Apoenzyme, defined

Coenzymes facilitate chemical reactions through a range of different reaction mechanisms, some of which will be discussed in detail in this review. However, in all cases structural features of the coenzyme allow particular reactions to proceed along a mechanistic pathway in which reaction intermediates are more thermodynamically and kinetically accessible. When incorporated into apoen-zyme active sites, the coenzyme reactivity is influenced by a well-defined array of amino acid functional groups. For a given coenzyme, the particular array of amino acids presented by the different apoenzymes can drastically alter the degree of rate acceleration and product turnover and can specify the nature of the reaction catalyzed. 

Terms in bold are defined in the enzyme 191 cofactor 191 coenzyme 191 prosthetic group 192 holoenzyme 192 apoenzyme 192 apoprotein 192 active site 193 substrate 193 ground state 193 standard free-energy change (AG°) 194... 

Define substrate, cofactor, prosthetic group, apoenzyme, and holoenzyme. 

Enzyme repression is defined as a relative decrease, resulting from the exposure of cells to a given substance, in the rate of synthesis of a particular apoenzyme [35]. 

Certain classes of enzymes require small, auxiliary, nonprotein molecules called cofactors, coenzymes, and prosthetic groups. Definitions for these three terms are somewhat arbitrary and, in fact, the term cofactor will be used in the following chapters to represent broadly the identity and functional roles of cocatalysts. The roles of cofactors are structural, functional, or both. They provide the enzyme with the chemical or photochemical capabilities lacking in the normal amino acid side chains. An enzyme devoid of a cofactor is called an apoenzyme. Apoenzymes are catalytically inactive. The active complex of the protein and the cofactor is termed a holoenzyme. The cocatalysts can be defined on the basis of the catalytic functions that are mediated (76). 

---