Noncompetitive and uncompetitive inhibition are two types of enzyme inhibition mechanisms. 

Noncompetitive inhibition 

• In noncompetitive inhibition, a chemical (enzyme inhibitor) binds to a site other than the enzyme’s active site. This changes the shape of the enzyme’s active site, which prevents the substrate from binding because it no longer shares affinity with the enzyme’s altered active site. 
• Non-competitive inhibition can occur in the presence or absence of the substrate as non-competitive inhibitors can bind equally well to the enzyme and enzyme–substrate complex. 

Uncompetitive inhibition

• In uncompetitive inhibition, a chemical (enzyme inhibitor) binds only to the substrate-enzyme complex. This is common in reactions where two or more substrates are involved
• The formation of an enzyme-substrate complex is essential for uncompetitive inhibition to occur as uncompetitive inhibitors bind only to the enzyme–substrate complex.