Alternate mechanism for amino acid entry into Neurospora crassa: extracellular deamination and subsequent keto acid transport

The growth of the pm nbg mutant strain of Neurospora crassa was inhibited by the amino acid analog para-fluorophenylalanine despite the fact that none of the three constitutive amino acid permeases is functional in this strain. This observation led to the detection of both a deaminase which was released into the growth medium in response to para-fluorophenylalanine and a keto acid transport system which allowed entry of the resulting keto acid into the cell. The transported keto acid was recovered in cellular protein, suggesting its regeneration as the amino acid. The cooperative activity of these two systems represents an additional mechanism for the intracellular accumulation of amino acids, which is distinct from the known amino acid permeases.     

A specific binding protein for 1 alpha,25-dihydroxyvitamin D in the chick embryo chorioallantoic membrane

A 3.7 S binding protein for the steroid hormone and vitamin D metabolite 1 alpha-25-dihydroxyvitamin D (1,25-(OH)2-D) was observed in high salt cytosol extracts of chick embryo chorioallantoic membrane. The binding protein was characterized after partial purification of cytosol extracts by ammonium sulfate fractionation. The binding of 1,25-(OH)2-D was saturable, had a high affinity (Kd = 0.16 nM), and was specific for hormonally active vitamin D metabolites. Analysis of the displacement of [3H]1,25-(OH)2-D by unlabeled analogues showed the affinities of vitamin D metabolites to be in the order of 1,25-(OH)2-D = 1,24R,25-(OH)3-D much greater than 25-OH-D = 1-OH-D greater than 24R,25-(OH)2-D. Hormone binding was sensitive to pretreatment with sulfhydryl-blocking reagents. The chorioallantoic membrane 1,25-(OH)2-D-binding protein associated with the chromatin fraction after homogenization of membranes in low salt buffer, and bound to DNA-cellulose columns, eluting as a single peak at 0.215 M KCl. These findings support identification of this 1,25-(OH)2-D-binding protein as a steroid hormone receptor, with properties indistinguishable from 1,25-(OH)2-D receptors in other chick tissues. The chorioallantoic membrane functions in the last third of embryonic development to reabsorb calcium from the eff shell for deposition in embryonic bone. 1,25-(OH)2-D binding activity in the chorioallantoic membrane increased 4- to 5-fold from day 12 to day 16 of incubation, immediately preceding the onset of shell reabsorption. This finding suggests that 1,25-(OH)2-D may act to regulate shell mobilization and transepithelial calcium transport by the chorioallantoic membrane. Finally, the similarity of shell mobilization to bone resorption, which is also stimulated by 1,25-(OH)2-D, suggests that the chorioallantoic membrane is a useful alternate model for the study of 1,25-(OH)2-D action on bone mineral metabolism.     

Sur une flore a Glossopteropsida et Lycopsida de Namibie (Sud-Ouest Africain)

The study of imprints of fossil plants collected in the Permian from the country of Hammanskraal (Namibia) leads to the following identifications: Glossopteris sp., Gangamopteris sp., Noegerrathiopsis sp., Gondwanidium sp., Asterotheca sp. and Lycopodiopsis derbyiB. Renault, Lycopodiopsis costilatus n. sp., Brasilodendron pedroanum(W. Carruthers) W.G. Chaloner & alii, Brasilodendron africanum n. sp. This flora has affinities with some fossil floras from South Africa and from Brazil, and is, probably, of upper Permian age.     

Revision du genre LycopodiopsisB. Renault, 1890

The study of imprints of Lycopsida from Permianof the Gondwana has permitted to specify the organisation of the leaf cushions and their variation in the genus LycopodiopsisB. Renault. The presence of a ligula is showed off. The invalidity of the genera Cyclodendron and Lycopodiophloios is demonstrated, and the species refered to these genera must be refered to the genus Lycopodiopsis for which an emended diagnosis is proposed.     

The estradiol-stimulated lipoprotein receptor of rat liver. A binding site that membrane mediates the uptake of rat lipoproteins containing apoproteins B and E

Hepatic catabolism of lipoproteins containing apolipoproteins B or E is enhanced in rats treated with pharmacologic doses of 17 alpha-ethinyl estradiol. Liver membranes prepared from these rats exhibit an increased number of receptor sites that bind 125I-labeled human low density lipoproteins (LDL) in vitro. In the present studies, this estradiol-stimulated hepatic receptor was shown to recognize the following rat lipoproteins: LDL, very low density lipoproteins obtained from liver perfusates (hepatic VLDL), and VLDL-remnants prepared by intravenous injection of hepatic VLDL into functionally eviscerated rats. The receptor also recognized synthetic lamellar complexes of lecithin and rat apoprotein E as well as canine high density lipoproteins containing apoprotein E (apo E-HDLc). It did not recognize human HDL or rat HDL deficient in apoprotein E. Much smaller amounts of this high affinity binding site were also found on liver membranes from untreated rats, the number of such sites increasing more than 10-fold after the animals were treated with estradiol. Each of the rat lipoproteins recognized by this receptor was taken up more rapidly by perfused livers from estrogen-treated rats. In addition, enrichment of hepatic VLDL with C-apoproteins lowered the ability of these lipoproteins to bind to the estradiol-stimulated receptor and diminished their rate of uptake by the perfused liver of estrogen-treated rats, just as it did in normal rats. The current data indicate that under the influence of pharmacologic doses of estradiol the liver of the rat contains increased amounts of a functional lipoprotein receptor that binds lipoproteins containing apoproteins B and E. This hepatic lipoprotein receptor appears to mediate the uptake and degradation of lipoproteins by the normal liver as well as the liver of estradiol-treated rats. The hepatic receptor bears a close functional resemblance to the LDL receptor previously characterized on extrahepatic cells.     

Assignment to chromosome 16 of a gene necessary for the expression of human mitochondrial glutamate oxaloacetate transaminase (aspartate aminotransferase) (E.C. 2.6.1.1.)

A gene necessary for the expression of human mitochondrial glutamate oxaloacetate transaminase (GOT-2) has been assigned to chromosome 16 on the basis of an immunochemical analysis of human-mouse somatic cell hybrids. Mitochondrial GOT cosegregates with adenine phosphoribosyl transferase (E.C. 2.4.2.7.).     

Radioimmunoassay for the detection and quantitation of bruceantin

A radioimmunoassay for a new anticancer drug, bruceantin, has been developed using [³H]acetylbruceantin and antibody induced by immunizing rabbits with succinylbruceantin-bovine serum albumin conjugates. [³H]Acetylbruceantin was synthesized by reacting bruceantin with [³H]acetyl anhydride. The assay is simple and reproducible. The standard curve was linear on a logit-log plot, and the lower limit of sensitivity of the assay was 1 ng/ml. Using this assay, drug levels were easily determined in tissues of experimental animals following bruceantin administration. The assay procedure does not require sample extraction for plasma, urine, and bile. Bruceantin in other tissues can be extracted quantitatively with ethanol before being measured by the radioimmunoassay.     

Detergent induced inhibition of eukaryotic RNA polymerase B activity and amanitin binding

We studied the effect of detergents on the binding of amanitin to RNA polymerase and on enzymatic activity. SDoS, Sarkosyl and deoxycholate were most inhibitory. Cholate and non-ionic detergents were less inhibitory. Evidence is presented that Sarkosyl inhibits chain elongation. The inhibition of amanitin binding was most influenced by the hydrophilicity of the detergent.