Review Journal on Enzymes ("The Physiological Sources of, Clinical Significance of, and Laboratory-Testing Methods for Determining Enzyme Levels" | P) Flashcards
What is the characteristic of enzymes?
These are organic molecules
What is the fxn of enzymes?
These accelerate biochemical rxns but emerge from the rxn unchanged
What is the meaning and purpose of abnormal lvls of plasma enzymes?
These are highly suggestive of damaged cells and provide clues to parts of the body that may be involved in disease processes
What are the purposes of measuring the enzyme lvls in the clinical lab?
1) To identify the site of damage
2) To quantify the amt of damage
What is the meaning of LD?
Lactate dehydrogenase
What is the meaning of AST?
Aspartate aminotransferase
What is the meaning of ALT?
Alanine aminotransferase
What is the meaning of ALP?
Alkaline phosphatase
What is the meaning of GGT?
Gamma-glutamyltransferase
What are the characteristics of LD?
1) It is a tetrameric enzyme
2) It has 2 distinct subunits
3) It has 6 isoenzymes
What are the 2 distinct subunits present in LD?
1) M
2) H
Where can LD be found?
1) Cardiac and skeletal muscles
2) Liver
3) Kidneys
4) Erythrocytes
5) Leukocytes
6) Lungs
7) Lymph nodes
8) Spleen
9) Brain
What is the fxn of LD?
It catalyzes the redox conversion of lactate to pyruvate / it catalyzes the reversible conversion of pyruvate to lactate in a redox rxn
What are the 6 isoenzymes of LD?
1) LD1
2) LD2
3) LD3
4) LD4
5) LD5
* 6) LD6
LD1 consists of what subunits?
HHHH subunits
LD2 consists of what subunits?
HHHM subunits
Where are LD1 and LD2 predominantly found?
1) Heart
2) Erythrocytes
LD3 consists of what subunits?
HHMM subunits
Where is LD3 found?
In the lungs
LD4 consists of what subunits?
HMMM subunits
LD5 consists of what subunits?
MMMM subunits
Where are LD4 and LD5 found?
In the liver
What is the meaning of MI?
Myocardial infarction
What is the meaning of NAD?
Nicotinamide adenine dinucleotide
What is the meaning of NADH?
Reduced nicotinamide adenine dinucleotide
What are aminotransferases and what is its fxn?
These are a grp of enzymes that catalyze the conversion of AAs to 2-oxo-acids by transfer of amino grps
Where are the highest lvls of AST present?
1) Liver
2) Cardiac muscle
3) Skeletal muscle
Where are the smaller amts of AST present?
1) Kidneys
2) Pancreas
3) Erythrocytes
Where is ALT predominantly present?
Liver
What is the fxn of ALP?
It catalyzes the hydrolysis of various phosphomonoesters at an alkaline pH
Where are the highest concentrations of ALP found?
1) Bone
2) Liver
3) Spleen
4) Intestine
5) Placenta
6) Kidneys
What are the diff isoenzymes of ALP?
1) Bone
2) Liver
3) Placenta
Isoenzyme analysis is of limited clinical use due to what?
Due to ineffective methods of separation and the availability of more efficient tests for clinical dx
What are the fxns of GGT?
1) It catalyzes the transfer of the gamma(sign)-glutamyl residue from gamma(sign)-glutamyl peptides to AAs
2) It is responsible for the catabolism of extracellular glutathione
What is the characteristic of GGT?
It is an epithelial enzyme
Where is GGT present?
1) Kidney
2) Brain
3) Prostate
4) Pancreas
5) Liver tissue
LD lvls are increased in several disorders due to its what?
Due to its presence in a variety of tissues
At what conditions are the most dramatic increase of LD lvls observed?
1) Prehepatic disorders
2) Hemolytic disease
3) Testicular and germ cell tumors
4) Acute MI
What happens to LD lvls when in presence of the said conditions where it is increased?
1) It increases 12 hrs after an MI
2) It peaks in 2 days
3) It returns back to normal lvls in 7 - 14 days
What LD isoenzyme normally predominate in the blood?
Plasma LD2 lvls
What LD isoenzyme follows plasma LD2 in terms of predominating in the blood?
LD1 lvls
What happens if there is a presence of damaged cardiac tissue in MI?
LD1 lvls increase, w/c triggers a reversal in w/c LD1 lvls become > LD2 lvls
What is the reason why isoenzyme analysis now became outdated?
