The Krebs (citric acid) cycle is a group of reactions in the respiratory chain.
In the cycle, citrate is isomerized to isocitrate.
..........................................citrate ............................aconitate........................isocitrate
Citrate has three -COO- groups with an -OH group on the C3.
The enzyme aconitase catalyses the dehydration of citrate so that aconitate is formed; note the C=C bond.
Then the same enzyme catalyses the hydration of aconitate to produce isocitrate; the -OH is now on the C2.
Since enzymes are catalysts, we would have expected the reforming of the original citrate, but this does not happen.
