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In the field of biochemistry, the specificity constant (also called kinetic efficiency or ), is a measure of how efficiently an enzyme converts substrates into products. A comparison of specificity constants can also be used as a measure of the preference of an enzyme for different substrates (i.e., substrate specificity). The higher the specificity constant, the more the enzyme "prefers" that substrate. The following equation, known as the Michaelis–Menten model, is used to describe the kinetics of enzymes: : where E, S, ES, and P represent enzyme, substrate, enzyme–substrate complex, and product respectively. The symbols , , and denote the rate constants for the "forward" binding and "reverse" unbinding of substrate, and for the "catalytic" conversion of substrate into product respectively. The Michaelis constant in turn is defined as follows: : ) is the rate of product formation when the enzyme is saturated with substrate and therefore reflects the enzyme's maximum rate. The rate of product formation is dependent on both how well the enzyme binds substrate and how fast the enzyme converts substrate into product once substrate is bound. For a kinetically perfect enzyme, every encounter between enzyme and substrate leads to product and hence the reaction velocity is only limited by the rate the enzyme encounters substrate in solution. Hence the upper limit for is equal to rate of substrate diffusion which is between108 and 109 s−1M−1. == See also == * Turnover number 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Specificity constant」の詳細全文を読む スポンサード リンク
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