The Influence of Natural and Model Forms of Humic Acids on the Dynamic Parameters of Model Membranes

In this paper the influence of humic acid concentrations extracted from Histosols (HA-A) and their model forms (HA-B) separated from humic substances commercially produced by Carl Roth GmbH + Co.KG on the dynamic properties of liposome membranes was determined. Differences in the quality of the humic acids (HA-A and HA-B) were determined by the 1HNMR and FTIR methods. Liposomes from the sonication of egg yolk lecithin (EYL) in an aqueous solution and synthetic Dipalmitoylphosphatidylcholine (DPPC) were used. Fluidity of liposome membranes was determined by the EPR technique with spin probes (TEMPO, 16DOIXYL). The electrical parameters of membranes were found using a Keithley 6517 electrometer. Our study showed significant differences in the influence of HA-A and HA-B on the membranes. In the bilayer membranes of the liposomes of HA-A admixture there was slightly more stiffening of the interior of the membrane in comparison to HA-B. A similar effect was observed in the surface layer of the liposome membranes. This difference is particularly evident for DPPC liposomes, however, the EYL liposomes admixture with HA-B slightly increased the fluidity of the surface layer. Electrical study confirmed this effect. The study shows that natural and model forms of humic acids differ in their effects on the activity of tested membrane models. The strong differences in the interaction of HA-A and HA-B on parameter F in DPPC liposomes can be result from the transport of humic acids connected to the metal ions inside the membranes (xenobiotics present in the environment).

Potential application of cellulase and hemicellulase assay techniques for assessing the forage quality and performance of rumen micro-organisms

Cellulose and hemicellulose are the major structural polysaccharides of plant cell wall. The efficient utilization of these polysaccharides by ruminants is often restricted by the presence of lignin. Cellulose and hemicellulose are hydrolysed by a group of enzymes called cellulases and hemicellulases. The present paper describes the cellulase and hemicellulase assay methods and their potential applications.Carboxymethyl (CM)-cellulose, Avicel, cellobiose, xylobiose, p-nitrophenyl-p β-D-glucoside (pNPG), p-nitrophenyl-β-D-cellobioside (pNPC), p-nitrophenyl-β-D-xyloside (pNPX) and p-nitrophenyl- α-L-arabinofuranoside (pNPAf) were from Sigma. Birchwood xylan and filter paper are from Carl Roth GmbH and Co., Germany and Whatman International Ltd, UK, respectively. H3P04-Swollen cellulose and 4-O-methyl-α-D-glucuronyl-xylotriose (mGpA-Xyl3) were prepared as described (Wood, 1988; Khandkeet al., 1989a).