Isoenzyme analysis has now became outdated due to the availability of more sensitive and sp cardiac markers
Give an ex of sp cardiac marker
Troponin
Where can troponin be used / help?
In terms of the dx of MIs
Currently, laboratorians mostly use LD as what?
As a nonspecific screening or monitoring tool
What is the purpose of mostly using LD as a nonspecific screening or monitoring tool by the laboratorians?
To determine the extent of tissue damage
What is the reference range for LD?
125 - 220 U/L
What are the clinically significant aminotransferases?
1) ALT
2) AST
What is the purpose of ALT and AST?
Both are markers of liver disease
What is the comparison bet ALT and AST?
ALT is more liver sp > AST
At what conditions / disorders are AST lvls significantly increased?
1) Skeletomuscular disorders
2) Pulmonary embolism
What happens to ALT lvls and what is its relationship w/ AST lvls in cases of acute inflammatory conditions of the liver?
ALT lvls are higher > AST lvls
Why are ALT lvls higher > AST lvls in cases of acute inflammatory conditions of the liver?
Because ALT has a half-life of 16 - 24 hrs
Increased ALT lvls have been associated w/ what and what is the result of these accdg to some studies?
These lvls have been associated w/ deaths from liver disease and all-cause mortality in some studies
What is the reference range for ALT?
7 - 45 U/L
What is the reference range for AST?
5 - 35 U/L
ALP lvls are highly increased in cases of what disorders?
1) Hepatobiliary disorders
2) Bone disorders
ALP lvls are normally increased during what instances?
1) Pregnancy
2) Growing children
Why are ALP lvls normally increased during pregnancy?
Due to placental fraction of ALP
Why are ALP lvls normally increased during the growth of children?
Due to bone fraction of ALP
At what disorders are intestinal ALP lvls increased?
Disorders of the:
1) Digestive tract
2) Liver
At what condition / disorder are ALP lvls decreased?
Inherited hyperphosphatasia
The reference range for ALP varies w/ what?
1) Age
2) Sex
Higher lvls of reference range for ALP are present in what age grp?
Younger individuals > older individuals
Higher lvls of reference range for ALP are present in what sex?
Men > women
Why are the reference range for ALP lvls are higher for younger individuals > older individuals and men > women?
Probably due to bone-fraction measurements
GGT lvls are mainly elevated in what disorders?
1) Hepatobiliary disorders
2) Liver disorders
GGT lvls are also increased in what instances for pts?
1) In pts w/ chronic alcoholism
2) Pts who take enzyme-inducing drugs
3) Pts having pancreatitis
4) Pts having DM
What are the exs of enzyme-inducing drugs that can cause increased GGT lvls?
1) Warfarin
2) Phenytoin
High GGT lvls are also associated w/ what?
W/ high rates of all-cause mortality
What is the reference range for GGT for men?
6 - 55 U/L
What is the reference range for GGT for women?
5 - 38 U/L
Why are the reference range for GGT lvls are lower in females compared to males?
Due to higher lvls of estrogen and progesterone
What are the characteristics of measurement of enzymes?
1) It is standardized
2) It is simple
3) It is inexpensive
4) It requires no special preparation for the pt
True or False
Small quantity of enzymes are normally available in the blood
True
What is done due to the reason that small quantity of enzymes normally available in blood?
The rate of rxn is measured photometrically, related to the activity of the enzyme
What is the relationship bet enzyme activity and concentration of the enzyme?
Enzyme activity is proportional to the concentration of the enzyme
What are the preferred type of sx for enzyme analysis?
1) Serum
2) Heparinized plasma
How can laboratorians measure LD activity and what is its principle?
By gauging the A of coenzyme NAD as it is changed to NADH while lactate is oxidized to pyruvate
What is the principle of rxn of lactate being oxidized to pyruvate?
Lactate + NAD^+ Pyruvate + NADH + H
The rxn of lactate being oxidized to pyruvate is derived from what process?
Glycolysis
What is the purpose of glycolysis?
It is the biochemical pathway for metabolism of glucose in all living cells
What are the sx considerations and storage considerations for determination of LD lvls?
1) Sxs must be free from hemolysis
2) Sxs must be stored at room temp
3) Sx must be analyzed within 48 hrs after sx collection
Why must sxs be free from hemolysis in determination of LD lvls?
Because LD lvls are 100- to 150-fold higher in RBCs > in serum
How are AST and ALT activity measured?
By measuring the change in A as aspartate and alanine transfer their amino grp to the appropriate respective alpha(sign)-keto acids
What is the coenzyme for rxns in connection w/ AST and ALT activity?
