Solution

ID: past-exam-of-the-biochemistry-course-of-the-university-of-cambridge/2024/paper-5/section-2/f/solution

ToxB strongly reduces sedimentable wild-type actin, whereas act1-117 shows little additional reduction from its already low baseline. Wild-type actin is mainly in the pellet without drug and mainly in the supernatant with drug. Using the approximate bar heights, the pelleted fraction changes from to . Thus the drug suppresses polymer accumulation but does not eliminate the measured pellet entirely.
For act1-117, the pellet is only about one-third of the recovered signal even without drug, and remains near that fraction with drug: approximately and . The mutant is therefore relatively resistant to the drug's further effect under this assay, but it is not a wild-type-quality polymerizer with an unchanged high polymer mass. These are approximate within-pair fractions; unequal total recoveries and loading limit precise quantitative comparison. sedimentation also requires confirmation that pellet material is filamentous rather than aggregated.

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