Biochemistry Lecture 6

8/3/2019 Biochemistry Lecture 6

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Study of Enzymes &

Coenzymes

Lecture No. 6











How important are enzymes?

Enzymes are essential to sustain life becausemost chemical reactions in biological cells wouldoccur too slowly, or would lead to different

products, without enzymes. A malfunction (mutation, overproduction,

underproduction or deletion) of a single criticalenzyme can lead to a severe disease.

Enzymes work by lowering the activation energyof a reaction, thus allowing the reaction toproceed much faster.







Terminologies Substrate ± substance reacted upon by an enzyme

Apoenzyme ± is an enzyme without its cofactor; it is the proteinmolecule to which a coenzyme will bind to produce the holoenzyme.

Ex. RNA polymerase

Holoenzyme ± the active and operative form of an enzyme. This isthe complete fully functioning enzyme. It is the combination of anapoenzyme with its cofactor.

Proenzymes ± are inactive precursors of enzymes. Ex. Zymogen,pepsinogen

Kinase ± substance used to activate the proenzyme.

Coenzyme is an organic non-protein molecule that is functional artof an enzyme. They are generally defined as cofactors.

Antienzyme ± is a substance that neutralizes or counteracts the

action of an enzyme or they refer to an inhibitory enzyme or anantibody to an enzyme that retards, inhibits, or destroys enzymicactivity.

Isoenzyme or isozymes are enzymes that differ in amino acidsequence but catalyze the same chemical reaction (LDH1-5)





Class Class Name Examples by trivial name

1 Oxidoreductase Dehydrogenase, oxidase,

peroxidase, catalase

2 Transferase Kinase, transaminase,

transketolase

3 Hydrolase Esterase, peptidase,digestive enzymes

4 Lyases Decarboxylase, aldolase,

deaminase, fumarase

5 Isomerase Epimerase, mutase

6 Ligases Carboxylase, acetyl CoA

carboxylase



















































Other Coenzymes

Vitamin Coenzyme Function

Niacin NAD, NADP Oxidation-reduction

Pyridoxine Pyridoxal

phosphate

Various reactions involved in

AA activation

Lipoic acid Lipoamide Acyl group

activation;oxidation-reduction

Vitamin B12 Adenosylcobalamine

Isomerization and methyl

group transfer































Chymotrypsin (Spacefill)



































Other Disorders of Enzymatic Defect

Metabolic Disorder Enzymatic defect

Agammaglobulinemia Inability to form gamma

globulins

Alkaptonuria Absence of hepatichomogentisic acid

Gout Excessive production of

uric acid

Hemohilia A, B, & G Deficiency of clotting

factors

Histidinemia Deficiency of histidase



More Metabolic Disoders

Sickle cell anemia Presence of abnormalhemoglobins

Thalassemia Presence of abnormal

hemoglobins

Von Gierke¶s disease Deficiency of glucose-6-phosphatase

Porphyria Increased excretion of

uroporphyrins resulting to

lavender teeth, burgundy red

urine

Maple syrup disease Absence of decarboxylase

enzyme for branched chain

amino acids

















S



Summary Enzymes are biologic catalysts that increase the

rates of biochemical processes but are themselvesunchanged. Most (but not all) enzymes are proteins.

In enzyme catalysis, one or more substrates arebound at the active sites of an enzyme, to form theenzyme-substrate complex; products are thenreleased.

The rate of chemical reaction is determined byreactant concentration and by the rate constant.

All catalysts function by lowering the activationenergy for a reaction. In doing so, they do not affectchemical equilibrium but only increase rates.

Many enzymes utilize coenzymes in their functions;others require specific metal ions. A number of coenzymes are closely related to vitamins requiredin the diet.

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Biochemistry Lecture 6