Phospholipid Acyl Chain Length Research Articles

Sterol efflux from mammalian cells induced by human serum albumin-phospholipid complexes. Dependence on phospholipid acyl chain length, degree of saturation, and net charge.

Human serum albumin and phospholipids can interact to cause a synergistic sterol release from mammalian cells in tissue culture. In the presence of the complexes formed between albumin and saturated phosphatidylcholine, release was twice as great as that which occurred with the unsaturated phospholipid complexes. Within the saturated series, sterol release increased with chain length until the number of carbon atoms in the acyl group was 18, after which sterol release decreased. In the unsaturated series, sterol release decreased as the number of double bonds increased. Branching of the acyl chain, or analogues with the polar group in the sn-2 position reduced sterol efflux. In the presence of human serum albumin, maximal sterol efflux occurred with phospholipids having two adjacent acyl chains and zero net charge; sterol release decreased as net charge increased.

The elongation of exogenous fatty acids and the control of phospholipid acyl chain length in Micrococcus cryophilus.

The synthesis of fatty acids de novo from acetate and the elongation of exogenous satuated fatty acids (C12-C18) by the psychrophilic bacterium Micrococcus cryophilus (A.T.C.C. 15174) grown at 1 or 20 degrees C was investigated. M. cryophilus normally contains only C16 and C18 acyl chains in its phospholipids, and the C18/C16 ratio is altered by changes in growth temperature. The bacterium was shown to regulate strictly its phospholipid acyl chain length and to be capable of directly elongating myristate and palmitate, and possibly laurate, to a mixture of C16 and C18 acyl chains. Retroconversion of stearate into palmitate also occurred. Fatty acid elongation could be distinguished from fatty acid synthesis de novo by the greater sensitivity of fatty acid elongation to inhibition by NaAsO2 under conditions when the supply of ATP and reduced nicotinamide nucleotides was not limiting. It is suggested that phospholipid acyl chain length may be controlled by a membrane-bound elongase enzyme, which interconverts C16 and C18 fatty acids via a C14 intermediate; the activity of the enzyme could be regulated by membrane lipid fluidity.