Biochemistry enzyme kinetics lab report

Alkaline phosphatases are enzymes that are typically membrane-bound glycoproteins that catalyze the hydrolytic cleavage of monoesters at basic pH levels2. This enzyme is found in most advanced level eukaryotes and prokaryotes. When the hydrolysis of the monophosphate ester takes place at the basic pH levels an inorganic phosphate is released2. The enzyme can remove phosphate groups from several different types of molecules such as alkaloids, proteins, or nucleotides. In humans’ alkaline phosphatases play critical roles in the growth and development of teeth and bones, however, it can be found it other parts of the body such as in the liver and kidneys3. The phosphatases are essential for mineralization in humans to allow calcium and phosphorus to be deposited in bones and teeth3. The enzyme was reacted with 4-nitrophenyl phosphate as the substrate1. 4-nitrophenyl phosphate does not resemble a protein and is a non-specific substrate commonly used to assay alkaline phosphatases4. When the alkaline phosphatase performs hydrolysis on 4-nitrophenyl phosphate a highly colored phosphate free product is given1,4. This reaction releases the phosphate group on 4-nitrophenyl phosphate to give the product 4-nitrophenolate which has a molar absorptivity at 405nm under basic conditions with an extinction co-efficient of 18.8x103 M-1cm-1 1,4.

To experiment the effects of inhibition on the enzyme the inhibitor phenylalanine at 75mM and Na2HPO4 at 15mM was also used. Inhibition of enzymes may be carried out via irreversible pathways that work through covalent bonds or through reversible pathways. Reversible pathways include a competitive inhibition where the inhibitor binds to the active site of the enzyme or through a noncompetitive pathway where the enzyme binds to a side other than the active site, which may subsequently change the shape or conformation of the active site6. When a phosphate group PO43- is removed by hydrolysis from an organic compound it is referred to as dephosphorylation. This is the reaction in which the phosphatases operate. The reaction is important in a physiological setting because it enables the activation or deactivation of enzymes by removal of phosphoric esters; a prime example is the conversation of adenosine triphosphate to adenosine diphosphate through phosphorylation7.

The Michaelis-Menten kinetics model is used in biochemistry as a model for enzyme kinetics. The model uses an equation to explain the rate of the enzymatic reactions that occur . It does this by relating the reaction rate, Velocity or Vmax, to the substrate concentration, [S]. Vmax describes the constant values for each enzyme-substrate complex with the theoretical maximum velocity of the enzyme to turn over products at maximum saturation of the substrate concentration6. The Km value, known as the Michaelis constant, is the dissociation constant of the enzyme-substrate complex and measures the enzyme-substrate affinity6. Low Km values equate to a higher affinity of the enzyme-substrate6. The Michalis constant equal to the substrate concentration at half of the Vmax value6. The model best describes single substrate single substrate kinetics with an assumption that the back reaction of enzyme plus product being negligible6.

Inhibitors effect both the Vmax and Km values according to the type of inhibition produced on the enzyme or enzyme-substrate. Irreversible inhibitors create permanent inhibition through covalent bonds6. Reversible inhibitors work through intermolecular forces. Competitive inhibition prevents the substrate from binding active site of the enzyme, the Km appears to increase, and the Vmax does not change6. Noncompetitive inhibitors bind to any site other than the active site allowing for the enzyme-substrate complex to still form, no change to the Km, a decrease to the Vmax, with the enzyme conformational change restricting activity6. For each of these models a disassociation constant value of Ki can be calculated and is analogous to the Km for a substrate6. The Beer-Lambert Law, , is applied to determine what the concentration is in these biomolecules after samples have been prepared and analyzed through a platereader by measuring the attenuation of light8. The absorbance, or attenuation of light, is reliant on two assumptions, the value ‘A’ is directly proportional to the concentration ‘C’ and is also directly proportional to the light path ‘L’8. ‘E’ is a constant that is referred to as the molar extinction coefficient and is used to measure the probability of the electron transition8.