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Intracellular beta-carotene transport in bovine liver and intestine is not mediated by cytosolic proteins.

The mechanisms responsible for the movement of absorbed carotenoids between intracellular organelles and for the incorporation of carotenoids into serum lipoproteins are unknown. It was the objective of this study to use bovine liver and intestine as a model to study the possible cytosolic protein-mediated carotenoid transfer between liposomes and mitochondria in vitro. Liposomes containing beta-[3H]carotene were incubated with isolated bovine hepatic mitochondria (1 mg protein) and various quantities of liver cytosol or intestinal mucosal cell cytosol (0-6 mg protein) for up to 1 h at 37 degrees C. The beta-[3H]carotene activity in liposomes was then measured over time to determine percent transfer of beta-carotene to mitochondria. Over the time period studied, the rate of beta-carotene transfer was unaffected by increasing levels of either hepatic or intestinal cytosolic protein. These results suggest that unlike many other lipid species, intracellular transport of beta-carotene is not mediated by cytosolic transport proteins and must occur by other mechanisms such as vesicular transport or by membrane-bound proteins.