Ch. 13 - Enzymes (GGT - G6PD) (RVSP) Flashcards Preview

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Flashcards in Ch. 13 - Enzymes (GGT - G6PD) (RVSP) Deck (114):
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Enzyme involved in the transfer of gamma-glutamyl residue from gamma-glutamyl peptides to amino acids, H2O, and other small peptides

Gamma-glutamyltransferase (GGT)

1

Serves as the gamma-glutamyl donor in most biologic systems

Glutathione

2

3 functions of GGT

- synthesis of peptides and proteins
- regulation of tissue glutathione levels
- transport of amino acids across cell membranes

3

Tissue sources of GGT

Kidney
Brain
Prostate
Pancreas
Liver

4

Enzyme used for evaluation of liver and biliary system disorders

GGT

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Enzyme elevated in all hepatobiliary disorders

GGT

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Enzyme increased in patients receiving enzyme-inducing drugs

GGT

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Elevated enzyme in chronic alcoholism

GGT

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Substrate for GGT analysis

Gamma-glutamyl-p-nitroanilide

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Absorbance range in GGT analysis

405-420 nm

10

Length of time and temperature that GGT activity is stable

1 week at 4°C

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Reference ranges for GGT

M: 6-55 U/L (37°C) (0.1 - 0.9 ukat/L)
F: 5-38 U/L (37°C) (0.1 - 0.6 ukat/L)

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Class of amylase

Hydrolase

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Enzyme that catalyzes the breakdown of starch and glycogen

Amylase (AMY)

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Enzyme that attacks only alpha, 1-4 glycosidic bonds

Alpha-AMY

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Degradation products produced after alpha-AMY attacks the alpha, 1-4 glycosidic bonds

- glucose
- maltose
- dextrins

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Intermediate chains consisting of alpha, 1-6 branching linkages

Dextrins

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2 components of starch

Amylose
Amylopectin

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Component of starch; long, unbranched chain of glucose molcules, linked by alpha, 1-4 glycosidic bonds

Amylose

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Component of starch; branched-chain polysaccharide with alpha, 1-6 glycosidic linkages at the branch points

Amylopectin

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Important enzyme in the physiologic digestion of starches

AMY

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2 ions needed by AMY for its activation

Calcium ion (Ca2+)
Chloride ion (Cl-)

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2 major tissue sources of AMY

Acinar cells of the pancreas
Salivary glands

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Minor tissue sources of AMY

Skeletal muscle
Small intestine
Fallopian tubes
Urine

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Smallest enzyme

AMY

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Where digestion of starches start

Mouth

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Enzyme in the mouth that hydrolyzes starches

Salivary AMY

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Performs the major digestive action of starches once the polysaccharides reach the intestine

Pancreatic AMY

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Inactivates salivary AMY

Acidity of gastric contents

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Diagnostic significance of serum and urine AMY

Acute pancreatitis
Salivary gland lesions
Intraabdominal diseases
Renal insufficiency
Diabetic ketoacidosis
Hyperamylasemia

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Time when AMY levels begin to rise in acute pancreatitis

5-8 hours after onset of attack

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Time when AMY levels are at peak in acute pancreatitis

24 hours

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Time when AMY levels return to normal in acute pancreatitis

3-5 days

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Condition when the AMY molecule combines with immunoglobulins to form a complex that is too large to be filtered by the glomerulus

Macroamylasemia

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AMY isoenzyme derived from pancreatic tissue

P-type

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AMY isoenzyme derived from salivary gland tissue, fallopian tube and lung

S-type

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AMY isoenzymes that migrate the fastest in electrophoresis

S-type (S1, S2 and S3)

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AMY isoenzymes that migrate slowly in electrophoresis

P-type (P1, P2 and P3)

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Most commonly observed AMY isoenzyme fraction in electrophoresis

P2
S1
S2

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Predominant AMY isoenzyme in acute pancreatitis and renal failure

P3

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4 methods for AMY assay

- Amyloclastic/Iodometric method
- Saccharogenic method
- Chromolytic/Chromogenic Labelled Substrate method/Colorimetric
- Couple Enzyme Reaction/Continuous-monitoring technique

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AMY method; measures the disappearance of starch substrate

Amyloclastic

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AMY method; measures the appearance of the product (reducing sugars)

Saccharogenic

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AMY method; measures the increasing color from production of product coupled with a chromogenic dye

Chromogenic/Chromolytic/Colorimetric

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AMY method; coupling of several enzyme systems to monitor amylase activity

Continuous monitoring/Coupled Enzyme reaction

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Optimal pH for AMY activity

pH 6.9

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Length of time and temperature where serum and urine AMY is stable

1 week at RT
2 months at 4°C

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Reference ranges for AMY

Serum: 28-100 U/L (37°C) (0.5-1.7 ukat/L)
Urine: 1-15 U/h

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Enzyme that hydrolyzes the ester linkages of fats to produce alcohols and fatty acids

Lipase (LPS)

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Substrate requirement for LPS in order for activity to occur

Emulsion

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Accelerates LPS reactions

Colipase
Bile salt

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Major tissue source of LPS

Pancreas

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Minor tissue sources of LPS

Stomach
Intestine (small)

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Diagnostic significance of LPS

Acute pancreatitis

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Time when serum LPS activity rises after an attack of acute pancreatitis

4-8 hours

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Time when LPS levels peak in acute pancreatitis

24 hours

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Time when LPS levels decrease in acute pancreatitis

