Iron accumulation and neurotoxicity in cortical cultures treated with holotransferrin

Nonheme iron accumulates in CNS tissue after ischemic and hemorrhagic insults and may contribute to cell loss. The source of this iron has not been precisely defined. After blood-brain barrier disruption, CNS cells may be exposed to plasma concentrations of transferrin-bound iron (TBI), which exceed that in the CSF by over 50-fold. In this study, the hypothesis that these concentrations of TBI produce cell iron accumulation and neurotoxicity was tested in primary cortical cultures. Treatment with 0.5-3 mg/ml holotransferrin for 24 h resulted in the loss of 20-40% of neurons, associated with increases in malondialdehyde, ferritin, heme oxygenase-1, and iron; transferrin receptor-1 expression was reduced by about 50%. Deferoxamine, 2,2′-bipyridyl, Trolox, and ascorbate prevented all injury, but apotransferrin was ineffective. Cell TBI accumulation was significantly reduced by deferoxamine, 2,2′-bipyridyl, and apotransferrin, but not by ascorbate or Trolox. After treatment with ⁵⁵Fe-transferrin, approximately 40% of cell iron was exported within 16 h. Net export was increased by deferoxamine and 2,2′-bipyridyl, but not by apotransferrin. These results suggest that downregulation of transferrin receptor-1 expression is insufficient to prevent iron-mediated death when neurons are exposed to plasma concentrations of TBI. Chelator therapy may be beneficial for acute CNS injuries associated with loss of blood-brain barrier integrity.     

Dynamic approaches to the mechanism of photosynthesis

An account of the author's life and scientific research is presented. Two main lines of research have been pursued: (1) Studies on the physiological aspect of photosynthesis started from experiments with crops under field conditions and then extended to the study of photosynthesis in nature; and (2) studies on the mechanism of photophosphorylation and related problems which began with the measurement of quantum requirement of photophosphorylation. This work led to the discovery of the mg src="/content/q2mg1227n6414m23/xxlarge8216.gif" alt="lsquo" align="BASELINE" BORDER="0">high energy statemg src="/content/q2mg1227n6414m23/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0"> of phosphorylation and many other interesting findings. In recent years, efforts have been made to study the operation and regulation of photosynthetic apparatus with a view to link the above-mentioned lines of research together.Written at the invitation of Govindjee.     

Investigating serum factors promoting erythrocytic growth of Plasmodium falciparum

The elucidation of factors inducing the growth of Plasmodium falciparum can provide critical information about the developmental mechanisms of this parasite and open the way to search for novel targets for malaria chemotherapy. The ability of components of a growth-promoting factor derived from bovine serum and various related substances to sustain growth of P. falciparum was characterized. A simple total lipid fraction (GFS-C) containing non-esterified fatty acids (NEFAs) as essential factors was noted to promote the parasite's growth. Various proteins from a variety of animals were tested, indicating the importance not only of GFS-C, but also of specific proteins, such as bovine and human albumin, in the parasite growth. Several combinations of the NEFAs tested sustained low parasite growth. Among various phospholipids and lysophospholipids tested, lysophosphatidylcholine containing C-18 unsaturated fatty acids was found to sustain the complete development of the parasite in the presence of bovine albumin. Several other lysophospholipids can partially support growth of P. falciparum.     

Chromatography of human urinary erythropoietin and granulocyte colony-stimulating factor on insolubilized phytohaemagglutinin

Human urinary erythropoietin was adsorbed to phytohaemagglutinin coupled to agarose or porous glass and quantitatively eluted by a saturated solution of MgCl₂. This method provides a means of separating erythropoietin from several of its contaminants, presumably on the basis of its carbohydrate side chains. Erythropoietin which had been purified by chromatography on insolubilized phytohaemagglutinin was sufficiently free of toxicity to be assayable in tissue culture even when crude urine was used as a starting material.     

