Guy M. McKhann

CHARACTERIZATION OF SULPHATIDE-CONTAINING LIPOPROTEINS IN RAT BRAIN

—(1) Water‐soluble [35S]sulphatide is found in the 105,000 g supernatant (SN) of rat brain after intraperitoneal injection of Na235SO4. This labelled sulphatide has a density between those of free lipid and free protein.

STUDIES OF WATER SOLUBLE LIPOPROTEINS IN RAT BRAIN

—The occurrencc of water soluble lipoprotein in the 105,000 g supernatant of rat brain homogenate has been demonstrated.

Synthesis of sulphatide-containing lipoproteins in rat brain.

Abstract— 1 Puromycin inhibits [14C]leucine Hincorporation into brain proteins, but has no effect on the incorporation of [35S]sulphate into sulphatide. These effects of puromycin are observed not only with the proteins and sulphatide of whole brain, but also with the protein and sulphatide portion of water‐soluble lipoprotein complexes. 2 Microsomes can be separated into three subfractions which differ chemically, morphologically and metabolically. Protein synthesis and sulphatide synthesis are located in different submicrosomal fractions. 3 The addition of water‐soluble brain proteins to the incubation medium causes release of newly synthesized [35S]sulphatide and formation of soluble sulphatide protein complexes. One acceptor protein is identified as the lipoprotein previously shown to bind [35S]sulphatide in vivo (Herschkowitz, McKhann, Saxena and Shooter, 1968b). 4 These results suggest that protein and sulphatide synthesis can function independently and that association of newly synthesized lipid to preformed protein is possible.

The effect of nerve growth factor (NGF) on the synthesis of gangliosides.

—Dorsal root ganglia from 8‐day‐ and 14‐day‐old chick embryos contained gangliosides with a pattern qualitatively similar to that of embryonic chick brain. The pattern of gangliosides from dorsal root ganglia changed with age, there being a decrease in polysialogangliosides with increasing age. When isolated, dorsal root ganglia were incubated in the presence of a concentration of nerve growth factor (NGF) sufficient to promote the outgrowth of nerve fibres, there was increased incorporation of d‐[1‐14C]glucosamine into gangliosides. There was, however, no difference in the pattern of incorporation into gangliosides by control ganglia and those exposed to NGF.

92 Mechanism of Myelin Formation During Development

Myelin is formed by a satellite cell which wraps around the axon to form a continuous spiral of membrane. This membrane has a distinctive lipid and protein composition when compared with other membran ous structures. The myelin components may be synthesized at the level of the forming membrane, or transported into the membrane following synthesis by some other intracellular organelle.The synthesis of sulfatide, a membrane lipid, by 95 and 17-day-old rats was determined after a single intraperitoneal injection of 35S-sulfate into the sulfatide of whole brain, myelin, non-myelin organelles, and 105,000 × g supernatant of brain was followed. At times when there was no further de novo synthesis of lipid, the amount of labelled sulfatide in myelin continued to increase while that of non-myelin membranes decreased. The transfer of sulfatide from non-myelin structures to myelin appeared to be mediated by soluble lipoproteins which were isolated from supernatant, characterized, and found to contain labelled sulfatide.In vitro studies, indicated that isolated myelin contained galactocerebroside sulfokinase, the enzyme involved in the synthesis of sulfatides. Thus, isolated myelin contains some membranous components capable of synthesizing myelin lipids.These studies suggest that a lipid component of myelin is both transported into the forming membrane by a carrier lipprotein and synthesized by the myelin membrane. The relationship between these two mechanisms of formation of myelin components during development will be discussed. (SPR)