Cytochalasin B binding by human platelets

✍ Scribed by C. Richard Zobel; Chan Y. Jung

• Publisher: John Wiley and Sons
• Year: 1982
• Tongue: English
• Weight: 436 KB
• Volume: 113
• Category: Article
• ISSN: 0021-9541
• DOI: 10.1002/jcp.1041130221

✦ Synopsis

intact human platelets bind cytochalasin B (CB) with a capacity of 100-120 p mols CBimg protein or approximately 7 x lo4 rnoleculeslcell and dissociation constants (KD) ranging from 2 x 10" to lo6 M. Up to 85% of this saturable binding is displaced by 'lo+ M cytochalasin E (CE). This CE-sensitive binding also appears heterogeneous with K, similar to those of the overall binding. The CE-insensitive binding, however, appears as a single component with K , G 4 x lo-' M. The sedimentable constituents from frozen, thawed, and washed cells also bind CB with K, ranging from 2.4 x lO-'to 1.5 x lo-' M and a total capacity of approximately 39 p molslmg protein which accounts for only 4% of the ligand binding lo the intact cell. The major portion (60-80%) of this CB binding is displaceable by 500 m M D-glucose and has a K , of 1.5 x M, while only 10-15% is CE-sensitive with a KD of 2.4 x lo-' M. It is concluded that 95% of the saturable CB binding in platelets is associated with the cytosol of which 80-85% is sensitive to CE and that only 3% of the cellular binding is glucose senGtive, membrane-associated binding. If the CE-sensitive binding associated with the cytosol is entirely to actin, the stoichiometty of this binding is approximately one CB to 30 actin monomers, which is greater by an order of magnitude than that for CB binding to muscle actin.