Effects of lignin content on the properties of lignocellulose-based biocomposites

The paper is focused on the analysis of the behaviour of biocomposites (biodegradable composites) which are reinforced with different fillers fractions, with varying lignin contents. These materials have been carried-out by extrusion and injection moulding. The matrix, an aromatic copolyester (polybutylene adipate-co-terephthalate), is biodegradable. The lignocellulose fillers are a by-product of an industrial fractionation process of wheat straw. From the raw agro-material and by lignin extractions, various fillers fractions have been obtained by varying the fractionation conditions, both on the liquid media (aqueous or organic) and on the temperature. The fillers lignin contents vary from 30 to 14 wt% with a resultant increase of the cellulose content. We have analysed the impact of the different extraction conditions on the fillers surface and size distribution, and also on the final thermal and mechanical properties of the biocomposites. These materials present significant differences of behaviour which can fulfil some requirements for applications, such as non-food packaging or other short-lived applications (agriculture, sport …) where long-lasting polymers are not entirely adequate.     

The in vitro effects of opines and other compounds on DNAs originating from bacteria, and from healthy and tumorous plant tissues

Purified total DNAs were isolated from oncogenic or nononcogenic Agrobacterium tumefaciens cells as well as from normal and crown gall tissues. Opines (octopine, nopaline, lysopine), plant hormone (auxin IAA) and some carcinogenic compounds were used in order to correlate their effects on in vitro strand separation and synthesis of DNAs with in vivo tumorous cell multiplication. Octopine (or nopaline) induced chain opening of DNAs originating from octopine (or nopaline)-metabolizing bacteria and from same bacteria strain-induced tumorous cells. This phenomenon was measured by the increase in DNA hyperchromicity which is concentration dependent. The tested compounds stimulated the in vitro synthesis of the same DNAs. Under the same conditions, in vitro strand separation and synthesis of healthy plant DNA was not (or only slightly) enhanced, except in the case of particular hormone-connected healthy cell DNA. IAA and carcinogens stimulated in vitro synthesis and induced in vitro strand separation (dose-dependent effect) of DNAs isolated from crown gall cells and inducing bacteria. Compared to healthy cell DNAs, these DNAs were thus susceptible to structurally very diversified molecules and in this way behave as do mammalian tissue DNAs. The opine and IAA actions observed here were specific for plant tissue DNA; cancerous human or animal tissue DNAs were insensitive. By their presence in the crown gall cells, opines possibly maintain destabilized areas (required for rapid growth and division) on tumor cell DNA. The cooperative actions of IAA and opines as well as small RNA and RNA fragments on gene activation, might explain the autonomy of plant tumor cells.     

Lipid peroxidation in purified plasma membrane fractions of rat liver in relation to the hepatoxicity of carbon tetrachloride

Preparations of rat liver sinusoidal plasma membrane have been tested for their ability to metabolize the hepatotoxin carbon tetrachloride (CCl4) to reactive free radicals in vitro and compared in this respect with standard preparations of rat liver microsomes. The sinusoidal plasma membranes were relatively free of endoplasmic reticulum-associated activities such as the enzymes of the cytochrome P450 system and glucose-6-phosphatase. CCl4 metabolism was measured as (i) covalent binding of [14C]-CCl4 to membrane protein, (ii) electron spin resonance spin-trapping of CCl3. radicals and (iii) CCl4-induced lipid peroxidation. By all of these tests, purified sinusoidal plasma membranes were found unable to metabolize CCl4. The fatty acid composition of the plasma membranes was almost identical to that of the microsomal preparation and both membrane fractions exhibited similar rates of the lipid peroxidation that was stimulated non-enzymically by gamma-radiation or incubation with ascorbate and iron. The absence of CCl4-induced lipid peroxidation in the plasma membranes seems to be due, therefore, to an absence of CCl4 activation rather than an inherent resistance to lipid peroxidation. We conclude that damage to the hepatocyte plasma membrane during CCl4 intoxication is not due to a significant local activation of CCl4 to CCl3. within that membrane.     

Kinetic studies of a beta-lactamase by a computerized microacidimetric method.

On-line computerized treatment of enzyme kinetic data allows the precise measurement of Michaelis--Menten constants (Km and V) from a single progress curve. This method has been used to determine the kinetic constants of a beta-lactamase extracted from an Escherichia coli strain. In the profile of enzymatic activity there obtained, Km and V are a function of the pH. From these results some information is derived about the mechanism of the enzyme--substrate binding.