During endocytosis, membrane components move to intraluminal vesicles of the endolysosomal compartment for digestion. At the late endosomes, cholesterol is sorted out mainly by two sterol-binding proteins, Niemann-Pick protein type C (NPC)1 and NPC2. To study the NPC2-mediated intervesicular cholesterol transfer, we developed a liposomal assay system. (Abdul-Hammed, M., B. Breiden, M. A. Adebayo, J. O. Babalola, G. Schwarzmann, and K. Sandhoff. 2010. Role of endosomal membrane lipids and NPC2 in cholesterol transfer and membrane fusion. J. Lipid Res. 51: 1747–1760.) Anionic lipids stimulate cholesterol transfer between liposomes while SM inhibits it, even in the presence of anionic bis(monoacylglycero)phosphate (BMP). Preincubation of vesicles containing SM with acid sphingomyelinase (ASM) (SM phosphodiesterase, EC 3.1.4.12) results in hydrolysis of SM to ceramide (Cer), which enhances cholesterol transfer. Besides SM, ASM also cleaves liposomal phosphatidylcholine. Anionic phospholipids derived from the plasma membrane (phosphatidylglycerol and phosphatidic acid) stimulate SM and phosphatidylcholine hydrolysis by ASM more effectively than BMP, which is generated during endocytosis. ASM-mediated hydrolysis of liposomal SM was also stimulated by incorporation of diacylglycerol (DAG), Cer, and free fatty acids into the liposomal membranes. Conversely, phosphatidylcholine hydrolysis was inhibited by incorporation of cholesterol, Cer, DAG, monoacylglycerol, and fatty acids. Our data suggest that SM degradation by ASM is required for physiological secretion of cholesterol from the late endosomal compartment, and is a key regulator of endolysosomal lipid digestion.

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This study highlights the potential use of yellow Zea mays seed chaff (YZMSC) biomass as a biosorbent for the removal of Cr 3+ , Cd 2+ and Pb 2+ ions from aqueous solutions. Fourier transformed Infrared analysis of the biomass suggests that YZMSC biomass is basically composed of cellulose and methyl cellulose. The biosorption capacities, qmax, of YZMSC biomass for Cr 3+ , Cd 2+ and Pb 2+ are 14.68, 121.95 and 384.62 mg/g respectively. Biosorption equilibrium was achieved at 20, 30 and 60 min for Cr 3+ , Cd 2+ and Pb 2+ respectively. YZMSC biomass was found to have higher biosorption capacity and overall kinetic rate of uptake for Pb 2+ than for Cd 2+ and Cr 3+ . However, Cr 3+ had better initial kinetic rate of uptake by the biomass than Pb 2+ and Cd 2+ . The Freundlich equilibrium isotherm model was found to describe equilibrium data better than Langmuir model suggesting that biosorption of these metal ions could be on more than one active site on the surface of YZMSC biomass. Kinetic study predicted the pseudosecond kinetic model as being able to better describe kinetic data obtained than either modified pseudo-first order or Bangham kinetic models. Biosorption of Cr 3+ , Cd 2+ and Pb 2+ onto YZMSC biomass was endothermic in nature with large positive entropy values. Biosorption of these metal ions onto YZMSC biomass was observed to be feasible and spontaneous above 283 K. Optimization of biomass weight for the removal of these metal ions suggest that 384 kg, 129 kg and 144 kg of YZMSC biomass is required for the removal of 95% of Cr 3+ , Cd 2+ and Pb 2+ metal ions respectively from 100 mg/L of metal ions in 10 tonnes of aqueous solutions.

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