Plant Cell Wall Carbohydrates as Substrates for Azospirillum brasiliense

Carbohydrate components (simple sugars and polysaccharides) of cell walls of pearl millet (Pennisetum americanum L., cv. Gahi) were studied as potential substrates for the root-associated diazotroph Azospirillum brasiliense Sp. 7. Simple sugars were utilized, but no evidence was obtained to support the suggestion that the polysaccharide components tested might serve as substrates for growth following hydrolysis by the associated azospirilla.     

Rational construction of a 2-hydroxyacid dehydrogenase with new substrate specificity

Using site-directed mutagenesis on the lactate dehydrogenase gene from Bacillus stearothermophilus, three amino acid substitutions have been made at sites in the enzyme which we suggest in part determine specificity toward different hydroxyacids (R-CHOH-COOH). To change the preferred substrates from the pyruvate/lactate pair (R = -CH3) to the oxaloacetate/malate pair (R = -CH2-COO-), the volume of the active site was increased (thr 246----gly), an acid was neutralized (asp-197----asn) and a base was introduced (gln-102 - greater than arg). The wild type enzyme has a catalytic specificity for pyruvate over oxaloacetate of 1000 whereas the triple mutant has a specificity for oxaloacetate over pyruvate of 500. Despite the severity and extent of these active site alterations, the malate dehydrogenase so produced retains a reasonably fast catalytic rate constant (20 s-1 for oxaloacetate reduction) and is still allosterically controlled by fructose-1,6-bisphosphate.     

Factor XIII binds to the A alpha- and B beta- chains in the D-domain of fibrinogen: an immunoblotting study

The binding sites in fibrinogen for Factor XIII were localized using an immunoblotting technique. Platelet Factor XIII bound to fibrinogen and to plasmin degradation products of fibrin(ogen) including Fragments: X, D1-D3, and D-dimer, but did not bind to Fragment E. Binding of Platelet Factor XIII was independent of calcium ions but could be inhibited by the presence of 0.5 M NaCl. Binding could also be inhibited by preincubating Factor XIII with a 100-fold molar excess of fibrinogen but not by 100-fold molar excess of Fragment E. Binding of Factor XIII to fibrinogen was specific, since several other proteins tested (ovalbumin, bovine serum albumin, alpha 2-macroglobulin, beta-galactosidase, fructose kinase, lactic dehydrogenase, triose phosphate isomerase, fumarase and pyruvate kinase) did not bind Factor XIII. Furthermore, binding was not observed either when Factor XIII was left out or when antiFactor XIII antiserum was substituted with nonimmune serum. When fibrinogen was reduced prior to electrophoresis, Factor XIII bound to the A alpha and B beta chains of fibrinogen and des A,B fibrinogen, the B beta-chain of Fragment X, but not the gamma-chains. Localization of the Factor XIII binding sites to the carboxy terminal segments of the A alpha and B beta chains in the Fragment D-domain of fibrinogen could have important physiological consequences.     

Age-related changes in testicular development and reproductive endocrinology associated with aflatoxicosis in the male chicken

A study was conducted to investigate endocrine and testicular changes in the male chicken associated with the ingestion of 10 or 20 ppm aflatoxin at 3 different stages of development. Weekly body weight gain, absolute and relative combined testes weights, and plasma testosterone concentrations were reduced in aflatoxin-fed males as compared to controls, with the greatest differences seen at 12 wk of age. The effect of dietary aflatoxin on levels of plasma luteinizing hormone (LH) was dependent on age at exposure. Concentrations of plasma LH in 6-wk-old control males were significantly higher than in aflatoxin-fed birds, whereas no treatment differences were observed in older males. Additionally, few changes were observed in static levels of monoamines in any of the brain regions assayed, regardless of age at exposure. The delay in peak levels of LH, as well as the suppression of plasma testosterone and testicular weight, indicate a possible delay in the onset of sexual maturation associated with aflatoxicosis in this species.     

Steroid feedback inhibition of pulsatile secretion of gonadotropin-releasing hormone in the ewe

The long-term negative feedback effects of sustained elevations in circulating estradiol and progesterone on the pulsatile secretion of gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) were evaluated in the ewe following ovariectomy during the mid-late anestrous and early breeding seasons. GnRH secretion was monitored in serial samples of hypophyseal portal blood. Steroids were administered from the time of ovariectomy by s.c. Silastic implants, which maintained plasma concentrations of estradiol and progesterone at levels resembling those that circulate during the mid-luteal phase of the estrous cycle; control ewes did not receive steroidal replacement. Analysis of hormonal pulse patterns in serial samples during 6-h periods on Days 8-10 after ovariectomy disclosed discrete, concurrent pulses of GnRH in hypothalamo-hypophyseal portal blood and LH in peripheral blood of untreated ovariectomized ewes. These pulses occurred every 97 min on the average. Treatment with either estradiol or progesterone greatly diminished or abolished detectable pulsatile secretion of GnRH and LH, infrequent pulses being evident in only 3 of 19 steroid-treated ewes. No major seasonal difference was observed in GnRH or LH pulse patterns in any group of ewes. Our findings in the ovariectomized ewe provide direct support for the conclusion that the negative-feedback effects of estradiol and progesterone on gonadotropin secretion in the ewe include an action on the brain and a consequent inhibition of pulsatile GnRH secretion.     

