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Unformatted text preview: w know that Ced-3 is the prototype of a
family of more than a dozen proteases, known as caspases because they
have cysteine (C) residues at their active sites and cleave after aspartic acid
(Asp) residues in their substrate proteins. The caspases are the ultimate
effectors or executioners of programmed cell death, bringing about the
events of apoptosis by cleaving more than 100 different cell target proteins
(Figure 17.4). One key target of the caspases is an inhibitor of a DNase,
which when activated is responsible for fragmentation of nuclear DNA. In
addition, caspases cleave nuclear lamins, leading to fragmentation of the
nucleus; cytoskeletal proteins, leading to disruption of the cytoskeleton,
membrane blebbing, and cell fragmentation; and Golgi matrix proteins,
leading to fragmentation of the Golgi apparatus. The translocation of phosphatidylserine to the cell surface is also dependent on caspases, although
the caspase target(s) responsible for this plasma membrane alteration have
not yet been identified. Apopt...
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