ENZYMES WORK BY INDUCED FIT
The reason a particular enzyme will combine only with one kind of substrate is that the fit between the two is very precise. In fact, the fit is so precise, the combining of the enzyme and substrate results in a slight change in the shape of both. This precise fit that modifies both original molecules is called an induced fit. This "strained" fit acts to break old chemical bonds and form new ones, resulting in the formation of the product from the substrate. Once this change has occurred, the product is released from the enzyme, and the enzyme can combine with another molecule of substrate.