Recall key properties of enzymes

Enzymes are biological catalysts. Their important characteristics are:

• They are mostly proteins.
• They lower the activation energy of biochemical reactions.
• Their activity depends on temperature and pH.
• They are generally highly specific for a particular substrate and reaction.

Evaluate each option

A: Enzymes are non-specific for a reaction and substrate.

• This is false.
• Enzymes are usually specific for both the substrate and the reaction they catalyze.
• Hence this statement is not true.

B: Almost all enzymes are proteins.

• This is true.
• Most enzymes are proteins, though a few RNA molecules can also act as catalysts.

C: Enzymes work as catalysts by lowering the activation energy of a biochemical reaction.

• This is true.
• This is the fundamental catalytic role of enzymes.

D: The action of enzymes is temperature and pH specific.

• This is true.
• Every enzyme has an optimum temperature and optimum pH.

Conclusion

The statement which is not true is: $\boxed{\text{A}}$

Comparison with stored correct answer

• Derived answer: $\text{A}$
• Stored correct answer: $\text{A}$
• They match.