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Biochemistry Takehome Quiz #3

These notes were posted friends-only until the night before the assignment is due.

Q1: The Commish: Please go to http://www.chem.qmul.ac.uk/iubmb/ and find these, and provide a 1-2 sentence description of each enzyme's function.

Phosphoglycerate kinase is a phosphotransferase with a carboxy group as acceptor. It uses ATP and is part of the calvin cycle of carbon fixation. {EC, ATP + 3-phospho-D-glycerate = ADP + 3-phospho-D-glyceroyl phosphate} is L-lactate dehydrogenase aka lactic acid dehydrogenase. It participates in glycolysis, gluconeogenesis, and cysteine, propanoate and pyruvate metabolism. {Reaction: (S)-lactate + NAD+ = pyruvate + NADH + H+} With NAD+ or NADP+ as acceptor

alkaline phosphatase is EC, a phosphoric monoester hydrolase with wide specificity. Also catalyses transphosphorylations. The human placental enzyme is a zinc protein. {Reaction: phosphate monoester + H2O = an alcohol + phosphate} Magnesium & zinc cofactors.

cathepsin G is a chymotrypsin-like proteinase; neutral proteinase, and has specificity similar to chymotrypsin C. It is found in azurophil granules of polymorphonuclear leukocytes. {aka: EC, EC 3.4.21 are Serine endopeptidases} the 4 makes it a lyase, more specifically it is carbonate dehydratase, so it takes apart H2CO3 = CO2 + H2O, moving in the opposite direction from carbonic anhydrase.. It has a zinc cofactor and is important in nitrogen metabolism.

Q2: Loose your Inhibitions: Graph 3 sets of kinetic data given for an enzyme. Set 1: no inhibitor. Set 2: inhibitor A. Set 3: Inhibitor B. Determine Vmax and Km for the enzyme, and determine the type of inhibition and the Ki for each inhibitor.

Q3: The ol' Vmax just aint what she used to be: Draw a hypothetical Lineweaver-Burk plot for a non-competitive inhibitor in which the Km is unaffected but the Vmax shows reduced catalytic efficiency in the presence of the inhibitor.

Q4: Breathe Deeply: For carbonic anhydrase, which catalyzes the hydration of CO2: Given the Vnil and the concentration of CO2, determine the a) Vmax b) Kcat, c) catalytic efficiency (Kcat/Km) of the enzyme, and d) does it approach "catalytic perfection"? (I bet the answer is yes, and it turns out I was right: the Kcat is far larger than the Km so the reaction proceeds without hindrance once the initial association is made between enzyme and substrate.)



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