Pyridoxal-5-phosphate
What is the principle of rxn for AST?
Aspartate + alpha(sign)-Ketoglutarate Oxaloacetate + Glutamate
Oxaloacetate + NADH + H^+ + Malate + NAD^+
What is the principle of rxn for ALT?
Alanine + alpha(sign)-Ketoglutarate Pyruvate + Glutamate
Pyruvate + NADH + H^+ Lactate + NAD^+
What is the relationship bet change in A and concentration of AST?
Change in A is directly proportional to the concentration of AST
What is the relationship bet change in A and concentration of ALT?
Change in A is directly proportional to the concentration of ALT
ALT and AST rxns are extremely impt for what?
Synthesis and degradation of AAs
Oxaloacetate and pyruvate are oxidized by what?
Tricarboxylic cycle (Krebs cycle)
What is the purpose of oxidizing oxaloacetate and pyruvate via Krebs cycle?
To provide intermediate products
What is the fxn of the intermediate products that came from the oxidation of oxaloacetate and pyruvate via Krebs cycle?
To generate energy for living cells
What are the sx and storage considerations for determination of AST lvls?
1) Sxs must be free from hemolysis
2) For optimal results, sxs must be stored at ref temp
3) Analyze the sx within 3 - 4 days after sx collection
What are the sx and storage considerations for determination of ALT lvls?
1) For optimal results, sxs must be stored at ref temp
2) The sxs should be analyzed within 3 - 4 days after sx collection
Are ALT lvls are affected by any interference from erythrocytes?
No, because ALT lvls are unaffected by any interference from RBCs
ALP activity is measured by a method devised by what / whom?
Bowers and McComb
What is involved in the method to measure ALP activity devised by Bowers and McComb?
It involves the calculation of activity based on molar absorptivity of p-nitrophenol
What is the characteristic of para-nitrophenylphosphate?
It is a colorless compound
What happens to para-nitrophenylphosphate in measuring the ALP activity (devised by Bowers and McComb)?
It is hydrolyzed to a yellow-colored p-nitrophenol
Increase in A (in Bowers and McComb) can be measured in what rxn?
*p-Nitrophenylphosphate p-Nitrophenol + Phosphate ion
What is the relationship bet A of p-nitrophenol and ALP activity?
The increase in A of p-nitrophenol is directly proportional to ALP activity
What are the sx considerations for ALP analysis?
1) Sxs collected must be free of hemolysis
2) Sxs must analyzed soon after collection
3) Pt must not eat a high-fat meal before sx collection
4) Fasting sxs are not recommended because the interference is negligible
Why should the pt must not eat a high-fat meal prior to sx collection (in determination of ALP lvls)?
Because if the pt ate a high-fat meal prior to sx collection may also cause falsely increased values due to the intestinal fraction for ALP
When is GGT activity measured?
When gamma(sign)-glytamyl-p-nitroanilide transfer its gamma(sign)-glytamyl residue to glycylglycine
When gamma(sign)-glytamyl-p-nitroanilide transfer its gamma(sign)-glytamyl residue to glycylglycine, this results to the formation of what?
p-Nitroaniline
What is p-Nitroaniline?
It is a chromagen
What is the principle of rxn for the formation of p-Nitroaniline?
gamma(sign)-Glutamyl - p-nitroanilide + Glycylglycine
gamma(sign)-Glutamyl - glycylglycine + p-Nitroaniline
What is the relationship bet the A of p-Nitroaniline to the activity of GGT?
The A of p-Nitroaniline is directly proportional to the activity of GGT
What is the stability of p-Nitroaniline?
It is stable in serum sxs for 1 wk at ref temp
What is the importance of LD, AST, ALT, ALP, and GGT?
These are the enzymes that are clinically significant in various disorders including conditions of the liver
At what disorders / conditions are LD lvls most predominant?
1) Pre-hepatic disorders
2) Hemolytic disorders
Why are LD lvls most predominant in pre-hepatic and other hemolytic disorders?
Due to its presence in erythrocytes
At what disorders are ALT and AST lvls predominant?
Hepatic disorders
What is the comparison bet ALT and AST?
ALT is more liver sp > AST
At what disorders are ALP and GGT increased?
Post-hepatic disorders
What is the purpose of GGT?
It is associated w/ chronic alcoholism
What are the importance of increased activity w/ LD, ALT, AST, ALP, and GGT being detected?
1) These enzymes provides clues to the source of the clinical problem
2) These can be extremely valuable in the dx of the pt’s condition
