What is the name of the substances that lowers the rate of reaction?

Explanation

Certain substances present in the cells may react with the enzyme and lower the rate of reaction. These substances are called inhibitors. It is of two types competitive and non-competitive inhibitors.

Competitive Inhibitor :
1. Molecules that resemble the shape of the substrate and may compete to occupy the active site of enzyme are known as competitive inhibitors.
2. Eg: The enzyme that catalyses the reaction between carbon di oxide and the `CO_(2)` acceptor molecule in photosynthesis, known as ribulose biphosphate carboxylase oxygenase (RUBISCO) is competitively inhibited by oxygen/carbon-di-oxide in the chloroplast. The competitive inhibitor is malonate for succinic dehydrogenase.
Non-competitive Inhibitors :
1. Certain inhibitors which may be unlike the substrate molecule but still combines with the enzyme.
2. This either blocks the attachment of the substrate to active site or change the shape so that it is unable to accept the substrate. Eg: The effect of the amino acids alanine on the enzyme pyruvate kinase in the final step of glycolysis.
(i) Certain non-reversible / irreversible inhibitors bind tightly and permanently to an enzyme and destroy its catalytic properties entirely. These could also be termed as poisons. Eg: Cyanide ions which blocks cytochrome oxidase in terminal oxidation in cell aerobic respiration.