Isolation and characterization of dolichols from Tetrahymena pyriformis

Dolichol levels during development and ageing of Drosophila melanogaster

1. Dolichol levels in the fruit fly, Drosophila melanogaster were determined at the larva and pupa stages and in 1, 10, 20 and 30-day-old flies. 2. Free dolichol increased from 1.2 micrograms/g wet weight in the larvae to 14.9 micrograms/g in 30-day-old flies, while total dolichol increased from 3.4 micrograms/g in the larvae to 21.2 micrograms/g at 30-days-old. 3. Dolichol released after saponification is primarily from dolichyl fatty acid ester, which accounts for up to 65% of the total dolichol. 4. The major dolichol homologs, which remain relatively constant throughout development and ageing in D. melanogaster, are C-80, C-85 and C-90, which represent approximately 7%, 60% and 33%, respectively.

Dolichol in human brain: regional and developmental aspects

Distinct regional differences in dolichol content were defined in human brain from 15 to 76 years of age. Concerning the regional distribution of dolichol, levels were: higher in cortical gray matter than in subcortical white matter, highest among cortical regions in temporal gray matter, highest among all brain regions in thalamus, and lowest among all brain regions in lower brain stem and spinal cord. The developmental changes in the contents of dolichol were found to be different among brain regions. For example, among regions with the highest levels of dolichol, in thalamus there was a six to sevenfold increase, but in parietal gray matter, only a 2.5-fold increase. Regional and developmental changes in the proportions of the individual molecular species (isoprenologues) of dolichol were also observed. The findings indicate that the metabolism of dolichol is not uniform among regions of developing and aging human brain and may have implications for the role of dolichol in normal and diseased human brain.

Distribution, metabolism and function of dolichol and polyprenols

Polyisoprenoid alcohols consisting of 9 or more isoprene units are present in all living cells. They can be fully unsaturated (polyprenols) or alpha-saturated (dolichol). Dolichol forms may have additional saturation at or near the omega-end. Some species contain ony dolichol or only polyprenols while others have nearly equal amounts of both types. Some polyisoprenoid alcohols consist entirely of trans isoprene units but most, including dolichol, contain both trans and cis units. Considerable advances in lipid methodology have occurred since the first review of polyisoprenoid alcohols by Hemming in 1974. For example, direct analysis of both dolichol and Dol-P by HPLC has replaced earlier methods which were often both insensitive and inaccurate. The availability of radiolabeled dolichol and polyprenols has facilitated studies concerning the metabolism and distribution of these compounds. Those studies suggest that only a small portion of the dolichol present in cells is likely to be involved in glycosylation. Polyisoprenoid alcohols are usually present at a family of homologues where each differs in size by one isoprene unit. Little or no size related specificity has been observed for any reaction involving dolichol or polyisoprenol intermediates. The overall length of polyisoprenoid alcohols may, however, affect the manner in which these compounds influence the physical and biochemical properties of membranes. Studies on the biosynthetic pathway leading from cis, trans Pol-PP by phosphatase action. The formation of the dolichol backbone from a polyprenol requires the action of an additional enzyme, an alpha-saturase. This enzyme does not always act at the level of a single common substrate, since Pol-PP, Pol-P, and polyprenol all appear to be utilized as substrates. The major product of the de novo pathway differs among different species. Dol-P would appear to be the most energy efficient end-product since it can participate directly in glycoprotein formation. Most often, however, Dol-P is not the major product of metabolic labeling experiments. In some cases, dolichol is formed so that rephosphorylation is required to provide Dol-P for participation in glycoprotein formation. The kinase responsible for this phosphorylation appears to bypass the considerable stores of dolichol present in tissues (i.e. sea urchin eggs) in favor of dolichol derived directly from de novo synthesis. Although HMGR is a major regulatory component of the pathway leading to polyisoprenoid alcohols and cholesterol, control is most often not co-ordinated.(ABSTRACT TRUNCATED AT 400 WORDS)

Dolichol deposition in developing mammalian brain: content of free and fatty-acylated dolichol and proportion of specific isoprenologues

Dolichol serves a critical role in N-linked glycoprotein synthesis as the carrier of saccharide moieties. In this study the deposition of dolichol was investigated in developing rat brain. The contents of both the free and fatty-acylated forms of dolichol as well as the specific isoprenologues of dolichol were determined. Two distinctive phases of rapid dolichol deposition were observed; the first during brain development, and the second, with aging. The predominant form of brain dolichol was shown to be the free derivative at all ages; however, during the two phases of rapid deposition of total dolichol, fatty-acylated dolichol became detectable and increased transiently. The rapid rate of increase of brain dolichol during development occurred later than that of brain cholesterol, which shares a common biosynthetic pathway with dolichol. Thus, the peak rate of increase of dolichol occurred at 25 days postnatal, and of cholesterol, at 18 days postnatal. A distinct ontogenetic alteration in the proportion of the individual molecular species (isoprenologues) of dolichol also was defined. These observations suggest that dolichol is particularly involved in developmental events of the third to sixth postnatal weeks in rat brain, e.g. myelination and synaptogenesis.

Dolichyl phosphate phosphatase from Tetrahymena pyriformis

A soluble dolichyl phosphate phosphatase from Tetrahymena pyriformis was purified about 68-fold. The enzyme appeared to be specific for dolichyl phosphate and existed in two interrelated forms, one of mol.wt. about 500000 and the other of mol.wt. about 63000. The enzyme was strongly inhibited by 5 mM-Mn2+ and was strongly stimulated by Mg2+. Tetrahymena in the exponential growth phase contained more of this enzymic activity than cells in stationary or lag phase. The dolichyl phosphate phosphatase may be loosely bound to mitochondrial membranes. Two roles proposed for this enzyme are (1) that of releasing dolichol from its phosphorylated biosynthetic form for its use in the cell as unesterified dolichol or dolichyl ester and/or (2) that of regulation of synthesis of glycoproteins or some other glycosylated compound.