Plasma enzymes Flashcards
what is an Enzyme?
enzymes are proteins that act act as biological catalysr, altering reaction rates and providing a means of regulating metabolic rxn?
how are plasma enzymes measured?
by their biological activity or their masses
which enzymes fulfil their physiological function in the plasma?
renin and coagulation factors
enzymes are naturally present in the plasmadue to turn over.What happens when damage to cell occurs?
there is increased amounts of enzymes willbe released and their concentrations in the blood will rise.
Not all increases of enzymes levels are due to cell damage. what are other factors?
- increase cell turnover
- cellular proliferation ( e.g. neoplasmia)
- increased enzyme synthesis ( enzyme induction)
- decreased clearance
- obstruction to secretion
Reduced plasma enzyme activity maybe caused by ?
- genetic abnormality
- reduced activity
- reduced cell production
most enzymes are removed by which cells?
reticuloendothelial cells and amylase is removed by glomeruli cells becasue the component is small enough to be filtered
plasma amylase activity rises in which diease forms?
acute renal failure, change in clearance is not as important as changes in plasma enzymes
what is an isoenzyme?
different molecular forms of proteins with the same catalyic activity. an isoenzyme may be unique to a tissue or several may be present in proportion charactistic of a tissue.
how are isoenzymes measured?
individually measured or detected by exploiting differences in their biological or physio-chemical properties.
enzyme assays usually depend on the measurement of?
measurement of catalytic activity of the enzyme, rather than the concentration of the enzyme protein itself.
why does assays for enzymes require optimised and standardised testing ot be reliable?
because each enzyme molecule can catalyse the reaction of many reactions of many molecules of substate , measurement of activity provides great sensitivity.
Disadvantages of enzyme assay
- lack of specificity to a particular tissue or cell types especiallly in diagnosis of tissue damage.
- many enzymes are common to more than one tissue, and hence if may be hard to determine where the tissue is damage.
- after a singly damage to the tissue there is a rise in the level as the ezyme is release and as the enzyme is cleared it is released. it is important to check the time the test was taken and not the result.
Many enzymes are common to more than one tissue, hence when there is an increase in enzyme it is likely that the tissue origin is not known. this problem may be obviated in two ways
- different tissues may contain two or more enzymes in different portions. e.g ASt and ALT are both release in the heart and liver cells. but ALT is more common in liver cells .
- some enzymes exist in different form such as isoenzymes. individual isoforms are often characteristic of a particular tissue, although they may have similiar catalytic activities they often differ in some other measureable property such as heat stability.
3.
There are two types of Aminotranferase. what are they?
- alanine aminotransferase
- aspartate aminotransferase
AST Is lower or higher in most cells except the liver
LOWER
Where is AST found in liver cells?
Mitochondria and cytosol
ALT is found where in liver cells?
Cytosol only
AST is released in which tissue other than the liver?
- caradiac muscle
- skelItalianpancreas
- RBC
high levels of AST and ALT are indicative of ?
severe liver damage, acute hepatitis, crush injuries and tissue hypoxia
what does ULN mean?
Upper limit of normal
In inflammatory or infective conditions, such as viral hepatitis which enzyme is higher
ALT
In inflitative disorder which liver enzyme is higher
AST because there is damage to both mitochondrial and cytoplasmi membranes .
in hepatocellular disease plasma levels of transaminases are
10- 100 times higher ULN
in uncomplicated Cholestasis (obstruction) what is the rate of of transminase
less than 10 times ULN
levels of AST to up 2x ULN without cell damage
Alcoholism
ALP means?
Alkaline Phosphatase
What is alkaline phosphatase?
a group of glycoprotein enzymes that act as a phosphotransferases by hydrolysing various types of monophosphate bond at alkaline pH.
where is ALP found?
liver, bone (osteoblast), placenta and intestinal epithelium.
Pathological increases in ALP activity are seen in?
Cholestatic liver disease and in bone diseases in which there is an increase in osteoblastic activity e.g. Paget disease and osteomalacia.
what is the level of ALP in obstructive cholestasis?
Greater than 3 times the ULN. approximately 350 ULN
hepatocelular disease the level of ALP is?
a slight increase but less than three times ULN (150 - 300)
in the liver ALP is found on two sites. which are?
- the sinusoidal surfaces of hepatocytes
- the microvilli of the bile canaliculi
The isoenzyme of ALP is found in which conditions?
- pregnancy
- growing children
Is ALP activity higher or lower in normal healthy eldery people?
Higher , thi smay reflect the high incidence of mild sub-clinical Paget’s disease in the elderly.
Is ALP increased in osteoporosis?
No, unless it there is a fracture .
ALP levels are increased in which type of tumours.
Bony and hepatic origin and seen in primary and secondary tumours.