Solid-Phase Synthesis of Biaryl Cyclic Peptides Containing a Histidine-Phenylalanine Linkage

The feasibility of the solid-phase intramolecular 4(5)-arylation of a histidine residue to obtain biaryl cyclic peptides bearing a His-Phe linkage was esta     

Contribution to catalysis and stability of the five cysteines in Escherichia coli aspartate aminotransferase. Preparation and properties of a cysteine-free enzyme.

The five cysteines, at positions 82, 191, 192, 270, and 401, of Escherichia coli aspartate aminotransferase (AATase) were, individually and in some combinations, converted to alanine by site-directed mutagenesis (C82A, C191A, C192A, C270A, C401A). Cys-191, which is conserved in all AATase isozymes, was mutated to serine as well (C191S). A quintuple mutant, with all cysteines converted to alanines (Quint), was also constructed. The effects of these single and multiple mutations were examined by steady-state kinetics and urea denaturation. The thermal stabilities of Quint and of the wild-type enzyme (WT) were determined by differential scanning calorimetry. The mutants had kcat values up to 50% greater than that of WT and KMAsp and KM alpha-KG values up to 1.5- and 3.3-fold higher than that of WT. The mutants C82A and C191A exhibit nearly the same CM in urea denaturation experiments as WT, while the other single mutants and Quint are less stable, with CM differences of up to 0.7 M urea. Quint is also less thermostable than WT, with a delta TM of 3.3-4.4 degrees C. Thus the five cysteine replacements yield small, but significant, changes in catalytic and denaturation parameters, but none of the cysteines was found to be essential. The changes manifested in the mutation of the conserved Cys-191 to alanine are no greater than those observed with the four nonconserved cysteines. We consider the evolutionary implications of these findings.     

Iron metabolism in iron-deficient male quail

1. Male quails submitted 20 and 120 days to a low iron diet (7 ppm) were compared to female laying quails, exposed for 30 days to the same low iron regime, in order to compare the response of the iron metabolic control under a single (erythropoiesis) or a doubled (erythropoiesis and egg formation) iron demand. 2. Iron deposit in storage organs, the classical hematology and the intestinal iron absorption were analyzed in these animals. 3. In males, after 120 days, the iron deposits were reduced 50 and 75%, but hematological values (hematocrit and hemoglobin concentration) were normal, although in laying quails, after 30 days, an anemic condition was evident in both blood parameters and iron deposits, provoking an iron deficient erythropoiesis. 4. The enhancement of the intestinal iron uptake, confirms the anemic character of these birds.     

Cytogenetic study of F1 hybrids betweenCrepis dinarica andCrepis froelichiana (Asteraceae)

Crepis dinarica andC. froelichiana are two closely related species of theC. praemorsa complex. Even though they exhibit the same chromosome number (2n = 8) and similar idiogram shape, they differ widely in quantity and distribution of heterochromatin bands. The hybrids between these two species comprise three morphological types. Parental genomes were distinguished in hybrids by Giemsa differential staining (C-banding). Although meiosis presents only a few abnormalities (about 2.4%), the percentage of aborted pollen grains is very high (90%).     

Hemagglutination Inhibition with Arboviruses: Relationship Between Titers and Source of Erythrocytes

Antigens for Grand Arbaud, Hazara, and California arboviruses were able to agglutinate goose and either dog, hamster and guinea pig, or hamster red blood cells (RBC) to the same titer at the same pH; in hemagglutination-inhibition (HI) tests, titers for homologous and related sera were the same with these different types of RBC or occasionally one dilution higher with the mammalian cells. Antigens for St. Louis encephalitis and Eastern equine encephalitis viruses required use of lower antigen dilutions with human, guinea pig, and hamster RBC than with goose RBC. The results of comparative HI testing with these latter antigens and types of RBC indicate that HI titer is not directly related to the antigen dilution used with different types of RBC.     

Functional Expression of P-Glycoprotein in an Immortalised Cell Line of Rat Brain Endothelial Cells, RBE4

Abstract: The presence of P-glycoprotein in the cell plasma membrane limits the penetration of many cytotoxic substances into cells that express the gene product. There is considerable evidence also to indicate that P-glycoprotein is expressed as part of the normal blood-brain barrier in the luminal membranes of the cerebral capillary endothelial cells, where it presumably performs a protective function for the brain. This report describes the functional expression of P-glycoprotein in an immortalised cell line, RBE4, derived from rat cerebral capillary endothelial cells. The expression of P-glycoprotein is demonstrated by western immunoblotting and by immunogold and fluorescent staining with monoclonal antibodies. The cellular accumulation of [³H]colchicine and [³H]vinblastine is investigated and shown to be enhanced by the presence of azidothymidine, chlorpromazine, verapamil, cyclosporin A, and PSC 833 ([3'-keto-Bmt¹]-[Val²]-cyclosporin) at 50 or 100 µ M concentration. It is concluded that the RBE4 cell line is a valuable tool for investigating the mechanisms of P-glycoprotein activity both in the blood-brain barrier and in multidrug resistance in general.     

Enhanced production of lactic acid through the use of a novel aqueous two-phase system as an extractive fermentation system

 In order to enhance the productivity of lactic acid and reduce the end-product inhibition of fermentation, the partitioning and growth of four different strains of lactic acid bacteria in three different aqueous two-phase systems were studied. Polyethyleneglycol/ dextran, polyethyleneglycol/hydroxypropyl starch polymer (HPS), and a random copolymer of ethylene oxide and propylene oxide (EO-PO)/HPS were used as polymer systems. One strain each of Lactococcus lactis subsp. lactis and of Lactobacillus delbrueckii subsp. delbrueckii partitioned completely to the interface and bottom phase in two-phase systems with low polymer concentrations of EO-PO/HPS100 and EO-PO/ HPS200. The growth and production of lactic acid by two of three L. lactis strains in a two-phase system with 5.5% (w/w) EO-PO and 12.0% (w/w) HPS100 were reduced by less than 10% compared with a reference fermentation in a normal growth medium. The viability of L. lactis subsp. lactis ATCC 19435 was maintained for at least 50 h and with four top-phase replacements during extractive fermentation in the EO-PO/HPS100 system. Moreover, when cell density reached the stationary phase in the first extractive fermentation, the lactate production in this aqueous two-phase system was maintained. Received: 2 October 1995/Received revision: 16 January 1996/Accepted: 22 January 1996