Bke2 Biochemistry Lectures

Lecture 13: Active sites and enzyme mechanisms: a closer look
Reading material: Horton, Chapter 6 (& 7) (Stryer, Chapter 8).

Abstract: In this lecture we take a closer look at how enzymes carry out catalysis of chemical reactions by examining in detail how serine proteases cleave polypeptide chains. We also examine some of the most common types of enzymes, and take a look at different cofactors that are used by proteins to complement their repertoire of chemical reagents.

The cofactors are of two kinds, essential ions and coenzymes. A further division can be made between cosubstrates and prosthetic groups. There are numerous coenzymes which participate in metabolism. ATP is frequently involved in group transfer reactions, particularly phosphoryl group transfer reactions catalysed by kinases. NAD and NADP are the cofactors for large groups of dehydrogenases and reductases and participate in two-electron transfer reactions. NAD is used mainly in catabolic pathways while NADP is used in anabolic reactions. FMN and FAD are tightly bound coenzymes that can accept/donate two electrons, one at the time.

During the conversion of glucose to pyruvate via the glycolysis pathway, a total of 2 ATP and 2 NADH are gained. Kinases, dehydrogenases and isomerases are important enzymes in the pathway. Kinases transfer a phosphate group to or from ATP. They consist of at least two domains, one of which binds ATP and the other the substrate. Conformational changes play an important role in the catalysis carried out by these enzymes. Phosphofructokinase is particularly important in the control of glycolysis.

Key concepts:
Cofactor, essential ions, coenzyme, cosubstrate, prosthetic group
Apoenzyme, holoenzyme
Enzyme families
Induced fit

Key reactions:
Phosphoryl transfer (kinases)
Isomerization (isomerases)
Redox reactions (NAD-dependent dehydrogenases)

Links:

Lecture index

[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35]