Enzymes

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1

enzyme

Functional proteins that catalyze biological reactions; involved in all essential body reactions and found in all body tissues; found in serum following cellular injury or from degraded cells; decrease the amount of free energy needed to activate a specific reaction and accelerate reactions; not altered or consumed; reusable

2

holoenzyme

forms functional unit that consists of apoenzyme and cofactor/coenzyme

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cofactors

non-protein substances (“inorganic or inorganic/nonprotein entities") that are necessary for some normal enzymatic reactions to occur; influence reaction rates

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minerals

usually inorganic and are cofactors, Mg, FE, Zn

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coenzyme

an organic cofactor, carbon based, that has a structure related to vitamins

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proenzyme/zymogen

inactive enzyme

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active site

Specific area of the enzyme structure that participates in the reaction(s)/interacts with the substrate

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allosteric site

Non-active site that may interact with other substances resulting in overall enzyme shape change; subset of enzymes that are involved in the control and regulation of biological processes

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isoenzymes

Same enzyme that is structurally different that catalyze the same reaction; multimolecular form, similar catalytic activity, differing biochemical or immunological characteristics, and can detect by different electrophoresis and absorption patterns or reaction with specific antibodies

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activator

inorganic cofactor material such as minerals

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apoenzyme

a heat-labile protein portion of the enzyme which requires a coenzyme for full catalytic activity

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prosthetic group

bound tightly enzymes

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enzyme kinetics

Reactions occur spontaneously if energy is available; Enzymes lower the activation energy for the chemical reactions

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activation energy

Excess energy that raises all molecules at a certain temperature to the activation state

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substrate

the substance on which an enzyme reacts

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enzyme-substrate product

Physical binding of a substrate to the active site of enzyme

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absolute specificity

Enzyme combines with only one substrate and catalyzes one reaction

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group specificity

Combine with all substrates containing a specific chemical group

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bond specificity

Enzymes specific to certain chemical bonds

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stereoisomerism

Enzymes that mainly combine with only one isomer of a particular compound

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Michaelis-Menten

Relationship of the reaction velocity/rate to the substrate concentration

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Michaelis-Menten Constant (Km)

The substrate concentration in moles per liter when the initial velocity is ½ V max

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first order kinetics

Rate is directly proportional to substrate concentration

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zero order kinetics

Plateau is reached; depends only on enzyme concentration

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Michaelis-Menten Equation

Equation used to distinguish different kinds of inhibition; V0: velocity/rate of enzymatic activity; Vmax: The maximal rate of reaction when the enzyme is saturated; Km: (constant)the substrate concentration that produces ½ of the maximal velocity; S: substrate concentration

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enzyme concentration

the higher the level, the faster the reaction

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7.0-8.0

pH at which most reactions occur; changes can denature enzymes

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37 Celsius

the temperature at which most reactions occur; increasing temperature increases rate of reaction; excessively high or low temperatures denature enzymes

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inhibitors

Presence can interfere with a reaction can be reversible or irreversible

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systematic name

Describes the nature of the reaction catalyzed

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recommended name

Working or practical name

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numerical code

First digit places enzyme in a class; Second and third digit represent subclass(s) of the enzyme; Fourth digit specific serial number in a subclass

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plasma specific enzymes

have a very definite/ specific function in the plasma, the normal site of action; concentration is greater than in most tissues; often synthesized in the liver; includes plasmin and thrombin

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non-plasma specific enzymes

have no known physiological function in the plasma; some are secreted in the plasma; Increased number of this type seen with cell disruption or death

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Oxidoreductase

Involved in oxidation-reduction reactions; includes LDH, G6PD

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transferase

Transfer functional groups from one substrate to another; includes AST, ALT

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hydrolase

Catalyze the hydrolysis of various bonds; includes acid phophatase, lipase

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lyase

Catalyze removal of groups from substrates without hydrolysis, product has double bonds; includes aldolase, decarboxylase

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isomerase

Involved in molecular rearrangements; includes glucose phosphate isomerase

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ligase

Catabolism reactions with cleavage of ATP; includes GSH

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oxidoreductases

lactate dehydrogenase, glucose-6-phosphate dehydrogenase, glutamate dehydrogenase

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transferases

aspartate aminotransferase, alanine aminotransferase, creatine kinase, and y-glutamyl-transferase

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hydrolases

alkaline phosphatase, acid phosphatase, a-amylase, cholinesterase, chymotrypsin, elastase-1, 5-nucleotide, triacyglycerol, lipase, and trypsin

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lysases

aldolase

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isomerases

triosephosphate isomerase

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ligases

glutathione synthetase