Clinical Enzymology
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mention the muscle enzymes
Creatine kinase Aldolase Glycogen phosphorylase
What is the function of creatine kinase (CK)?
CK catalyzes the reversible phosphorylation of creatine (Cr) by ATP.
What are the subunits of CK?
The subunits are B and M
Name the three different possible pairs of CK subunits.
BB (CK-1), MB (CK-2), MM (CK-3)
How does CK contribute to energy supply during muscle contraction?
When muscles contract, ATP is converted to ADP, and CK rephosphorylates ADP to ATP using creatine phosphate as a phosphorylation reservoir.
Write down the chemical reactions for the reversible phosphorylation at pH 9.0 and 6.7, respectively.
At pH 9.0: Cr + ATP → ADP + CrP At pH 6.7: CrP + ADP → ATP + Cr
Which ion is an obligate activating ion for CK
Mg^(2+) ion
List some metal ions that inhibit CK enzyme activity.
Mn^(2+), Ca^(2+), Zn^(2+), and Cu^(2+).
What other substances can inhibit CK activity?
Excess ADP, citrate, fluoride, nitrate, acetate, iodide, bromide, malonate, urate, and cystine.
Why is CK considered unstable?
CK is unstable due to sulfhydryl group oxidation
In which tissues is CK activity high
CK activity is high in striated muscle, heart tissue, the gastrointestinal tract, and the urinary bladder
Which parts of the body are essentially devoid of CK activity
The liver and erythrocytes.
How does Mg^2+ contribute to the CK reaction?
Mg^2+ forms complexes with ATP and ADP, acting as an obligate activating ion
explain 4 clinical significances of creatine kinase
• Serum CK activity is increased in all patients with injury, inflammation, necrosis(death of cells within an orgsn) of skeletal or heart tissue • Elevation of CK activity can be the only sign of clinical neuromascular disorders including progressive muscular dystrophy • Increased CK activity may also be present in viral myositis (inflammation of the muscles that are used to move the body), polymyositis • Serum CK iso enzyme have been used to diagnose myocardial infarction
what are the reference ranges/intervals for creatine kinase
• males: 46 - 171 U/L • females: 34 - 145
What methods are used for creatine kinase determination
Creatine kinase (CK) determination involves spectrophotometric monitoring of the conversion of NADP^+ to NADPH at 340 nm.
How is NADPH monitored in the process of creatine kinase determination?
NADPH production during the CK reaction is monitored using spectrophotometry at a wavelength of 340 nm.
What role does N-acetylcysteine play in optimizing the CK determination reaction?
N-acetylcysteine activates CK and optimizes the reaction.
Why is EDTA added to the reaction mixture during CK determination?
EDTA binds Ca^(2+) ions, stabilizing the reaction mixture and enhancing CK determination
How does Adenosine pentaphosphate (Ap5A) and AMP affect adenylate kinase during CK determination?
Ap5A and AMP inhibit adenylate kinase (AK), preventing interference in CK measurement.
Which specimens are suitable for CK analysis and why
Serum and plasma from heparinized tubes are suitable because other anticoagulants inhibit CK activity.
How does an anticoagulant other than heparin affect CK activity
Anticoagulants other than heparin reduce CK activity.
Does moderate hemolysis affect CK activity? Explain
No, moderate hemolysis does not significantly affect CK activity because red blood cells (RBCs) contain no CK.
How long can CK be stabilized at room temperature, 4°C, and −20°C respectively?
Room temperature: Stabilized for 8 hours 4°C: Stabilized for 48 hours −20°C: Stabilized for 1 month