Problem: Cell Cycle
At the start of mitosis, sister chromatids are held together by a complex of proteins. Separase is an enzymes that cleaves the complex, enabling the choromatids to separate during mitosis. Separase is overexpressed in many cancer cells, and scientists hypothesized that they might be able to slow or stop the growth of cancer cells by blocking the activity of separase. The scientists found a compound they named Sepin-1 that appears to effectively cleave and thus inactivate purified separase protein in vitro (in a test tube).
• In normal cells, separase is kept in an inactive state until it is needed. Explain how the progression of cells past sequential cell cycle checkpoints and the activity of enzymes such as separase is controlled by interactions between two major groups of regulatory proteins.