Lock & Key: Maltase's active site has a specific shape complementary only to maltose. Sucrose and lactose cannot fit and bounce off.
Catalysis: Maltose binds → enzyme-substrate complex forms → maltose is hydrolysed into 2 glucose molecules → enzyme is released unchanged.
Denaturation: Above 35°C or outside pH 6.5–7.5, the enzyme's shape changes. The active site distorts so maltose can no longer fit.