Role of the reticuloendothelial system in the catabolism of low density lipoprotein in the rat

The role of the reticuloendothelial system (RES) in receptor-independent catabolism of human low density lipoprotein (h-LDL) was evaluated in the rat in vivo after blockade of its phagocytic activity with gadolinium chloride (GaCl3). After blockade of the RES with GaCl3, the recovery of [125I] h-LDL in the liver of 17 alpha-ethinyl oestradiol-treated rats (EE-rats), was decreased by 37 and 16%, 15 and 60 min after h-LDL injection, respectively. This decrease did not result in a decreased LDL degradation which represented 14 and 55% of the injected dose in the two groups of rats after 15 and 60 min respectively, both on GaCl3 and control rats. Contrasting with EE-rats, the catabolism of h-LDL in untreated rats is much slower and takes place essentially through a receptor-independent mechanism. Six hours after the injection of [125I] h-LDL, 64% of the dose was degraded. This proportion decreased to 45% after blockade of the RES phagocytic activity. This 30 percent difference represents the proportion of h-LDL catabolized by receptor-independent mechanisms present in the Küpffer and endothelial cells. We conclude from our study that in the normal rat, the parenchymal cells of the liver on the one hand and the Küpffer and endothelial cells on the other hand contribute 70 and 30% respectively to the receptor-independent catabolism of low density lipoproteins in vivo.     

Isolation of apical plasma membrane in rabbit gallbladder epithelium by Percoll density gradient centrifugation

The apical membranes of rabbit gallbladder epithelial cells were isolated by treating the homogenate with Ca2+ or Mg2+ and centrifuging the suspension in Percoll gradient. In this way brush-border membranes were obtained with enrichment factors ranging between 10 and 20 and yields of 15-30%. A second method is described with which membranes were isolated, without any preliminary treatment, first by differential centrifugation, then with Percoll gradient; the final membrane enrichment was over 15, however the yield was very low (3%). Many possible enzymatic markers of the apical plasma membrane were investigated: L-gamma-glutamyltransferase, alkaline phosphatase, leucine aminopeptidase, sucrase. The first appears to be that of choice. Apical membrane fraction could be also evidenced by autofluorescence or by labeling with Lotus tetragonolobus lectin. Preliminary experiments showed that apical plasma membranes isolated in this way form vesicles.     

Application of extended Kalman filter to identification of enzymatic deactivation

A recursive estimation scheme, the Extended Kalman Filter (EKF) technique, was applied to study enzymatic deactivation in the enzymatic hydrolysis of pretreated cellulose using a model previously developed by the authors. When no deactivation model was assumed, the results showed no variation with time for all the model parameters except for the maximum rate of cellobiose-to-glucose conversion (r'(m)).The r'(m) variation occurred in two zones with a grace period. A new model of enzymatic hydrolysis of pretreated cellulose deactivation was proposed and validated showing better behavior than the old deactivation model. This approach allows one to study enzyme deactivation without additional experiments and within operational conditions.     

Mathematical modelization of a packed-bed reactor performance with immobilized yeast for ethanol fermentation

The performance of a continuous vertical packed-bed reactor with yeast immobilized in carrageenan gel beads is reported. The study focuses on the mathematical modelling of the steady-state fermentor behavior by means of a tanks-in-series model which includes the intrinsic kinetic model and the external mass transfer and internal diffusion-reaction conditions in the beads.     

Observations on the germinability in vitro of pollen from Camellia japonica L. (Theaceae)

Pollen grains from samples of Camellia japonica living in soil (A) and in greenhouse (B) were collected daily from just-opened anthers. The pollen was sown in various liquid media and incubated at 28 C. Higher germinative ability of A in comparison with B was observed and related to the relative humidity which is higher in soil than in greenhouse. This phenomenon recurs even if the composition of the culture medium is changed. However the composition of the medium greatly influences the percentage of germination of both A and B notwithstanding the environmental conditions. The pollen collected from anthers dehiscing in the first day of the anthesis has a high germinative ability which suddenly decreases in the ripe pollen of the following days.     

Trivalent behavior during prophase I in male mice heterozygous for three Robertsonian translocations: an electron-microscopic study

A synaptonemal complex (SC) analysis was carried out in male mice heterozygous (CHT/+) for three Robertsonian translocations. All pachytene preparations studied showed the presence of three trivalents. At early pachytene, the nonhomologous centromeric regions of the acrocentric chromosomes were unpaired. Heterosynapsis subsequently took place with complete pairing of the trivalents. Association between one of the three trivalents and the sex vesicle was observed in 30.4% of the nuclei. Association between the unpaired regions of two trivalents was present in 14.4% of the cells, suggesting that the relationship between unpaired regions of structural rearrangements and the X-Y bivalent may simply reflect the tendency of unpaired regions to establish end-to-end associations or heterosynapses among them, which are usually resolved during the pachytene stage of prophase I. Since the sex bivalent always has unpaired regions, these associations often affect the sex chromosomes.     

The human endonexin II (ENX2) gene is located at 4q28----q32

A relatively recently identified family of structurally similar Ca2(+)-dependent phospholipid binding proteins is called the annexin gene family. At least seven genes are known, although their exact functions are unclear. The endonexin II gene (ENX2), one member of the gene family, is assigned to 4q28----q32 using both Southern transfer analysis of human x rodent somatic cell hybrid DNAs and in situ chromosome hybridization. One of the lipocortin II genes, another annexin, had previously been assigned to the long arm of chromosome 4.     

Enkephalin regulation of L-valine transport in rabbit ileum

We studied the influence on ionic basal transport (Na+ and Cl-) and L-valine transport of two enkephalins which are not metabolized and act in delta and mu receptors respectively. Transports have been indirectly determined measuring the transepithelial electric potential and the short circuit current. DADLE does not significantly influence ion and amino-acid transport, while DAGO alters both of them in the presence of the myenteric plexus (muscle layers present) or inhibits only L-valine transport in the absence of the plexus (muscle layers removed).     

The control of root, vegetative shoot and flower morphogenesis in tobacco thin cell-layer explants (TCLs)

Thin cell-layer explants (TCLs) have been proposed as favorable tissues for the study of root, vegetative shoot and flower formation. We tested the effects of pH, light quality, light quantity, and IBA and kinetin concentrations on the morphogenesis of TCLs cultured individually on a liquid medium. Alterations of the amounts of exogenously supplied IBA and kinetin were sufficient to induce the formation of roots, vegetative shoots and flowers on TCLs cultured on otherwise identical media. The type and number of organs formed were sensitive to the intensity of light (55, 75, 100 and 120 muEinsteins m-2 sec-1) under which TCLs were grown. Evidence was obtained that the effects of light on TCL morphogenesis were associated with photochemical degradation of IBA in the medium. Evaluation of the organogenesis that occurred in TCLs cultured on a medium containing a range of IBA and kinetin concentrations showed that the number and type of organs formed, and overall growth, were dependent upon the initial concentrations of auxin and cytokinin. We have developed the TCL culture system into a sensitive and reproducible bioassay for the study of morphogenesis. The advantages of using the TCL morphogenesis bioassay for the identification and study of molecules (e.g. cell wall oligosaccharides) that may regulate morphogenesis are discussed.