Description
IntroductionCreatine Kinase (CK) is primarily found in tissues such as the heart, muscle, and brain. It reversibly catalyzes the transphosphorylation reaction between creatine and ATP, playing a vital role in energy transfer, muscle contraction, and ATP regeneration. It is a crucial clinical indicator for diagnosing heart and brain diseases.Assay PrincipleCK catalyzes the conversion of Phosphocreatine and ADP to Creatine and ATP. Hexokinase then catalyzes the reaction of ATP with Glucose to form Glucose-6-Phosphate (G6P). Subsequently, Glucose-6-Phosphate Dehydrogenase (G6PDH) catalyzes the oxidation of G6P with NADP⁺ to generate NADPH, leading to an increase in absorbance at 340 nm.Component50TStorageExtraction Buffer60 mL2-8℃Reagent 11EA2-8℃. Store in the dark.Reagent 215 mL2-8℃Reagent 1: Powder in one bottle. Store at 4°C protected from light. Dissolve in 15 mL distilled water before use.Working Solution: Prepare immediately before use by mixing the dissolved Reagent 1 and Reagent 2 at a 1:1 ratio. Incubate the Working Solution at 37°C for 2 minutes prior to use.Required Materials and Equipment (Not Provided)Balance, refrigerated centrifuge, constant temperature water bath, UV spectrophotometer, 1 ml quartz cuvette, and distilled water.Crude Enzyme Extraction:Tissue Samples: Homogenize the tissue on ice in Extraction Buffer at a ratio of 1:5-10 (w/v) (e.g., weigh ~0.1g tissue, add 1 mL Extraction Buffer). Centrifuge the homogenate at 10,000 g, 4°C for 15 min. Collect the supernatant and keep it on ice for assay.Serum Samples: Assay directly.Assay Procedure:Preheat the UV spectrophotometer for at least 30 minutes. Set the wavelength to 340 nm. Zero the instrument with distilled water.In a 1 ml quartz cuvette, add:200 µl sample300 µl distilled water500 µl pre-warmed (37°C) Working SolutionMix thoroughly and immediately record the initial absorbance (A₁) at 340 nm. Record the absorbance again (A₂) after exactly 1 minute at 37°C. Calculate ΔA = A₂ - A₁.CK Enzyme Activity Calculation:General Parameters:ε (NADPH molar extinction coefficient) = 6220 L/mol/cmd (Cuvette light path) = 1.0 cmVₜₒₜₐₗ (Total reaction volume) = 1.0 mL (1000 µL)Vₛₐₘₚₗₑ (Sample volume in reaction) = 0.2 mL (200 µL)T (Reaction time) = 1 minCpr (Sample protein concentration, mg/mL)W (Sample mass, g)Vₛₐₘₚₗₑₜₒₜₐₗ (Total extract volume) = Assumed 1 mL for tissue calculations1. Based on Tissue Protein Content:Definition: One unit of activity is defined as the amount of enzyme that generates 1 nmol of NADPH per minute per mg of protein at 37°C, pH 7.0.Calculation:CK Activity (nmol/min/mg prot) = [ΔA / (ε × d)] × Vₜₒₜₐₗ ÷ (Vₛₐₘₚₗₑ × Cpr) ÷ TSimplified Formula: CK (nmol/min/mg prot) = 804 × ΔA ÷ Cpr2. Based on Tissue Sample Mass:Definition: One unit of activity is defined as the amount of enzyme that generates 1 nmol of NADPH per minute per gram of fresh tissue at 37°C, pH 7.0.Calculation:CK Activity (nmol/min/g fresh weight) = [ΔA / (ε × d)] × Vₜₒₜₐₗ ÷ (Vₛₐₘₚₗₑ / Vₛₐₘₚₗₑₜₒₜₐₗ × W) ÷ TSimplified Formula: CK (nmol/min/g fresh weight) = 804 × ΔA ÷ W3. Based on Serum:Definition: One unit of activity is defined as the amount of enzyme that generates 1 nmol of NADPH per minute per liter of serum at 37°C, pH 7.0.Calculation:CK Activity (nmol/min/L) = [ΔA / (ε × d)] × Vₜₒₜₐₗ ÷ Vₛₐₘₚₗₑ ÷ TSimplified Formula: CK (nmol/min/L) = 804 × ΔANotesBefore the formal assay, it is essential to perform a pilot test with 2-3 samples expected to have significant differences in activity.The prepared Working Solution is stable at 4°C for 7 days. However, it is recommended to use it as soon as possible after preparation.CK in serum is unstable. Determine the activity as soon as possible after sample collection. It can be stored protected from light at 4°C for up to 24 hours.Sample protein content needs to be determined separately. A BCA Protein Assay Kit can be used for this purpose.If the absorbance value (ΔA) is greater than 0.5, dilute the sample appropriately with Extraction Buffer and account for the dilution factor (D) in the calculation formulas (e.g., 804 × ΔA × D ÷ Cpr)