Studies of Antarctic yeast for β-glucosidase production

Moss and lichen samples from the region of the Bulgarian base on Livingston Island, Antarctica were examined for the presence of yeasts. Six pure cultures were obtained. They were screened for mg src="/content/gy7x8q6mg08xchff/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-glucosidase production and two of them were selected. These were identified as Cryptococcus albidus AL₂ and C. albidus AL₃, according to their morphology, reproductive behaviour, and growth at different temperatures, salt concentrations, nutritional characteristics and various biochemical tests. These strains were examined for biosynthesis of mg src="/content/gy7x8q6mg08xchff/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-glucosidase on different carbon sources under aerobic conditions. High exocellular and endocellular activities were obtained when they were grown on cellobiose, methyl-mg src="/content/gy7x8q6mg08xchff/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-D-glucopyranoside and salicin. The time course of growth and mg src="/content/gy7x8q6mg08xchff/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-glucosidase production of the yeast was examined by cultivation in a medium with cellobiose under aerobic conditions at temperatures 18 and 24 °C for 96 h. Cryptococcus albidus AL₂ and C. albidus AL₃ synthesized exocellular enzyme, respectively 58.33 and 55.83 U/ml and endocellular enzyme 137.75 and 205.34 U/ml at 24 °C for 72 h of the cultivation.     

The signaling pathway in histidine kinase and the response regulator complex revealed by X-ray crystallography and solution scattering

The structure of a histidine kinase (ThkA) complexed with a response regulator (TrrA) in the two-component regulatory system from hyperthermophile Thermotoga maritima was determined by a combination of X-ray crystallography at a resolution of 4.2 A and small-angle X-ray scattering (SAXS). The boundary of the three component domains (PAS-sensor, dimerization and catalytic domains) of ThkA and the bound TrrA molecule were unambiguously assigned in the electron density map at 4.2 A resolution. ThkA forms a dimer with crystallographic 2-fold symmetry and two monomeric TrrAs bind to the ThkA dimer. SAXS experiments also confirmed this association state in solution and specific binding between ThkA and TrrA (Kd=8.2x10(-11) M(-2)). The association interface between ThkA and TrrA contains the phosphotransfer His residue in the ThkA, indicative of an efficient receipt of the phosphoryl group. One Per-Arnt-Sim (PAS) domain does not interact with the other PAS domain, but with the catalytic domain of the same polypeptide chain and with one TrrA molecule. Observed inter-domain and inter-molecular interactions reveal a definite pathway of signal transduction in the kinase/regulator complex. In addition, we propose a responsible role of TrrA for the feedback regulation of sensing and/or kinase activities of ThkA.     

Multiorgan autoimmunity in a Turner syndrome patient with partial monosomy 2q and trisomy 10p

Turner syndrome is a condition caused by numeric and structural abnormalities of the X chromosome, and is characterized by a series of clinical features, the most common being short stature and gonadal dysgenesis. An increased frequency of autoimmune diseases as well as an elevated incidence of autoantibodies has been observed in Turner patients.     

NADPH-dependent metabolism of 17beta-estradiol and estrone to polar and nonpolar metabolites by human tissues and cytochrome P450 isoforms

The endogenous estrogens, 17beta-estradiol (E(2)) and estrone (E(1)), undergo extensive metabolism in animals and humans, and a large number of their hydroxylated and keto metabolites have been identified in biological samples. The formation of most of the oxidative estrogen metabolites is catalyzed by cytochrome P450 (CYP) enzymes. Precise knowledge of the CYP-mediated formation of these metabolites, particularly those with unique biological activities (e.g., 4-hydroxy-E(2), 16alpha-hydroxy-E(1), 15alpha-hydroxy-E(2), 16-epiestriol, and 2-methoxyestradiol) in human liver and extrahepatic target tissues and cells, would add significantly to our understanding of the diverse biological functions that are associated with endogenous estrogens. In this article, we review recent results on the NADPH-dependent metabolism of endogenous estrogens to polar (hydroxylated and keto) metabolites as well as to nonpolar metabolites by human tissues and recombinant human CYP isoforms. The available data show that a large number of polar and nonpolar metabolites of E(2) and E(1) are formed by human tissues, and a variety of human CYP isoforms are involved in the NADPH-dependent formation of polar as well as nonpolar estrogen metabolites. These enzymes have varying degrees of catalytic activity and distinct regioselectivity.