Physico-chemical changes in tomato with modified atmosphere storage and UV treatment.

Physico-chemical changes in ripe tomato (Lycopersicon esculentum Mill.) were analyzed on day 0 and 2 weeks after ultraviolet-C (UV-C) light treatment or modified atmosphere (MA) storage and combined UV-C + MA storage at 10 °C. Modified atmosphere packaging (MAP) film was used to create MA conditions. The tomatoes were evaluated for surface colour, mass loss, firmness, respiration rate, total soluble solids and antioxidant capacity. The tomatoes treated with UV-C and MA storage underwent least changes in their physico-chemical properties, indicating that combination of UV-C and MA storage was successful in retaining the attributes of the fresh product. The increase in antioxidant capacity of the tomatoes during UV-C treatment suggested that UV treatment during post harvest handling may be successfully combined with MA storage, resulting in a product with better nutritive value.

A revised fluorometric assay for Gaucher's disease using conduritol-beta-epoxide with liver as the source of Beta-glucosidase.

To date, enzymatic diagnosis of Gaucher's disease via a fluorometric assay procedure which utilizes 4-methylumbelliferyl-beta-D-glucopyranoside as a substrate has not been possible when liver serves as the source of enzyme since currently employed fluorometric procedures cannot adequately differentiate between a broad-specificity beta-glucosidase and lysosomal glucocerebrosidase activities in crude extracts of liver. Incorporation of conduritol-beta-epoxide into the incubation medium for the fluorometric assay allows one to selectively measure the glucocerebrosidase activity present in a given liver extract. In five cases of Gaucher's disease this revised fluorometric procedure proved as effective as the assy procedure which utilizes authentic, radiolabeled glucocerebroside as the substrate in demonstrating a deficiency of glucocerebrosidase activity in liver.

Analogs of ceramide that inhibit glucocerebroside synthetase in mouse brain.

In a search for potent inhibitors of glucocerebroside biosynthesis, we synthesized aromatic analogs of the enzyme's substrate, ceramide, many of which have not previously been described in the literature. Mouse brain and spleen, rat brain, and human placenta and spleen were all found to be susceptible to inhibition by a variety of compounds, although to differing extents. The most potent inhibitor was 2-decanoylamino-3-morpholino-1-phenylpropanol. The dehydro version of this compound (2-decanoylamino-3-morpholinopropiophenone) was less effective but it produced inactivation of the enzyme, probably by covalent reaction with the enzyme's active site. Examination of the various effects seen leads us to suggest that the active region of the enzyme contains four recognitional sites: an anionic moiety that may bind the glucose in activated form, an oxygen-binding region oriented toward the third carbon atom of ceramide, a narrow region that binds the alkyl chain of the fatty acid moiety, and a less narrow region that binds the hydrocarbon chain of the sphingoid base moiety.

Conversion by rat brain preparation of lignoceric acid to ceramides and cerebrosides containing both alpha-hydroxy and nonhydroxy fatty acids. Effects of compounds which affect sphingolipid metabolism.

Three synthetic compounds which affect sphingolipid metabolism in vitro were examined for their effects on the synthesis in a rat brain system of nonhydroxyceramide, hydroxyceramide, nonhydroxycerebroside, and hydroxycerebroside from [1-14C]ignoceric acid. These compounds are N-octanoyl-D-threo-p-nitrophenylaminopropanediol (Compound I), N-(2,3-epoxydecanoyl)-norephedrine (Compound II), and N-decyl-N'-glucosylthiourea (Compound III). In the presence of up to 0.5 mM Compound I, only the hydroxyceramide fromation increased, while the synthesis of the other three lipids decreased. Compound II strongly inhibited the formation of all four lipids at all concentrations tested (0.1 to 1 mM). Compound III increased the synthesis of both ceramides approximately 2-fold at 1 mM, but the conversion of lignoceric acid to both cerebrosides remained relatively unchanged. Several significant conclusions from these observations are discussed.

Short chain ceramides as substrates for glucocerebroside synthetase. Differences between liver and brain enzymes.

In order to increase the sensitivity of the assay for ceramide: UDPGlc glucosyltransferase, the enzyme that makes glucocerebroside, we synthesized a variety of ceramide homologues that might be better substrates than the naturally occurring ceramides. N-Octanoyl sphingosine proved to be the best lipid tested in liver and brain. It could be added to the tissue homogenate in the dry form, as a thin layer coated on Celite, or in liposomes, prepared from lecithin and cerebroside sulfate. The liposomal form produced better replication of assay values. It is suggested that the addition of cerebroside sulfate to liposomal preparations might be a good, and more physiological, replacement for the commonly used dicetyl phosphate. A new homologue of DL-sphinganine, decasphinganine, was synthesized by an efficient series of steps and acylated with different fatty acids to form ceramide homologues. The best substrate in this series was the lauroyl amide and it is suggested that this lipid be used in cerebroside synthetase assays because of the convenience of preparing it, even though it is not as good as octanoyl sphingosine. Both compounds are distinctly better than natural ceramide or DL-sphinganine amides. From comparisons of enzyme activity under various conditions, the tentative conclusion is drawn that the enzymes in liver and brain have different properties, and that liver has two different synthetases.