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3.2 Properties and Catalytic Mechanisms of Enzymes
3.3 Kinetics of Enzyme-Catalyzed Reactions 3.4 Regulation of Enzyme Activity 3.5 Nomenclature and Classification of Enzymes
dialysis or ultrafiltration. NAD, NADP, etc.
small organic molecules coenzyme metal ion
Iron, magnesium, cobalt, manganese
Functions of small organic molecules：
3.6 Clinical Applications of Enzymes
3.1 Structure and Function
of Enzymes
3.1.1 structure of enzymes
3.1.1.1 composition of Enzyme Molecules
Simple enzymes——proteins enzymes Conjugated enzymes (holoenzyme) apoenzyme
（1）producing site :
living cells
（2）property :
most——proteins
a few——RNA DNA
（3）function : biochemical catalyzation
OUTLINE
3.1 Structure and Function of Enzymes
approximation and orientation of reactants
as bridge between substrate and enzyme
neutralize negative charges to decrease electrostatic repulsion
ቤተ መጻሕፍቲ ባይዱ
3.1.1.2 monomeric enzymes, oligomeric enzymes and multienzyme complex
monomeric enzyme：only contain a
polypeptide chain with tertiary structure. oligomeric enzyme：contain two or more polypeptide chains associated by noncovalent bonds.
act as carriers to transfer electrons, protons（质子） or other groups.
TABLE 3-1 Cofactors of enzymes
Coenzymes Nicotinamide adenine dinucleotide (NAD+) Nicotinamide adenine dinucleotide phosphate (NADP+) Flavin adenine dinucleotide (FAD) Flavin mononucleotide (FMN) Thiamine pyrophosphate (TPP) Coenzyme A (CoA) Pyridoxal phosphate Biotin Tetrahydrofolate 5-deoxyadenosyl cobalamine Transferred groups H+, e H+, e H H -CHO (aldehyde) R-CO- (acyl) -NH2 CO2 “C”(one carbon unit ) CH3、-CnH2n +1(alkyl) Vitamins V-pp V-pp V-B2 V-B2 V-B1 Pantothenic acid V-B6 Biotin Folic acid V-B12
cofactor
prosthetic group
coenzyme
Holoenzyme = Apoenzyme + Cofactors
Cofactors are small organic（有机的） molecules or inorganic（无机的）ions required for enzyme activities.
metal-activated enzyme
bind metal ion less tightly metal ion is essential for activity
Functions of metal ion：
stabilize enzyme conformation
participate in reaction by transferring electrons
small organic molecules coenzyme metal ion
Iron, magnesium, cobalt, manganese
(Fe)
(Mg)
(Co)
(Mn)
metalloenzyme
bind metal ion tightly metal ion is retained throughout purification
Prosthetic group:
tightly bond with apoenzyme and can not be removed by dialysis（分离，透析） or ultrafiltration. FAD, metal, etc.
Coenzyme:
loosely bond with apoenzyme and can be removed by
Chapter 3
Enzymes
What is enzyme?
Enzymes are biocatalysts with high specificity and highly catalytic efficency produced by living cells.
Besides proteins, ribozymes and deoxyribozymes are also enzymes.
