An α-anomer is formed if in the interacting —CHO group —H is on the left and —OH is on the right; if —OH is on the left and —H is on the right, it is said to be a β-anomer (see Figure 2.6). Enzymes are very specific in their reactions with different configurations. For example, cellulose having a β(1 → 4) linkage cannot be hydrolysed by amylase, which can catalyse only α(1 → 4) linkages. Hemiketal rings are formed by the reaction of the aldehyde and ketone groups with the alcohol group of the same sugar.