Components of sterol biosynthesis assembled on the oxygen-avid hemoglobin of Ascaris.
The parasitic nematode Ascaris infests a billion people worldwide. Much of its proliferative success is due to prodigious egg production, up to 10(6) sterol-replete eggs per day. Sterol synthesis requires molecular oxygen for squalene epoxidation, yet oxygen is scarce in the intestinal folds the worms inhabit. Ascaris has an oxygen-avid hemoglobin in the perienteric fluid that bathes its reproductive organs. Purified hemoglobin contained tightly bound squalene and functioned as an NADPH-dependent, ferrihemoprotein reductase. All components of the squalene epoxidation reaction--squalene, oxygen, NADPH, and NADPH-dependent reductase--are assembled on the hemoglobin. This molecule may thus function in sterol biosynthesis.
Sherman
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Department of Medicine, Washington University School of Medicine, St. Louis, MO.
Guinn
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B
Perdok
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Goldberg
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DE
D000818:Animals; D001200:Ascaris / Q000378:metabolism*; D006454:Hemoglobins / Q000378:metabolism*; D007700:Kinetics; D013058:Mass Spectrometry; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D010108:Oxyhemoglobins / Q000378:metabolism*; D013185:Squalene / Q000378:metabolism; D013261:Sterols / Q000096:biosynthesis* / Q000302:isolation & purification
D006454:Hemoglobins; D010108:Oxyhemoglobins; D013261:Sterols; D013185:Squalene; D009251:NADPH-Ferrihemoprotein Reductase