The induced fit hypothesis was proposed by Daniel Koshland in 1958. It is a modified version of the lock and key hypothesis that better matches evidence about the structure of enzymes.In this model:
• the active site is flexible, not rigid
• before the substrate binds, the active site is not exactly complementary to it
• as the substrate binds, it induces the active site to change shape, so the active site moulds itself around the substrate, giving a close fit
• this change in shape puts strain on bonds in the substrate, so they break more easily (or holds substrates in positions where new bonds form more easily)
• this lowers the activation energy of the reaction
• once the products are released, the active site returns to its original shape
Advantages over the lock and key model:
• it explains how the enzyme lowers activation energy
• it explains why some enzymes can bind a range of similar substrates
• it fits evidence, such as X-ray crystallography, that enzymes change shape when the substrate bindsSpecificity is still explained: only a substrate of the right shape and charge can bind and induce the correct change in the active site.Think of a glove: it has roughly the shape of a hand, but only fits closely once the hand is inside.
• the active site is flexible, not rigid
• before the substrate binds, the active site is not exactly complementary to it
• as the substrate binds, it induces the active site to change shape, so the active site moulds itself around the substrate, giving a close fit
• this change in shape puts strain on bonds in the substrate, so they break more easily (or holds substrates in positions where new bonds form more easily)
• this lowers the activation energy of the reaction
• once the products are released, the active site returns to its original shape
Advantages over the lock and key model:• it explains how the enzyme lowers activation energy
• it explains why some enzymes can bind a range of similar substrates
• it fits evidence, such as X-ray crystallography, that enzymes change shape when the substrate bindsSpecificity is still explained: only a substrate of the right shape and charge can bind and induce the correct change in the active site.Think of a glove: it has roughly the shape of a hand, but only fits closely once the hand is inside.