Question

Which of the following is not an example of absolute substrate specificity?

(a) Glucose to glucose-6-phosphate by glucokinase

(b) Hexokinase phosphorylating one or more kind of hexoses

(c) Lactose to glucose and galactose by lactase

(d) Urea to ammonia by urease

I have been asked this question in quiz.

Origin of the question is Specificity of Enzyme Action in section Enzymes of Enzyme Technology

Answer 1

The correct answer is (b) Hexokinase phosphorylating one or more kind of hexoses

To explain I would say: The specificity in which the enzymes will act on the only substrate and catalyze only one reaction is referred to as absolute substrate specificity. Examples for such type of specificity are as follows:

• Glucose to glucose-6-phosphate by glucokinase

• Lactose to glucose and galactose by lactase

• Urea to ammonia by urease

Hexokinase phosphorylating one or more kind of hexoses is an example for broad substrate specificity, which means the enzyme acting on more than one structurally related substrates.