Oswald A. Roels

The stability and structure of mixed lipid monolayers and bilayers: I. Properties of lipid and lipoprotein monolayers on OsO4 solutions and the role of cholesterol, retinol, and tocopherol in stabilizing lecithin monolayers

Lipid monolayers have been examined on OsO4-containing substrates. The results showed that OsO4 reacted only when double bonds were present in the hydrocarbon portion of monolayer molecules. No evidence for polar group interaction between saturated lecithins, monoglycerides, fatty acids, nor cholestanol and OsO4 was obtained. Egg lecithin and oleic acid monolayers were unstable after reaction with OsO4 and dissolved into the substrate. Cholesterol, monoolein, monolinolein, and d-α-tocopherol yielded stable monolayers after reaction with OsO4. Monolinolein formed a solid film at high surface pressure and all-trans-retinol gave an incompressible solid on OsO4 substrates, indicating polymer formation by cross linking via diesters of osmic acid. In contrast, monoolein formed dimers. Lung lipoportein was attacked by OsO4 and the characteristics of the film were altered. Only the protein moiety reacted. Egg lecithin was stabilized at the air-water interface in 1:1 mixed monolayers with either cholesterol, retinol, or tocopherol. Egg lecithin was stabilized at the interface by incorporation into the OsO4-retinol polymer. The results obtained with egg lecithin-cholesterol and egg lecithin-tocopherol mixed monolayers indicated that in these mixed films the reaction of OsO4 with double bonds of lecithin was inhibited. These results are discussed in terms of the staining and fixing properties of OsO4 on cell membranes and model myelinic systems.

The occurrence of vitamin A in biological membranes

Abstract 1. 1. Rats maintained on a low vitamin A intake were intraperitoneally injected with 50.7 μg [11,12- 3 H 2 ]retinyl acetate. 15 h later, the animals were killed and liver and kidney plasma membranes, kidney endoplasmic reticulum and erythrocyte ghosts were prepared. 2. 2. The labeled vitamin A content of the membrane preparations varied consistently between 0.003–0.005 μg retinol/mg N, while the level in the homogenate varied from 0.001–0.009 μg retinol/mg N. The labeled vitamin A content of the erythrocyte ghosts was low (max. 0.0001 μg retinol/mg N) probably due to heavy hemoglobin contamination. 3. 3. The radioactive vitamin A compounds were strongly bound to the membranes: n- hexane removed only 7% of the radioactive compounds, whereas chloroform-methanol (2:1, v/v) extraction of the membrane preparations removed 90% of the radioactive compounds. 4. 4. Thin-layer chromatography of the chloroform-methanol (2:1, v/v) extract of the kidney endoplasmic reticulum, in three different solvent systems, revealed that retinol and retinoic acid were the dominant forms of vitamin A. This was confirmed by combined column and thin-layer chromatography (using a fourth solvent system) of the chloroform-methanol (2:1, v/v) extract of endoplasmic reticulum.

The stability and structure of mixed lipid monolayers and bilayers: II. The effect of retinol and α-tocopherol on the structure and stability of lipid bilayers

Myelinics were prepared by dispersing ovolecithin alone, ovolecithin and retinol, ovolecithin and tocopherol, or ovolecithin and cholesterol in water. Electron microscopic observations of the negatively stained myelinics showed that retinol, tocopherol, and cholesterol decreased (in the order given) the thickness of the hydrophobic regions of the lipid bilayers and increased the mean hydrophilic layer thickness, compared to myelinics of ovolecithin alone. When OsO 4 was applied to the dried myelinics prior to negative staining, the organization of the pure ovolecithin myelinics was completely destroyed, whereas the mixed lipid myelinics resisted the destructive effect of this treatment. It is therefore suggested that retinol and α-tocopherol may influence the structure and stability of specific areas of biological membranes by their interaction with phospholipid molecules in the lipid bilayers of the membrane.

NITROGEN METABOLISM OF AQUATIC ORGANISMS. II. THE ASSIMILATION OF NITRATE, NITRITE, AND AMMONIA BY BIDDULPHIA AURITA1

Biddulphia aurita, a centric diatom, can grow on either nitrate, nitrite, or ammonia as its sole nitrogen, source.

Myelin-like configurations in ochromonas malhamensis

The nuclear region of Ochromonas malhamensis is an active site for lipid organization and production of myelin-like bodies. These bodies resemble myelin forms reported in other microorganisms and mammalian tissue. Such lipid bodies may have important implications for understanding membrane biogenesis and mechanisms whereby cells synthesize complex lipid systems. We have therefore examined naturally occurring myelinics in Ochromonas and produced synthetic myelinics in our laboratory to obtain information about the structure and composition of these lipid bodies. We have found that myelin bodies in Ochromonas malhamensis resemble myelinics produced by dispersion of egg lecithin in water. Fixation with glutaraldehyde prior to osmium tetroxide treatment protects both natural myelinics in Ochromonas malhamensis and synthetic egg lecithin myelinics; both are degraded when fixed with osmium tetroxide alone.

The influence of α-tocopherol on arylsulfatases A and B in the liver of vitamin A-deficient rats

Abstract 1. 1. The effect of different levels of dietary α-tocopherol on arylsulfatases A and B (EC 3.1.6.1) was investigated in the liver of vitamin A-deficient rats and pair-fed controls. 2. 2. Arylsulfatase A was increased in the liver of vitamin A-deficient rats receiving “normal” dietary α-tocopherol, but not when the rats were fed a high level of vitamin E. 3. 3. Arylsulfatase B was increased in vitamin A deficiency regardless of the dietary α-tocopherol level. 4. 4. Incubation at 37° of the lysosome-rich liver fraction caused more rapid release of both arylsulfatases from the lysosomes of the deficient rats receiving “normal” dietary α-tocopherol. High dietary α-tocopherol reversed this phenomenon. 5. 5. The effect of retinol added in vitro appeared to be the opposite of its effect in vivo on sulfatase release from the lysosomes, whereas α-tocopherol had the same effect when added in vitro as when fed at high levels in vivo. 6. 6. The effect of vitamin A deficiency on sulfate metabolism might be mediated through the role of retinol and perhaps of α-tocopherol on the stability of biological membranes.