ABSTRACT

Enzymes are catalysts that are responsible for accelerating nearly all the chemical reactions occurring in the human body, reactions that are normally infinitely slow but are essential for life. It has been shown that the best way to study enzyme-substrate interactions is to determine the crystal structures of an enzyme and of the enzyme with substrate or inhibitor bound to it. A completely different enzyme system, Δ5-3-ketosteroid isomerase functions like aconitase as an isomerase; it causes abstraction of a hydrogen atom and transfers it to a neighboring carbon atom. Changes in the citrate molecule provide compounds that can be used to probe the mode of activity of citrate-utilizing enzymes. The citrate lyases, which break down citrate into acetate and oxaloacetate comprise two enzymes, one bacterial and one mammalian; they require metal ions for activity and are inhibited in various ways and to various degrees by hydroxycitrates.