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Unformatted text preview: points total)
A researcher studying a protein with one cysteine residue wasn’t sure if it was functionally important or not.
She wanted to ‘block’ the cysteine by reacting it with iodoacetamide (I-CH2CONH2). The reaction occurs only
when the sidechain of the cysteine is deprotonated, and displaces the iodide, making a bond to the CH2 of the
acetamide. She checked her old textbook and found that a typical pKA value for cysteine is 8.3 at 25° C, and
identiﬁed a simple colorimetric assay to determine the extent to which the cysteine was modiﬁed. Her reading
also reminded her that protonation/deprotonation reactions are usually very rapid. v( • v( Q5. A. (6 points)
Write a kinetic scheme and corresponding differential equation that describes the rate of formation of modiﬁed
protein with time as a function of the concentration of protein and acetamide present in the solution, and any
other needed parameters. Q5. B. (9 points, 3 for each part)
Doing a test reaction with 1 µM protein and 10 µM acetamide at pH 6, she found that only 10% of the protein
had reacted over a 1 hour period. She looked up a similar reaction and...
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- Fall '09