8-14 days

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Enzyme that is more specific for pancreatic disorders than AMY measurement

LPS

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LPS isoenzyme that is the most clinically specific and sensitive

L2

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Classic method for LPS; used an olive oil substrate

Cherry-Crandall method

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LPS method; measures the liberated fatty acids by titration after a 24-hour incubation period

Cherry-Crandall method

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Substrate in Cherry-Crandall method for LPS

Olive oil

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Substrate now used in Cherry-Crandall method for LPS; more pure form of triglyceride

Triolein

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LPS method; measures the rate of clearing n a solution for LPS activity

Turbidimetric methods

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Method for LPS; based on coupled reaction with enzymes such as peroxidase or glycerol kinase

Colorimetric methods

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Lenth of time and temperature when LPS acitivity is stable

1 week at RT
3 weeks at 4°C

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Reference range for LPS

<0.6 ukat/L)

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Enzyme class of G-6-PD

Oxidoreductase

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Tissue sources for G-6-PD

Adrenal cortex
Spleen
Thymus
Erythrocytes
Lymph nodes
Lactating mammary gland

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Inheritance pattern of G-6-PD deficiency

Inherited sex-linked trait

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Maintains NADPH in reduced form

G-6-PD

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Required to regenerate sulfhydryl-containing proteins (ex. glutathione) In its reduced state

NADPH

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Protects Hb from oxidizing agents

Glutathione (reduced form)

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Drug that causes Drug-induced Hemolytic Anemia (DIHA) during G-6-PD deficiency

Antimalarial drugs (Primaquine)

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Hemolytic anemia caused by antimalarial drugs (Primaquine) in the presence of G-6-PD deficiency

Drug-Induced Hemolytic Anemia (DIHA)

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Conditions of increased levels of G-6-PD

- MI
- Megaloblastic anemia

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Enzyme that does is not elevated during hepatic disorders

G-6-PD

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Specimen used for suspected G-6-PD enzyme deficiency

Red cell hemolysate

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Specimen used for suspected G-6-PD enzyme elevation

Serum

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Reference range for G-6-PD

7.9 - 16.3 U/g Hb (0.1 - 0.3 ukat/g Hb)

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Diagnostic significance of GGT

- Hepatobiliary disorders
- Enzyme inducing drugs
- Alcoholism (chronic)
- Acute pancreatitis
- Diabetes mellitus
- MI
- Differentiating source of ALP elevation

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Enzyme-inducing drugs

Warfarin
Phenobarbital
Phenytoin

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Method of GGT measurement

Sasz Method

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2 substrates used in Sasz method for GGT

- L-λ-glutamyl-p-nitroanilide (yellow; 405 nm)
- 5-amino-2-nitrobenzoate (410 nm)

84

Salivary gland lesions related to AMY elevation

Mumps
Parotitis

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Intraabdominal disease related to AMY elevations

Perforated peptic ulcer
Intestinal obstruction
Cholecystitis
Ruptured ectopic pregnancy
Acute appendicitis
Mesenteric infarction

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Tissue sources of S-type AMY

Salivary gland tissues
Fallopian tubes
Lungs

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Where does P-type AMY predominate?

Urine

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Where does S-type AMY predominate?

Serum

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AMY mtd; measures the disappearance in initial dark blue color of starch-iodine complex

Amyloclastic/Iodometric mtd

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Reference mtd for AMY

Saccharogenic Mtd

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Number of mg glucose in 30 mins at 37°C at specific assay conditions

Somogyi units

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Wavelength for coupled enzyme reaction for AMY

340 nm

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Substrate for coupled enzyme reaction of AMY

Maltotetrase/maltopentoase

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Inhibits S-type AMY

Wheat germ lectin

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Causes falsely normal levels AMY

Plasma triglycerides

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Inhibits serum AMS activity leading to falsely normal levels in acute pancreatitis with hyperlipemia

Plasma triglycerides

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Causes falsely increased levels of AMY

Morphine
Opiates

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Causes falsely decreased of AMY levels

Oxalates
Citrates

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Conversion factor from Somogyi units to IU

1.85

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Enzyme class of lipase

Hydrolase

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How many days does LPS elevations persist?

5 days

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pH for LPS activity

pH 8.6 - 9.0

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Intraabdominal condition related to LPS elevations

Penetrating duodenal ulcers
Intestinal obstruction
Perforated peptic ulcers
Acute cholecystitis

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Activators for LPS methods

Albumin/ionized calcium

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Inhibitors for LPS methods

Heavy metals (ex: quinine)

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5 methods for LPS activity

Turbidimetric Enzyme Reaction
Cherry-Crandall Method (Titrimetric)
Tietz-Borden Mtd
Sigma Tietx
Colorimetric Mtd

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Substrates for Turbidimetric Enzyme reaction for LPS

Olive oil
Triolein

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Mtd for LPS; decrease in turbidity is measured as LPS hydrolyzes the turbid substrate fat emulsion

Turbidimetric Enzyme Reaction

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Mtd for LPS; measures liberated fatty acids released by alkaline titration after 24 hrs incubation

Cherry-Crandall Mtd (Titrimetric)

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Indicator in Cherry-Crandall Mtd for LPS

Phenolphthalein (salmon color)

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Indicator used in Sigma Tietx

Thymolphthalein (blue color)

112

Enzymes used in the Colorimetric mtd for LPS

Peroxidase
Glycerol kinase

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Causes false decrease in LPS levels

Hemolysis