Numbers of proteins colliding with the surface of the [membrane] sphere each second

Range actin monomers ~8,000, Arp2/3 complex 500, capping protein 300, cofilin 15,000 sec^-1
Organism Fission yeast Schizosaccharomyces pombe
Reference Berro J, Sirotkin V, Pollard TD. Mathematical modeling of endocytic actin patch kinetics in fission yeast: disassembly requires release of actin filament fragments. Mol Biol Cell. 2010 Aug 15 21(16):2905-15. doi: 10.1091/mbc.E10-06-0494. p.2912 right columnPubMed ID20587776
Method "...if [researchers] approximate the geometry of the membrane where polymerization occurs as a sphere of radius r=25 nm, a minimum value for the flux of proteins reaching its surface can be estimated from the diffusion equation as 4pDArCmax, where D is the diffusion coefficient, A is Avogadro’s number, and Cmax is the bulk concentration of each protein. If [researchers] use a low estimate for D=2µm^2/sec in a crowded environment, the following numbers of proteins collide with the surface of the sphere each second: ~8000 actin monomers, 500 Arp2/3 complexes, 300 capping proteins, and 15,000 cofilins. In the worst case, this is 2–30 times more than the numbers of proteins consumed in the reactions. Thus [researchers'] assumption regarding diffusion is valid even if crowding reduces diffusion up to one order of magnitude. However, this is unlikely, because [they] estimate that the actin network occupies <3% of the volume of the patch. This idea agrees well with estimates of diffusion and actin assembly in similar actin networks (Plastino et al., 2004 Rafelski et al., 2009)."
Entered by Uri M
ID 111097