What causes competitive inhibition?
Competitive inhibition is caused by a reversible inhibitor(competitive one) which is selected by binding site of enzyme but can't activate the catalytic site.
Sometime a compound has the same structure to that of a normal substrate and fits at the binding portion of the active site. Thus in this way the enzyme can't be available to a normal substrate.
So, due to structural similarity with a normal substrate, a competitive inhibitor is selected by the binding site but is not able to activate the catalytic site. As it occupies the binding site, the binding site remains unavailable for a normal substrate. So, there is not any kind of product formation. This is known as competitive inhibition.
Malonic acid has structural similarity with succinic acid. Succinic acid is specific substrate for succinic dehydrogenase(enzyme). But in some cases, malonic acid fits in binding site of succinic dehydrogenase as a competitive inhibitor but is not able to activate the catalytic site so products are not formed.
Active site is divided into two sites:
Binding site : This site holds proper substrate and fits it as enzyme-substrate or ES complex.
Catalytic site : This part of active site transforms the substrate into products which means it is vital for catalytic activity of enzyme.
Hope it helps...