Nucleotide exchange between cytosolic ATP and F-actin-bound ADP may be a major energy-utilizing process in unstimulated platelets.
About 40% of the cytosolic ADP of human platelets is tightly bound to protein and the complex is precipitated from the cells by 43% ethanol. We show here that this ADP is bound to F-actin by three criteria (a) copurification with F-actin, (b) specific extraction with water and (c) by specific interaction with DNase I. Platelets contain 0.3 mumol/10(11) cells of this F-actin--ADP complex compared to the total actin content of 0.8 mumol/10(11) cells, which is consistent with the view that actin is maintained in different pools (F-actin--ADP, profilactin, G-actin). In intact platelets the F-actin-bound ADP turns over rapidly and we have determined a turnover rate at 37 degrees C of 0.1 +/- 0.025 s-1 by using a double-labelling procedure. This rapid turnover indicates that F-actin in intact platelets is in a very dynamic state, which may be necessary for rapid responses to stimuli. If it is assumed that the source of the ADP bound to F-actin is cytosolic ATP, the turnover of F-actin ADP measured represents an ATP-consuming process that would account for up to 50% of total ATP consumption in resting platelets.
Daniel
J L
JL
Molish
I R
IR
Robkin
L
L
Holmsen
H
H
D000199:Actins / Q000097:blood* / Q000302:isolation & purification; D000244:Adenosine Diphosphate / Q000097:blood* / Q000302:isolation & purification; D000255:Adenosine Triphosphate / Q000097:blood*; D001792:Blood Platelets / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism*; D004734:Energy Metabolism; D000431:Ethanol; D006801:Humans; D008956:Models, Chemical; D011485:Protein Binding; D012995:Solubility; D014867:Water
D000199:Actins; D014867:Water; D000431:Ethanol; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate