Question

What are different classes of enzymes? Explain any two with the type of reaction they catalyse.

Answer 1

Enzymes are divided into 6 classes each with 4 – 13 subclasses and named accordingly by a four-digit number.

Oxidoreductases/dehydrogenases: Enzymes which catalyse oxidoreduction between two substrates S and S’. E.g.,

S reduced + S’ reduced `→`  S oxidised + S’ oxidised

Transferases: Enzymes catalysing a transfer of a group. G (other than hydrogen) between a pair of substrate S and S’, e.g.,

S – G + S’ `→` S + S' – G

Hydrolases: Enzymes catalysing the hydrolysis of ester, ether, peptide, glycosidic, C – C. C-halide or P – N bonds.

Lyases: Enzymes that catalyse the removal of groups from substrates by mechanisms other than hydrolysis leaving double bonds.

\[\begin{array}{cc}
\ce{X}\phantom{...}\ce{Y}\phantom{....................}\\
\phantom{.}|\phantom{....}|\phantom{.....................}\\
\ce{C - C -> X - Y + C = C}
\end{array}\]

Isomerases: Includes all enzymes catalysing inter-conversion of optical, geometric or positional isomers.

Ligases: Enzymes catalysing the linking together of 2 compounds, e.g., enzymes which catalyse the joining of C – O, C – S, C – N, P – O etc. bonds.