Estrogen-Induced Synthesis of Yolk Proteins in Roosters

Vitellogenin is the serum precursor of the yolk proteins -lipovitellin,rß-lipovitellin, and phosvitin. The precursor canbe dissociated to produce the yolk proteins only by proteolyticenzymatic action, to which it is very susceptible. Denaturationin sodium dodecyl sulfate, combined with reduction of disulfidebridges and blocking of thiols, yields a complex with a molecularweight of 200,000 to 250,000. -Lipovitellin contains three polypeptides,with molecular weights of about 135,000, 105,000, and 40,000,and rß-lipovitellin is composed of two polypeptidechains with molecular weights of 135,000 and 30,000. The 40,000subunit of -lipovitellin and both rß-lipovitellinsubunits are phosphopeptides We tested RNA isolated from the liver of estrogen-treated roostersfor mRNA activity in a cell-free reticulocyte system. The vitellogeninmRNA has a sedimentation coefficient greater than 28S and thuscontains enough information to code for a long polypeptide chain.Estrogen administration to roosters induces the appearance ofvitellogenin and a lowdensity lipoprotein, the syntheses ofwhich are not coordinated. The course of vitellogenin synthesiswas calculated from accumulation and turnover data, and it wasfound that from about 25 hr after estradiol-17rß administrationthe rate of vitellogenin synthesis increases linearly for severaldays, paralleling an increase in vitellogenin-synthesizing polysomes.Thus, we estimate a constant translation rate of about 8 aminoacids per ribosome per sec. A "memory" effect is observed when a second hormone dose isgiven some time after the vitellogenin induced by the firstdose has disappeared from the blood. After the second dose vitellogeninsynthesis is detected sooner, and its initial increase is morerapid, than after the first dose. Although the synthesis ofvitellogenin starts 3 to 4 hr after the second as well as afterthe first injection, the rate of synthesis after the first injectionincreases much more slowly during the first 15 hr than duringthe subsequent period of linear accumulation, whereas afterthe second injection the linear increase in the rate of synthesisbegins immediately after the lag period of 3 to 4 hr. The "memory"effect is undiminished even 50 days after the first hormonedose; thus, the causative factor either is very stable or issynthesized in great excess during the first stimulation. Whenthe second injection is given during the descending part ofthe turnover curve, an increase in vitellogenin synthesis isobserved within 3.5 hr. There are thus at least three different effects of estradiol;(i) the "memory" effect, which probably is due to commitmentor differentiation of vitellogenin-synthesizing cells; (ii)the effect that causes the committed cells to give full responseafter the 3- to 4-hr lag period; and (iii) the effect that causesthe immediate response. To explain these results we suggestthat committed cells can synthesize vitellogenin mRNA only duringa certain period of the cell cycle.     

Different incorporation of glucocorticoid hormone into diploid and tetraploid liver nuclei

Tetraploid parenchymal rat liver nuclei incorporate about twice as much (³H)dexamethasone as diploid parenchymal nuclei both in vivo and in vitro. This suggests that the ability of hepatic nuclei to incorporate glucocorticoid hormone is influenced by the number of copies of the genome in these nuclei.     

Destabilization of the Homotetrameric Assembly of 3-Deoxy-d-Arabino-Heptulosonate-7-Phosphate Synthase from the Hyperthermophile Pyrococcus furiosus Enhances Enzymatic Activity

Many proteins adopt homomeric quaternary structures to support their biological function, including the first enzyme of the shikimate pathway that is ultimately responsible for the biosynthesis of the aromatic amino acids in plants and microorganisms. This enzyme, 3-deoxy-d-arabino-heptulosonate-7-phosphate synthase (DAH7PS), adopts a variety of different quaternary structures depending on the organism in which it is found. The DAH7PS from the hyperthermophilic archaebacterium Pyrococcus furiosus was previously shown to be tetrameric in its crystalline form, and this quaternary association is confirmed in an improved structure in a different crystal system. This tetramer is also present in solution as revealed by small-angle X-ray scattering and analytical ultracentrifugation. This homotetrameric form has two distinct interfaces, both of which bury over 10% each of the surface area of a single monomer. Substitution of Ile for Asp in the hydrophobic region of one interface gives a protein with a remarkable 4-fold higher maximum catalytic rate than the wild-type enzyme. Analytical ultracentrifugation at pH 7.5 reveals that the tetrameric form is destabilized; although the protein crystallizes as a tetramer, equilibrium exists between tetrameric and dimeric forms with a dissociation constant of 22 μM. Thus, under the conditions of kinetic assay, the enzyme is primarily dimeric, revealing that the dimeric form is a fully functional catalyst. However, in comparison to the wild-type protein, the thermal stability of the dimeric protein is significantly compromised. Thus, an unusual compromise of enzymatic activity versus stability is observed for this DAH7PS from an organism that favors a hyperthermophilic environment.     

