The correct option is C Isoenzymes
Some enzymes have several molecular forms, example : 16 for α-amylase and 5 for lactate dehydrogenase (LDH). They are called as isoenzymes or isozymes. They differ in substrate affinity, maximum activity and regulatory properties. At biochemical level these enzymes are composed of different subunits. The different arrangement of subunits gives rise to differences in their biochemical activity.