Pituitary receptors for gonadotropin-releasing hormone in relation to changes in pituitary and plasma luteinizing hormone in ovariectomized-hypothalamo pituitary disconnected ewes. I. Effect of changing frequency of gonadotropin-releasing hormone pulses

Studies were undertaken to determine if changes in the amplitude of luteinizing hormone (LH) pulses that occur in response to changes in the frequency of gonadotropin-releasing hormone (GnRH) pulses are due to an alteration in the number of GnRH receptors. Ewes were ovariectomized (OVX) and the hypothalamus was disconnected from the pituitary (HPD). Ewes were then given pulses of GnRH at a frequency of 1/h or 1/3 h. Two control groups were included: OVX ewes not subjected to HPD, and HPD ewes that were not OVX. At the end of one week of treatment, blood samples were collected to determine the amplitude of LH pulses. The treated ewes were killed just before the next scheduled pulse of GnRH, and the content of LH and number of GnRH receptors were measured in each pituitary. The amplitude of LH pulses was highly correlated with the amount of LH in the pituitary gland (r = 0.71, p less than 0.01), and both LH content and pulse amplitude (mean + SEM) were higher in ewes receiving GnRH once per 3 h (189.7 +/- 39.3 microgram/pituitary, 10.3 +/- 1.1 ng/ml, respectively) than in ewes receiving GnRH once per h (77.8 +/- 11.4 microgram/pituitary, 5.2 +/- 1.3 ng/ml). The pituitary content of LH was highest in the OVX ewes (260.2 +/- 57.4 micrograms/pituitary) and lowest in the nonpulsed HPD ewes (61.7 +/- 51.2 micrograms/pituitary). The number of GnRH receptors was similar in all groups, and was not correlated with any other variable.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of propoxur exposure on females of the German cockroach, Blattela germanica and their oothecae

Susceptible and insecticide resistant females of Blattella germanica (L.), Dictyoptera, were exposed to propoxur treated surfaces. They carried oothecae that were expected to hatch in 48 to 72 h. Hatch was delayed in females that retained their oothecae throughout the exposure period. Oothecal hatch and nymphal survival were reduced when oothecae hatched on a treated surface but not when oothecae were retained and hatched on an insecticide-free surface. Over half of the susceptible strain females dropped their oothecae during the exposure period while very few resistance females dropped oothecae prematurely. Mortality of susceptible females that dropped their oothecae was higher than among those that retained oothacea. A tendency in this direction was apparent among the few resistant females that dropped their oothecae. The number of nymphs that emerged on the treated surface and also that survived for 24 h was higher in the resistant than in the susceptible strain. Newly hatched nymphs were frequently attached to the oothecae due to an inability to shed the embryonic cuticle.

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Résumé Des femelles de B. germanica, sensibles ou résistantes aux insecticides, ont été mises en présence de surfaces traitées au propoxure. Elles portaient des oothèques dont l'éclosion était attendue entre 48 et 72 h plus tard. Les éclosions ont été retardées, les femelles ayant conservé leurs oothèques pendant toute la période d'exposition. Lex taux d'éclosion des oothèques et de survie larvaire ont été normaux quand il y a eu rétention de l'oothèque et émission sur une surface saine, par contre ils étaient réduits quand l'oothèque a été émise sur une surface traitée. Plus de la moitié des femelles de la souche sensible ont laché leur oothèque pendant la période d'exposition tandis que très peu de femelles de la souche résistante ont abandonné leur oothèque prématurément. La mortalité était plus élevée chez les femelles sensibles qui ont perdu leur oothèque que chez celles qui l'avaient conservée. Une tendance du même type était décelable parmi les quelques femelles de la souche résistante qui perdirent leur oothèque. Le nombre d'écolosions de larves et le nombre de survies larvaires à 24 h étaient plus élevés dans la souche résistante que dans la souche sensible. Les larves néonates étaient souvent fixées à l'oothèque par suite de leur incapacité à se dépouiller de la cuticle embryonnaire.

     

A reply to Holmes on Gendercide

Warren's book, Gendercide: The Implications of Sex Selection (Totowa, N.J.: Rowman and Allanheld; 1985), was reviewed by Helen Bequaert Holmes in the January 1987 issue of Bioethics. Here, Warren responds to the review by clarifying some of her moral arguments and continuing to defend the point of view that selecting the sex of children before conception or before birth is not always sexist, socially harmful, or disrespectful of the child as an end in itself.     

Isolation and1H-NMR spectroscopic identification of the glucose-containing lipid-linked precursor oligosaccharide ofN-linked carbohydrate chains

The lipid-linked precursor ofN-type glycoprotein oligosaccharides was isolated from porcine thyroid microsomes after in cubation with UDP[³H] Glucose. The carbohydrate was released from dolichol pyrophosphate by mild acid hydrolysis, purified by gel filtration and characterized by 500-MHz¹H-NMR spectroscopy in combination with enzymatic degradation. The parent oligosaccharide was found to be Glc₃Man₉Glc-NAc₂. The three glucose residues are present in the linear sequence Glcα1-2Glα1-3 Glc, the latter being α(1-3)-linked to one of the mannose residues. In order to establish the branch location of the triglucosyl unit, the parent compound was digested with jack-bean α-mannosidase. The oligosaccharide product was purified by gel filtration, and identified by¹H-NMR as Glc₃Man₅GlcNAc₂ lacking the mannose residues A, D₂, B and D₃. Therefore, the structure of the precursor oligosaccharide is as follows: $$\begin{gathered} c b a D_1 C 4 \hfill \\ Glc\alpha 1 - 2Glc\alpha 1 - 3Glc\alpha 1 - 3Man\alpha 1 - 2Man\alpha 1 - 2Man\alpha 1 \hfill \\ 3 \swarrow 3 2 1 \hfill \\ Man\alpha 1 - 2Man\alpha 1 Man\beta 1 - 4GlcNAc\beta 1 - 4GlcNAc \hfill \\ D_{2 } A 3 6 \hfill \\ Man\alpha 1 \hfill \\ 6 \hfill \\ Man\alpha 1 - 2Man\alpha 1 \nwarrow 4 \hfill \\ D_3 B \hfill \\ \end{gathered} $$