Which one of the following enzymes is predominantly mitochondrial?
Ans. is 'a' i.e., SGOT* Serum Glutamate Pyruvate Transaminase (SGPT) or Alanine Transaminase (ALT) and Serum Glutamate Oxaloacetate Transaminase (SGOT) or Aspartate Transaminase (AST) are sensitive markers of hepatocellular injury. As estimating bilirubin is a measure of functional ability of liver, it takes some time for the levels of bilirubin to increase. Enzyme levels rapidly rise because any damaged hepatocyte's membrane permeability is increased.* ALT or SGPT is purely a cytoplasmic enzyme, whereas AST or SGOT is present in both cytoplasm and mitochondria. The cytoplasmic isoform of the enzyme ASTI is derived from RBC and Heart. The mitochondrial isoform of the enzyme AST2 is derived from liver.* Hence following hepatocellular injury, the cytoplasmic enzyme ALT level rises faster (Normal level of ALT is <34 IU/L in females and <52 in males) than AST (Normal level of AST is (6 to 34IU/L in females and 8 to 40 IU/L in males). Thus AST is neither a sensitive nor a specific marker of hepatocellular damage (Not specific because it is expressed by heart as well and hence levels are elevated even after myocardial damage)* Generally when AST and ALT are elevated, AST/ALT ratio will be less than 2. If it is more than 2 it is suggestive of mitochondrial damage like alcoholic hepatitis or toxic liver injury* 5'-nucleotidase is an enzyme which catalyzes the phosphorylytic cleavage of 5'nucleotides. There are membrane bound forms and soluble forms. Membrane bound forms are GPI anchored to the cell membrane. Soluble forms are in cytoplasm. Following biliary obstruction, the bile stays in the intrahepatic biliary canaliculi. Tijs causes dissolution of liver parenchymal cell membrane and the cell bound membranes get released into circulation through hepatic sinusoids. Hence 5' nucleotidase level in circulation increases following bile duct obstruction. So, levels of 5' nucleotidase elevation along with elevation of Alkaline phosphatase confirms that the elevation of ALP is of hepatic origin (BILIARY DUCT OBSTRUCTION) not osseous (AS ALP LEVEL IS ALSO INCTREASED IN BONE RELATED CONDITIONS WITH ELEVATED OSTEOBLASTIC ACTIVITY)* Same is the case with Gamma Glutamyl Transferase. It is involved in liver conjugation reactions and absorption of neutral aminoacid along intestinal membranes. This enzyme is also a membrane bound enzyme. Hence levels are elevated following duct obstruction. But as the enzyme is involved in detoxification reactions, the enzyme gets induced by alcohol. Hence levels of GGT is high after intake of alcohol. Isolated elevation of GGT is suggestive of alcoholism. If GGT elevation is accompanied by an elevation of ALP and 5; nucleotidase, it is obstruction.
SGOT
SGPT
GGT
5' nucleotidase
Enzymes