Clinically Important Enzymes

1. Alanine amino transferase (ALT)

• Formerly known as glutamic pyruvate transaminase.
• It is an enzyme necessary for energy production, it is present in a number of tissues including the liver, heart and skeletal muscles, but is found in the highest concentration in the liver.
• Because of this, it is used in conjunction with other liver enzymes to detect liver diseases, especially hepatitis or cirrhosis without jaundice.
• Additionally in conjunction with the aspartate aminotransferase test (AST),it helps to distinguish between heart damage and liver tissue damage.
• Catalyse the reversible transamination of Ɣ – alanine and 2- oxoglutarate to pyruvate and Ɣ- glutamate .
• Co factor = pyridoxal -5 phoshapte.
• Found in cytoplasm of hepatocytes and also in mitochondria. #In dogs and cats in case of Hepatocellular injury

2. Aspartate aminotransferase (AST)

• Formerly known as SGOT (Serum Glutamic oxaloacetic transaminase).
• Catalyse the transamination of Ɣ-aspartate and 2-oxoglutarate to oxaloacetate glutamate. #AST activity is relatively high more in skeletal and cardiac muscle.
• Used in equine and food animal medicine for screening of injury to hepatocytes and myocytes , but cannot differentiate between hepatocyte or myocyte injury.
• Serum AST has a longer half-life than Ck ,therefore expected to have increased diagnostic sensitivity during recovery from myocyte or hepatocytic injury.
• Importance in case of acute & chronic liver injury, Damage to kidney, pancreas, skeletal muscle, Rbc. (in Domestic animals).

3. Sorbitol Dehydrogenase (SDH)

• Also known as Iditol Dehydrogenase. # Catalyse the reaction

Sorbitol + NAD+ <——– > Fructose + NADH

• Serum SDH activity is of greater value than Serum AST activity in large animals because of increased specify for hepatocellular injury.
• Less favoured in dogs and cats for detection of hepatic injury than ALT activity because of its short half-life and labile nature.
• Located in cytoplasm.

4. Glutamate Dehydrogenase (GDH)

• It is a Mitochondrial enzyme.
• Catalyse the removal of Ɣ-glutamate to form corresponding ketimine acid, that undergo spontaneous hydrolysis to 2-osoglutamate.
• Serum GDH activity is used most commonly in food animals and horses and its level increases in hepatocellular damage particularly in hepatic necrosis.
• GDH is released only with irreversible cell injury because of its location within mitochondria.
• Importance in case of Hepatic necrosis, Bile duct obstruction, also during the time of parturation (sheep ,cattle)

5. Gamma Glutamyl transferase (GGT)

• Sometimes called gamma -glutamyl transpeptidase(GGPT).
• In gamma glutamyl cycle,catalyse the transfer of gamaglutamyl groups from gamma glutamyl peptides.
• It is an enzyme that is compared with ALP levels to distinguish between skeletal disease and liver disease.
• Because GGT is not increased in bone disorders,as is ALP, a normal GGT with an elevated ALP would indicate bone disease.
• Serum GGT activity is useful clinical indicator of cholestasis in horses and cattle because of relatively high liver GGT activity compared to dogs and cat
• Level increases in longterm liver damage.
• Importance in case of disease of hepatobilary system, associated with cholestasis and Renal injury (cattle, sheep, goat, horse)

6. Alkaline phoshatase (ALP)

• Hydrolyse a range of monophosphate & pyrophosphate at alkaline pH as well as at physiological pH.
• ALP activity has lowest specificity of routinely used liver enzymes as a result of its complexity associated with induction of different isoenzymes.
• Distinct serum ALP isoenzymes can be extracted from some of these tissues in each species eg;- Bone (B-ALP),Liver (L-ALP), and glucocorticoid induced (G-ALP)isoenzymes in canine serum.
• Importance in case of acute & chronic injury to liver, cholangitis extrahepatic bile duct obstruction.
• Elevates in normal growing animals ( dog, cat, horse)

7. Lipase

• Hydrolyse triglyceride at 1;3 positions leaving a monoglyceride.
• Serum lipase have been used classically for the diagnosis of acute pancreatits in dogs. # Has longer half-life than amylase.
• Not a useful indicator of pancreatitis in cats.
• To diagnose pancreas disease in dogs

8. Amylase

• Cleaves the alpha-D-glycon linkage of starch and glycogen.
• Level increases in acute pancreatitis and also in chronic renal dysfunction in dogs. # Importance in case of diagnosing pancreatitis in dogs & cats.

9. Creatinine Kinase (CK)

• Catalyse the exchange of phosphate moiety between creatinine phosphate and ATP. # It is the classic muscle enzyme.
• Even a small amount of muscle damage such as bruising or IM injections can result in high ck levels.
• Creatinine level increases due to renal dysfunction, blocked urethra and ruptured bladder. # Animals with high muscle mass have high-normal creatinine conc and those with low muscle mass have low creatinine conc.
• Importance in case of Acute pancreatitis in case of dogs and cats.

10. Trypsin

• Serine proteinase enzyme produced by pancreas in form of proenzyme trypsinogen. Pancreas secretes trypsinogen into intestine where it is converted by enterokinase to trypsin.

Reference

1. Clinical biochemistry of domestic animals (J.Jerry kaneko, John. Wharvey, Michael. L. bruss)