(15) AST - LIVER ENZYMES

Question 1

AST aka

Answer 1

Serum Glutamic-Oxaloacetic transaminase (SGOT)

Question 2

Action: Transfers amino group between aspartate & α-keto acids

• Involved in the synthesis (anabolism) & degradation (catabolism) of AA.
• Widely distributed, highest activities in cardiac, liver & skeletal muscle

Answer 2

AST

Question 3

2 isoenzymes of AST

Answer 3

o Cytoplasmic AST
o Mitochondrial AST

Question 4

released when there’s severe cell damage

Answer 4

Mitochondrial AST

Question 5

▪ predominant AST isoenzyme in serum
▪ Released when cell membrane has injury

Answer 5

Cytoplasmic AST

Question 6

NOTE:

AST Diagnostic significance

Answer 6

o Fxn: Useful in assessing chronic progressive dszs
▪ AST isn’t liver-specific

o After acute MI, AST levels begin to rise in 6-8hrs, peak at 24hrs, & return to normal in 5 days.

o Also ↑ in hepatocellular & skeletal muscle dis.
▪ AST is greatly released in chronic liver disorders w/ progressive damage to hepatocytes.

Question 7

Assay for enzyme activity:

o Karmen method:

Answer 7

o Karmen method:

▪ Coupling / 2ndary / indicator enzyme: Malate Dehydrogenase
* Coupling enzyme is an Oxidoreductase kemerut
▪ Monitors ↓ in absorbance @340nm → colorless product
* Product: Form of coenzyme is oxidized
▪ Falsely ↑ in hemolyzed sample

Question 8

NOTE:

Answer 8

• MD isn’t part of the serum, since it is a coupling enzyme, it came from the reagent used to measure AST
• AST activity is directly proportional w/ the product of MD.