Effect of fatty acids and monoglycerides on permeability of lipid bilayer

The effect of fatty acids and monoglycerides on barrier properties of liposomal membranes prepared from egg phosphatidylcholine was investigated. The incorporation of these lipids as liposomal membrane components induced the alteration of the permeability to less permeable liposomally entrapped drugs, sulfanilic acid and procainamide ethobromide (PAEB). Monoolein caused greatly increased permeability of both drugs and unsaturated fatty acids markedly enhanced the release rate of PAEB, while saturated fatty acids caused a small increase in the release rate.Electron spin resonance (ESR) investigation with 5-nitroxide stearic acid showed that fatty acids disordered the hydrophobic region of the lipid bilayer and the disordering effect of unsaturated fatty acids was greater than that of saturated ones. It was demonstrated that the incorporated fatty acids and monoglycerides interacted with the polar region of the membranes by ESR study with cholestane label and ¹H-NMR study. These results indicated that the increase in the membrane permeability caused by fatty acids and monoglycerides associated with the disorder in the membranes' interior and the interaction of the incorporated lipid with the polar head group of phospholipid.     

Hereditary respiration deficiency in Saccharomycodes ludwigii

Saccharomycodes ludwigii, supposed to be petite-negative, gave rise to respiration-deficient mutants when acriflavine and ultraviolet irradiation, respectively, were applied to this yeast, strain IFO 1194. The frequency of such mutants was very low as compared with that in Saccharomyces cerevisiae and other petite-positive yeasts. Cytochrome composition was characterized by spectrophotometry at the temperature of liquid nitrogen. The respiratory mutants examined contained cytochrome c unaltered in quality and quantity. Cytochrome b was often present only in small amounts though never absent, while cytochrome a+a₃ was either present or absent. The respiratory mutants could form zygotes after conjugation with a wild-type culture of opposite mating type ( vs. a). The hybridization and segregation analysis of spore tetrads showed the inheritance of respiratory mutant character to be either Mendelian or non-Mendelian and similar to that of pet (nuclear) and rho^- (cytoplasmic) mutants, respectively, in Saccharomyces cerevisiae.     

Freeze-thaw stability of starches from different botanical sources: Correlation with structural features

Native starches from twenty-six botanical sources were determined for their structural features and stability against freeze-thaw treatments. Starch gels (5%, w/w) were prepared and repeatedly freeze-thawed up to five cycles by storing at −18 °C for 21 h and then at 30 °C for 3 h. Water release (syneresis) from the thawed gel after the 1st, 3rd and 5th cycle was measured gravimetrically, and evaluated in relation to apparent amylose content (AAC) and distribution of amylopectin branch chains with degree of polymerization 6-12 (APC ratio). Syneresis was not observed for starch gels of cassava, normal and waxy japonica rice up to the 1st, 3rd and 5th cycle, respectively. On the other hand, syneresis rapidly occurred for starch gels of elephant yam, new cocoyam, potato, edible canna, and water yam. Optimal multiple linear regression models were generated to predict individual effect of AAC and APC ratio on syneresis of starch gels. The prediction models illustrated the positive unit-contribution of AAC and negative unit-contribution of APC ratio to syneresis (P < 0.001).     

Stabilization of quaternary structure and activity of bovine liver catalase through encapsulation in liposomes

Bovine liver catalase was encapsulated in an aqueous phase of the phospholipid vesicle (liposome) to improve the stability of its tetrameric structure and activity. The catalase-containing liposomes (CALs) prepared were 30, 50 and 100 nm in mean diameters (CAL₃₀, CAL₅₀ and CAL₁₀₀, respectively). The CAL₁₀₀ included the types I, II and III based on the amounts of catalase encapsulated. The CAL₃₀, CAL₅₀ and CAL₁₀₀-I contained one catalase molecule per liposome, and the CAL₁₀₀-II and CAL₁₀₀-III on average 5.2 and 17 molecules, respectively. The storage stability of catalase in either CAL system was significantly increased compared to that of free catalase at 4 °C in a buffer of pH 7.4. At 55 °C, free catalase was much more deactivated especially with decreasing its concentration predominantly due to enhanced dissociation of catalase into subunits while it was so done at excessively high enzyme concentration mainly due to enhanced formation of catalase intermolecular aggregates. Among the three types of CAL₁₀₀, the CAL₁₀₀-II showed the highest thermal stability, indicating that an excess amount of catalase in the CAL₁₀₀-III was also disadvantageous to maintain an active form of the catalase even in liposome. In the CAL₁₀₀-III, however, the stability of catalase was significantly improved compared to that of free catalase at the same concentration. The CAL thermal stability was little affected by the liposome size as observed in the CAL₃₀, CAL₅₀ and CAL₁₀₀-I. An intrinsic tryptophan fluorescence of the catalase recovered from the CAL₁₀₀-II thermally treated at 55 °C revealed that a partially denatured catalase molecule was stabilized through its hydrophobic interaction with liposome membrane. This interaction depressed not only dissociation of catalase into subunits but also formation of an inactive intermolecular aggregate between the catalase molecules in a liposome. Furthermore, either type of CAL₁₀₀ showed a higher stability than free catalase in the successive decompositions of 10 mM H₂O₂ at 25 °C mainly because the H₂O₂ concentration was kept low inside liposomes due to the permeation barrier of the lipid membrane to H₂O₂.     

Transformation of Polyoxins D,E, and F with Sodium Bisulfite

Polyoxins D, E, and F which possess 5-carboxyuracil as the nucleobase were reacted selectively with sodium bisulfite at pH 4.0 resulting in facile decarboxylation to afford corresponding 5,6-dihydrouracil-6-sulfonates and uracil type polyoxins (polyoxins L, M, and K) in good yield. The former compounds were also converted to the latter almost quantitatively with mild alkali treatment. Biological activities of the transformed compounds were described.