Zymosterol is located in the plasma membrane of cultured human fibroblasts

Journal Article · Fri May 25 04:00:00 EDT 1990 · Journal of Biological Chemistry; (USA)

OSTI ID:6774830

Echevarria, F; Norton, R A; Nes, W D; Lange, Y ^[1]

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1. Rush Medical College, Chicago, IL (USA)

Zymosterol (5 alpha-cholesta-8(9),24-dien-3 beta-ol) comprised a negligible fraction of the mass of sterol in cultured human fibroblasts but was well labeled biosynthetically with radioactive acetate. Treatment of cells with triparanol, a potent inhibitor of sterol delta 24-reductase, led to a marked increase in labeled zymosterol while its mass rose to 1 mol% of total sterol. All of this sterol could be chased into cholesterol. Furthermore, cell homogenates converted exogenous radiolabeled zymosterol to cholesterol. Three lines of evidence suggested that biosynthetically labeled zymosterol was associated with the plasma membrane. (1) About 80% of radiolabeled zymosterol was oxidized by the impermeant enzyme, cholesterol oxidase, in glutaraldehyde-fixed intact cells. (2) Sucrose density gradient analysis of homogenates showed that the equilibrium buoyant density profile of newly synthesized zymosterol was identical with that of the plasma membrane. (3) Newly synthesized zymosterol was transferred as readily from fixed intact fibroblasts to exogenous acceptors as was cholesterol. Given that cholesterol is synthesized within the cell, it is unclear why most of the zymosterol is in the plasma membrane. The pathway of cholesterol biosynthesis may compel zymosterol to flux through the plasma membrane. Alternatively, plasma membrane zymosterol may represent a separate pool, in equilibrium with the zymosterol in the intracellular biosynthetic pool.

• OSTI ID: 6774830
• Journal Information: Journal of Biological Chemistry; (USA), Journal Name: Journal of Biological Chemistry; (USA) Vol. 265:15; ISSN JBCHA; ISSN 0021-9258
• Country of Publication: United States
• Language: English

Related Subjects

550201* -- Biochemistry-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
ACETATES
ANIMAL CELLS
ANIMALS
BIOLOGICAL PATHWAYS
BIOSYNTHESIS
BODY
CARBOXYLIC ACID SALTS
CELL CONSTITUENTS
CELL MEMBRANES
CHOLESTEROL
CHROMATOGRAPHY
CONNECTIVE TISSUE CELLS
ENZYME INHIBITORS
ENZYMES
FIBROBLASTS
HYDROGEN COMPOUNDS
HYDROXY COMPOUNDS
ISOTOPE APPLICATIONS
LIQUID COLUMN CHROMATOGRAPHY
MAMMALS
MAN
MEMBRANE PROTEINS
MEMBRANES
METABOLISM
ORGANIC COMPOUNDS
ORGANS
OXIDOREDUCTASES
PRIMATES
PROTEINS
SEPARATION PROCESSES
SKIN
SOMATIC CELLS
STEROIDS
STEROLS
SYNTHESIS
TRACER TECHNIQUES
TRITIUM COMPOUNDS
VERTEBRATES