Enzymes: Transferases Flashcards
Once the alpha-ketoglutarate accepts the amine group, what is it converted to?
L-glutamate
What reaction do the aminotransferases catalyze?
The transfer of an amine group to an alpha-ketoglutarate.
What varies for each aminotransferase when the amino acid is donated?
The amino acid substrate that donates the amine group
What is required to transfer the amine group to alpha-ketoglutarate?
Pyridoxal-5-phosphate
What other name is pyridoxal-5-phosphate known as?
Vitamin B6
What does AST stand for?
Aspartate aminotransferase
What does ALT stand for?
Alanine aminotransferase
What is the pH optimum for AST and ALT?
7.3-7.8
How long is AST stable when refrigerated?
3-4 days
What reaction does AST catalyze?
The amine transfer from aspartic acid to alpha-ketoglutarate
What are the products formed when AST catalyzes a reaction?
Oxaloacetate and L-glutamate
Does hemolysis affect AST measurement?
Yes, it falsely increases AST activity due to AST being present in RBCs.
Where is AST found in highest concentrations?
Heart, liver, skeletal muscle
Where is AST found in smaller amounts?
Kidney, pancreas, spleen, lung, RBC
In what disease states is an elevated AST seen in?
Heart disease, liver disease, skeletal muscle disorders, pulmonary embolism, acute pancreatitis
Is an elevated AST diagnostic for an AMI?
No, it has limited diagnostic use due to it taking too long to increase (6-8 hours after pain onset).
In viral hepatitis, how many times the URL will AST be increased?
30-50x the URL
In toxic hepatitis, how many times the URL will AST be increased?
As high as 100x the URL
What reaction does ALT catalyze?
The transfer of an amine group on alanine to alpha-ketoglutarate
What products are formed in the reaction ALT catalyzes?
Pyruvate and glutamate
How long is ALT stable at refrigerated temperature?
3-4 days
Is ALT measurement affected by hemolysis?
No
Where is ALT found in highest concentration?
Liver
Where else can ALT be found in the body?
Widely distributed through the body in small amounts (heart, kidney, skeletal muscle)
In what disease states is ALT elevated in?
Liver disease (viral/toxic hepatitis, cirrhosis, hepatic obstructive disorders)
In what disease state will ALT be higher than AST?
Acute inflammatory process (like hepatitis)
In what disease state will AST be higher than ALT?
Severe liver necrosis (cirrhosis and hepatocellular carcinoma)
Why is AST higher than ALT in severe liver necrosis?
Mitochondrial AST is stored in RBCs and as scar tissue replaces living tissue, AST is released from the RBCs, leading to the elevated levels?
What is the difference between ALT and AST measurement?
Each utilize a different substrate
What are the substrates used for AST measurement?
Alpha-ketoglutarate and aspartate
What are the substrates used for ALT measurement?
Alpha-ketoglutarate and alanine
What is the name of the method used to measure ALT and AST?
Karmen method
What is actually measured in the Karmen method?
As NADH is converted to NAD, a decrease in absorbance at 340 nm is observed which is proportional to AST activity
In the measurement of AST, what enzyme is used to catalyze the conversion of oxaloacetate to malate?
Malate dehydrogenase
What does GGT stand for?
Gamma-glutamyltransferase
What reaction does GGT catalyze?
Catalyzes the transfer of a gamma-glutamyl group from a donor peptide to an acceptor compound.
What type of molecules can be acceptor of a gamma glutamyl group from a donor peptide?
Another peptide, an amino acid, or water
Where is GGT found?
Found in most cells, in the cell membrane
Where is the highest amounts of GGT found in the body?
In the kidney
Besides, the kidney, where else can GGT be found?
Liver, prostate, pancreas and brain
GGT found in the serum originates from what body system?
Hepatobiliary system
What disease is GGT elevations sensitive for?
Liver disease
Why is GGT the most sensitive out of all the liver enzymes?
It elevates first and persists longer
GGT levels can help interpret elevated levels of what enzyme?
ALP
If ALP and GGT are both elevated, what disease does this indicate?
Hepatic disease
If ALP is elevated and GGT is normal, what does this say about the source of the ALP?
Nonhepatic source, like bone disease, pregnancy or childhood bone growth
What drugs can induce GGT synthesis and elevate serum levels?
Alcohol intake, phenytoin and barbituates
What specimen is preferred for GGT analysis?
Serum or EDTA plasma
Why isn’t heparin preferred for GGT analysis?
Heparin causes turbidity in the reaction mixture and thus, interferes with the measurement
How long is the sample for GGT analysis stable at refrigerated temperature?
7 days
How long is the sample used for GGT analysis stable if frozen?
2-3 months
What is a common substrate used for GGT measurement?
Gamma-glutamyl-p-nitroanilide
What is produced when GGT reacts with gamma-glutamyl-p-nitroanilide?
p-nitroaniline is formed
What is measured in GGT analysis?
p-nitroaniline, which is yellow
