enzymes, lipids, cardiac markers Flashcards by Melissa May

isoenzymes:

are different molecular forms of the same enzyme
There are different Isoenzymes for different tissues

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Substrate inhibitors

An inhibitor that competes for an enzyme binding site

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Uncompetitive inhibitors

After the enzyme binds the substrate, this inhibitor binds the E-S complex

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Non-competitive inhibitor

Prevents substrate binding by altering the enzyme

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Examples of Co-factors

Mg2+
Cu+
Mn2+

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Oxidoreductases

LD (Lactate Dehydrogenase

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Transferase

Creatinine Kinase
GGTP
AST
ALT

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Hydrolase examples

Acid Phosphatase
Amylase
Alkaline Phosphatase

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Lysases

Aldolase

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factors affecting enzyme assays

Substrate Concentration
Temperature
pH

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Clinical assays are designed to follow:

Zero Order Kinetics

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Energy of Activation

The amount of energy required to convert reactants spontaneously to products

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Inhibitors

A substrate that slows the rate of an enzymatic reaction

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Holoenzyme

Complex of the apoenzyme, the inactive portion of the enzyme, and its cofactor(s)

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Co-factors

Non-protein chemical compounds required for the enzyme’s biological activity to occur

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The substrate conentration at which the velocity of the enzyme reaction is equal to 1/2 the max velocity

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Enzymes

Catalytic proteins present in all body cells

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Which enzyme is most elevated in alcoholic cirrhosis?

GGT

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Which 2 enzymes are most elevated in viral hepatitis?

AST
ALT

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Which enzyme facilitates carbohydrate breakdown?

Amylase

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You are unable to run alkaline phosphatase on your liver profile because the manufacturer has recalled the reagents. Which other enzyme(s) might you substitute which could give you information similar to alkaline phosphatase?

LAP
5”-nucleotidase

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You receive a grossly hemolyzed specimen for LD assay on a patient with suspected liver disease. What is the best course of action?

Always obtain a new sample since elevation could lead to a false interpretation of liver disease in light of the suspected diagnosis.

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Which enzyme/test pattern is diagnostic of MI?
A. Elevated CK with MB fraction present; LD elevated with a 1:2 flip; elevated AST, elevated troponin.
B. Elevated CK with MB fraction present; LD‑1 elevated; LD‑2 normal; normal AST, normal troponin.
C. Elevated CK with BB fraction; Normal LD, normal AST, normal troponin
D. Elevated CK with MM fraction, Elevated LD‑5, elevated AST, elevated troponin

A. Elevated CK with MB fraction present; LD elevated with a 1:2 flip; elevated AST, elevated troponin.

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Which enzyme is used in rape cases?

Acid phosphatase

Significantly elevated serum amylase with normal urine amylase and normal lipase indicates

Macroamylasemia

An acid phosphatase assay is severely elevated. It is treated with tartrate ion and the activity of the enzyme is inhibited showing a greatly diminished activity the second time the sample is assayed. What condition does this test result correlate with?

Prostatic Cancer

In the assay of an enzyme, zero order kinetics is best described by

Substrate is present in excess; rate of reaction is constant with time and dependent only on the concentration of enzyme in the system.

When measuring enzyme activity that occurs normally at 37C, if the instrument is operating 5 degrees C lower than the temperature prescribed for the method, the results will

be lower than expected

Enzymes that catalyze the transfer of groups between compounds are classified as

transferases

An International Unit (IU) of enzyme activity is the quantity of enzyme that

Converts one micromole of substrate to product per minute per liter

Which of the following is true concerning obstructive jaundice? A. Unconjugated bilirubin is greatly increased B. Conjugated bilirubin is decreased C. Conjugated is greatly increased D. Total bilirubin is normal

C. Conjugated is greatly increased

Which of the following statements best represents the change in viral hepatitis? A. conjugated bilirubin is greatly increased B. unconjugated bilirubin is greatly increased C. unconjugated bilirubin is increased D. total bilirubin is normal

A. conjugated bilirubin is greatly increased

Lipids have been given a bad rap lately. What are three good things they are responsible for?

Steroid hormone precursors, bile acid precursors, components of cell walls

Rank the following (highest to lowest) by the amount of triglyceride in the complex: HDL, chylomicron, LDL, VLDL.

Chylomicrons>VLDL>LDL>HDL

Which lipid is the precursor of steroid hormones?

Cholesterol

Which lipid is a component of arterial plaque?

Cholesterol

The turbid, or milky, appearance of serum after fat ingestion is termed postprandial lipemia. This lipemic appearance is caused by the presence of what substance?

Chylomicrons

Which lipid is the primary lipid in HDL?

Phospholipid

To provide reliable results, when should blood specimens for lipid studies be drawn?

In the fasting state, approximately 12 to 14 hours after eating.

Chylomicron

delivery of dietary lipid to hepatic and peripherial cells

VLDL

carries endogenous triglycerides from liver to peripherial tissues

LDL

carries cholesterol esters to tissues

HDL

takes cholesterol from tissues to the liver

When lipoprotein electrophoresis is performed at pH 8.6 with the use of agarose gel, which fraction migrates the fastest toward the anode?

HDL

Which lipid test is least affected by the fasting status of the patient?

CHOLESTEROL

Enzymatic methods for the determination of total cholesterol in serum utilize a cholesterol oxidase-peroxidase method. In this method, cholesterol oxidase reacts specifically with what?

Free cholesterol and fatty acids

Which apoprotein is inversely related to risk for coronary heart disease?

Apoprotein A-I

Current kinetic methods for quantifying serum triglycerides employ enzymatic hydrolysis. The hydrolysis of triglycerides may be accomplished by what enzyme?

LIPASE

Name a commonly used precipitating reagent which separates high-density lipoprotein cholesterol from other lipoprotein cholesterol fractions.

Heparin-manganese

Which of the following enzymes is common to all enzymatic methods for triglyceride measurement?

Glycerol kinase

Select the cut-off point for plasma or serum LDL cholesterol in a person with a history of coronary heart disease in whom therapeutic lifestyle changes should be initiated.

≥ 100 mg/dl

Lipoprotein (a), or Lp(a), is significant when elevated ins serum because it:

Is an independent risk factor for atherosclerosis

Select the reagent needed in the coupling enzyme reaction used to generate a colored product in the cholesterol oxidase method for cholesterol.

Phenol

Which statement best describes the clinical utility of plasma or serum myoglobin?

Levels below 100 ug/L on admission and 2-4 hours post admission help to exclude a diagnosis of acute MI

Which statement best describes the clinical utility of B-type natriuretic peptide (BNP)?

A normal test result (<100 pg/ml) helps rule out congestive heart failure in persons with symptoms associated with coronary insufficiency

Which test provides the earliest warning of increased risk of coronary artery disease?

High-sensitivity C-reactive protein

Which statement best describes the clinical utility of plasma homocysteine?

High plasma levels are associated with atherosclerosis and increased risk of thrombosis

What is the principle of the "direct" or "homogeneous" HDL cholesterol automated method which does not require sample preparation prior to testing? The direct HDL method:

Utilizes polymers and detergents that make the HDL cholesterol soluble while keeping the other lipoproteins insoluble