quiz 2 review ( enzymes)
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What are isoenzymes?
Groups of related enzymes that have the same active site (can catalyze the same reaction) but have different properties
What does Q10 value refer to?
Q10 = difference in enzyme activity or reaction rate when performed at 2 temperature differing by 10oC. The rate of most enzyme-catalyzed reactions will double for an increase of 10oC
What does Km refer to in an enzyme catalyzed reaction?
Michaelis constant - the substrate concentration at ½ maximum velocity (rate). It is determined to ensure that the substrate concentration used is 10 - 100 times the Km. (to ensure zero order kinetics)
What does stereochemical specificity mean and give one example.
Enzymes that only catalyze reactions of one enantiomeric form of a substrate. i.e. either D or L form. Example: LD will only react with L-Lactate
What is the difference between an activator and a coenzyme?
Both are cofactors. An activator is inorganic. A coenzyme is organic
What does the term specificity mean in relation to enzyme catalyzed reactions?
That enzymes will only catalyze reactions of a specific substrate (or bond) or a small number of substrates (or bonds)
What is an I.U.?
The quantity of an enzyme that will catalyze the reaction of 1 μmol of substrate per minute per L (or mL) of serum. Written as IU/L or mIU/mL
Explain the two general approaches used to measure the extent of an enzymatic reaction
• Fixed-time (endpoint) 2. Continuous monitoring (rate or kinetic)
Describe the type of reaction that a hydrolase catalyzes
Catalyzes breakdown of substrate by the addition of H2O
Why do we monitor the activity of an enzyme catalyzed reaction during zero-order kinetics?
Because we want the reaction rate to only depend upon the enzyme concentration. Then enzyme activity is proportional to enzyme concentration
What is the principle of the BLB method for measuring ALP?
p-nitrophenylphosphate + H2O −→−Mg2+ALP p-nitrophenol + inorganic phosphate Alkaline buffer = AMP (amino methyl propanol) Optimum pH = 9 - 10
In the BLB method, what is the purpose of serum blanks and how are they produced?
Produced by acidifying the reaction mixture. Acid converts the p-nitrophenol from yellow to colorless. Allows a correction for the color of serum
Which type of liver disease produces the highest levels of ALP in plasma or serum?
Extrahepatic obstruction
The highest levels of ALP are seen in which type of bone disease?
Paget’s Disease (bone resorption)
If Alkaline Phosphatase (ALP) and Acid Phosphatase (ACP) catalyze the same general type of reactions, what is the main difference between the two enzymes?
Their optimal pH. ALP - pH 9 - 10 ACP - pH 4.9 - 5.0
Why are the BLB and Roy et al. methods for acid phosphatase (ACP) not preferred methods in a continuous monitoring system?
Because their products, p-nitrophenol (BLB) and thymolphthalein (Roy et al.), were colorless at the acid pH used. So the Hillman method is used because its product (α-napthol phosphate) gives a color.
Why would a hemolyzed sample not be used for measurement of acid phosphatase (ACP)?
There is a high level of ACP in red blood cells.
What is PAP?
Prostatic Acid Phosphatase - the isoenzyme that originates from the prostate
Older methods employ tartrate as a means of differentiating prostatic ACP (PAP). What is an alternate approach?
Use the methods of either Hillman or Roy et al. PAP hydrolyzes these substrates more readily than nonprostatic isoenzymes of ACP, so any reaction is due to PAP
Very high elevations of acid phosphatase (ACP) are seen in which clinical condition?
Metastatic prostate cancer So it is most useful to confirm metastatic prostate cancer and to stage prostate cancer.
What is PSA and what is its clinical utility?
PSA = prostate specific antigen Clinical use - monitoring of treatment for patients with known prostatic carcinoma. Also used in diagnosis along with rectal exam and ultrasound.
Why is human amylase called alpha-amylase?
It hydrolyzes α 1,4-glucosidic linkages of polyglucans.
Why were defined substrate methods introduced to measure amylase?
Because of problems with older starch based methods. i.e. variability of starch substrate and inconsistency of hydrolysis conditions.
How can amylase be measured by O2 consumption?
Starch −→−−−−− (Amylase) maltose, maltotriose →GlucoseGlucose + O2 −→−−−−−−−−(Gluose, Oxidase) H2O2 + gluconolactone Decrease in O2 measured.