Enzymes

Question 1

How do changes in plasma enzyme activity come about?

Answer 1

Increases in rate of release of enzymes into blood

- some normally present due to normal cell turnover

Question 2

What causes changes in plasma activity?

Answer 2

Necrosis or severe damage to cells
Increased rate of cell turnover
Cellular proliferation - Neoplasia
Increased concentrations of enzymes within cells (eg increased synthesis - induction)
Duct obstruction

Question 3

What is the half-life of plasma cholinesterase?

Answer 3

12-14 days

Question 4

What is the half-life of Lactate Dehydrogenase?

Answer 4

6.8 days

Question 5

What is the half-life of Alanine transaminase?

Answer 5

6.3 days

Question 6

What is the half-life of Aspartate transaminase?

Answer 6

2.0 days

Question 7

What is the half-life of Creatine Kinase?

Answer 7

1.4 days

Question 8

How is enzyme activity measured?

Answer 8

Usually with spectrophotometry: use of substrate or product which is coloured/absorbs specific wavelength(s): usually automated.

Question 9

How are enzyme activity units given?

Answer 9

Usually given in terms of catalytic activity

May be given as concentration (amount of enzyme protein/unit volume e.g. mg/l) - may be proportional to catalytic activity

International Unit (IU) of enzyme activity: amount of enzyme catalyzing conversion of 1mmol substrate to product per minute (i.e. mmol/min): may be more complex where multiple substrates involved

Reference values defined by individual labs
since reaction conditions may vary