Question

Q1: Say you have a patient serum sample. You follow the Lab 8 kinetic enzyme assay procedure for lactate dehydrogenase (LD) and obtain a slope of 0.0212 min^-1 at 340 nm. What is the patient's LD activity? Please show a work.

Q2: If you fall down a flight of stairs, your serum CK activity will rise for the next two days or so. Explain why the serum CK activity increases.

Activity (U/L) = (12650)(rate) One U/L activity is defined as the amount of enzyme that will catalyze the formation of one micromole (10–6 mol) of product in one minute

Answer 1

Ans. Lactate dehydrogenas plays a vital role in synthesis of ;actic acid and is characterised by reduction of puruvate to lacti acid and is charaterised by the NADH enzyme. In the enzyme assay the reduction in NADH is used to calculate the concentration.

The extinction coefficient for NADH at 340 nm would be 6220. The change in NADH concentration which means the LD activity would be calculated by Slope/extinction coefficient.

Thus LD activity = 0.0212/6220

LD activity = 3.40 * 10^-6

Serum CK is an enzyme which catalyses the phosophorylation of creatinine by ATP. Serum CK is highest in striated muscle, brain and heart tissue. When contraction of muscles occurs the rephosphorylation of ADP to ATP occurs which is catalysed by CK. It provides energy for prepaing body and contraction of muscles for fight or flight reaction.

In case of muscle trauma the levels of serum CK rises within 12 hours and last for 1 to 3 days followed by reduction in CK by cessation of muscle injury. Hence i order to prepare the body for fight or flight response, initiating muscle contraction and for cessation of muscle injury the serum CK had lasted for 2 days.