Figure 4: Structure, ATP content and ATP hydrolysis of microparticles

Abstract

Microparticles (MPs) were obtained from a suspension of RBCs infected by P. falciparum (i-MP) or from a control suspension of RBCs (c-MP). C) Production of MPs MPs were purified by differential centrifugation of cell culture medium. Production of MPs was quantified by the Bradford assay and expressed as mg protein per mL of cell culture. RBCs were cultured for 24 hours before purification. Results are means ± SEM (N=3-6) (* p<0.05). D) Intraparticular ATP The extramicroparticular ATP concentration (eATPMP) was determined in a suspension of MPs by on-line luminometry. The value of intraparticular ATP was derived after permeabilization of MPs with digitonin (arrow, 50 µg/mL). Values are expressed as nM/mg protein of both, i-MPs and c-MPs, from which the intraparticular ATP content could be derived (QiATP MP, inset D). QiATP MP, i.e., the ratio between [eATPMP] at 1 min post-digitonin and basal [eATPMP], is expressed as means ± SEM (N=3-6). E) ATP hydrolysis of MPs A suspension of MPs was exposed to exogenous ATP (50-1800 nM). The time course of eATP concentration ([eATP]) was quantified by on-line luminometry. The initial rate of [eATP] decay after ATP addition was measured from kinetics curves (data not shown). Values are expressed as nM ATP/(min mg MPs). Results are means ± SEM (N=2-3, n=4-6). The dotted line is a fit of a linear function to experimental data, with slope of the curve KATP: 0.33 ± 0.02 (min mg)-1.R2:0.97 for c-MP and KATP:1.08 ± 0.06 (min mg)-1 R2:0.98 for i-MP. The asterisk represents the result of an independent experiment where ATPase activity was determined by following the time course of [32P]Pi released from [γ-32P]ATP at 900 nM (N=2, n=2). * for c-MP and * for i-MP.