title: Biochemical characterization of a mitochondrial-like organelle from Blastocystis sp. subtype 7.
abstract: A mitochondrion-like organelle (MLO) was isolated from isotonic homogenates of Blastocystis. The organelle sedimented at 5000 g for 10 min, and had an isopycnic density in sucrose of 1.2 g ml(-1). Biochemical characterization enabled the demonstration of several key enzymes that allowed the construction of a metabolic pathway consisting of an incomplete Krebs cycle linked to the oxygen-sensitive enzymes pyruvate : NADP(+) oxidoreductase (PNO), acetate : succinate CoA transferase (ASCT) and succinate thiokinase (STK), which cumulatively are responsible for recycling CoA and generating ATP. The organelle differs from typical aerobic mitochondria in possessing an oxygen-sensitive PNO that can use FAD(+) or FMN(+) as electron acceptor but is inactive with NAD(+), Spinacia oleracea ferredoxin or Clostridium pasteurianum ferredoxin. A gene with 77 % sequence similarity to the PNO mitochondrion precursor cluster from Euglena gracilis sp[Q941N5] was identified in the Blastocystis genome database. A second cluster with 56 % sequence similarity to the pyruvate : ferredoxin oxidoreductase (PFOR) from Trichomonas vaginalis was also identified, which is in agreement with the concept that the PNO gene arose through the fusion of a eubacterial gene for PFOR with the gene for NADPH : cytochrome p450 reductase. Hydrogenase activity was not detected under the conditions used in this study. The Blastocystis oranelle therefore demonstrates significant biochemical differences from traditional mitochondria and hydrogenosomes, but possesses features of both. Based upon the results of this study, the Blastocystis organelle falls into the category of a MLO.
authors.affiliation: Haskins Laboratories, Pace University, New York, NY 10038, USA.
authors.forename: Yelena
authors.initials: Y
authors.lastname: Lantsman
authors.affiliation: Laboratory of Molecular and Cellular Parasitology and Infectious Disease Programme, Department of Microbiology, Yong Loo Lin School of Medicine, National University of Singapore, 117597, Singapore.
authors.forename: Kevin S W
authors.initials: KSW
authors.lastname: Tan
authors.affiliation: Haskins Laboratories, Pace University, New York, NY 10038, USA.
authors.forename: Mary
authors.initials: M
authors.lastname: Morada
authors.affiliation: Department of Chemistry and Physical Sciences, Pace University, New York, NY 10038, USA.|Haskins Laboratories, Pace University, New York, NY 10038, USA.
authors.forename: Nigel
authors.initials: N
authors.lastname: Yarlett