e.g. min).

So going back to our test tube, if we added 100 mg of enzyme and those catalysed the reaction of 10 micromoles substrate per min then we would have 10 units in our test tube.
Specific activity is a kind of purity and concentration expression. It shows you how many units of enzyme you have per mg or microgram of total protein. In our case we would have 10/100 = 0.1unit/mg. Remember that enzymes are proteins and thus they are isolated by purification frorm living organisms. Thus they need to be separated from other proteins. This means that at the different steps of purification you will have varying specific activities which should be increasing as purification procedes (you start with a lot of proteins which don't participate in the reaction and as you are removing them with the purification the total protein corresponds more and more to just your enzyme). If you manage to achieve 100% purity with all of the enzyme in its active form, you will have a certain maximum value for the specific activity.However, in practice, since enzymes are proteins some of the enzyme might denature due to the purification and/or with time, thus the specific activity will drop.

Catalytic efficiency reflects the value of kcat and how many molecules of substrate can be processed by one molecule of enzyme in one unit of time (e.g. sec, min). It is a property of the enzyme molecule whereas specific activity is a property of our enzyme preparation/solution which becomes a property of the molecule only for 100% pure (no other type of protein present) and 100% active (none of the enzyme has denatured) enzyme.

Answer 2

Catalytic Efficiency Units

Answer 3

Replace "i.e." with "in other words" and "e.g." with "for example" and you'll understand the meanings, and never confuse them again!

Answer 4

hope you find good information at this site
http://www.bookrags.com/wiki/List_of_enzymes