Absorption,tissue distribution,metabolism and elimination of taurine given orally to rats

Summary. Three biodisposition studies with taurine were performed in male and female adult rats at dosages of 30 and 300 mg/kg. A single oral dose of ¹⁴C-taurine was rapidly absorbed, distributed to tissues and excreted unchanged in urine. Elimination of radioactivity from intracellular pools was slow. Pre-treatment of animals for 14 days with unlabelled taurine did not significantly affect the fate of ¹⁴C-taurine. At the higher dose there was more extensive excretion combined with a lower percentage of the dose in the carcass, indicating the possibility of saturation of the tubular reabsorption mechanism for taurine. Daily administration of unlabelled taurine for 14 days did not result in an increase in total taurine in the brain. The data indicate that exogenous taurine rapidly equilibrates with endogenous body pools and that any excess is rapidly eliminated by the kidneys.     

Nucleotide sequence of a chicken vitellogenin gene and derived amino acid sequence of the encoded yolk precursor protein

The gene encoding the major vitellogenin from chicken has been completely sequenced and its exon-intron organization has been established. The gene is 20,342 base-pairs long and contains 35 exons with a combined length of 5787 base-pairs. They encode the 1850-amino acid pre-peptide of vitellogenin, which is the precursor of the mature yolk proteins, the serine-rich and heavily phosphorylated phosvitin and the lipovitellin. The 217-amino acid phosvitin polypeptide occupies an internal position (residue 1112 through 1328) within the vitellogenin molecule. The 125,000 and 30,000 Mr lipovitellin polypeptides are encoded by the sequences at the N-terminal and the C-terminal sides of the phosvitin section, respectively. The main features of the gene and protein sequences, and the evolutionary implications, are discussed.     

Isolation of beauvericin as an insect toxin from Fusarium semitectum and Fusarium moniliforme var. subglutinans

Nonpolar methylene chloride-soluble extracts from the mycelia of Fusarium semitectum and Fusarium moniliforme var. subglutinans were toxic to Colorado potato beetles. The major toxic metabolite was isolated and found to be the cyclodepsipeptide, beauvericin. This is the first report of the isolation of beauvericin from the genus Fusarium.     

Oxidation products of terpenes identified from Dendroctonus and Ips bark beetles

Exposure of adult males and females of Dendroctonus brevicomis and D. frontalis to camphene vapor resulted in oxidation of the terpene to a prominent product, which was identified as 6-hydroxy-camphene (camphenol). Exposure of D. brevicomis adults to myrcene vapor resulted in sex-specific oxidation of the hydrocarbon. A major product in both sexes was identified as 2-methyl-6-methylene-2,7-octadien-1-ol (myrcenol), whereas ipsdienol, a major product in males, was not detected in females. A compound detected in hindguts of feeding males of Ips pini and I. paraconfusus was attributed to the presence of 3-carene in the host (Pinus spp.) and subsequently identified as 1-methyl-5-(α-hydroxy-isopropyl)-cyclohexa-1,3-diene.     

Cover Image,Volume 88, Issue 5

Human pathogenic and commensal bacteria have evolved the ability to scavenge host-derived sialic acids and subsequently degrade them as a source of nutrition. Expression of the Escherichia coli yjhBC operon is controlled by the repressor protein nanR, which regulates the core machinery responsible for the import and catabolic processing of sialic acid. The role of the yjhBC encoded proteins is not known—here, we demonstrate that the enzyme YjhC is an oxidoreductase/dehydrogenase involved in bacterial sialic acid degradation. First, we demonstrate in vivo using knockout experiments that YjhC is broadly involved in carbohydrate metabolism, including that of N-acetyl-d -glucosamine, N-acetyl-d -galactosamine and N-acetylneuraminic acid. Differential scanning fluorimetry demonstrates that YjhC binds N-acetylneuraminic acid and its lactone variant, along with NAD(H), which is consistent with its role as an oxidoreductase. Next, we solved the crystal structure of YjhC in complex with the NAD(H) cofactor to 1.35 Å resolution. The protein fold belongs to the Gfo/Idh/MocA protein family. The dimeric assembly observed in the crystal form is confirmed through solution studies. Ensemble refinement reveals a flexible loop region that may play a key role during catalysis, providing essential contacts to stabilize the substrate—a unique feature to YjhC among closely related structures. Guided by the structure, in silico docking experiments support the binding of sialic acid and several common derivatives in the binding pocket, which has an overall positive charge distribution. Taken together, our results verify the role of YjhC as a bona fide oxidoreductase/dehydrogenase and provide the first evidence to support its involvement in sialic acid metabolism.