Enzymic degradation of allantoate in developing soybeans

A Mn²⁺-dependent enzymic breakdown of allantoate has been detected in crude and partially purified extracts of developing soybeans. The products detected were CO₂, NH₃, glyoxylate, labile glyoxylate derivatives, and low levels of urea. Urea is initially produced at less than 10% the rate of urease-independent CO₂ release indicating that the activity is not allantoate amidinohydrolase (i.e. urea is not directly cleaved off allantoate). The urease-independent CO₂ releasing activity has an apparent K_m of 1.0 millimolar for allantoate. Ethylenediaminetetraacetate, borate, and acetohydroxamate (all at 10 millimolar) inhibit the enzymic production of NH₃, CO₂, and labile glyoxylate derivatives from allantoate. However, the potent urease inhibitor, phenyl phosphordiamidate does not inhibit CO₂ and NH₃ release indicating that the action of acetohydroxamate is not due to its inhibition of urease. That the allantoatedegrading activity was more than 5-fold greater in seed coats than in embryos is consistent with the data of Rainbird et al. (Plant Physiol 1984 74: 329-334) which indicate that available ureides are metabolized before reaching the embryo. 2-Ethanolthio, 2′ureido, acetic acid (NH₂COHNCHCO₂HSCH₂CH₂OH), the first allantoate-derived product detected by HPLC analysis, is an addition produced of mercaptoethanol with an unidentified enzymically produced ureido intermediate that is not derived from ureidoglycolate or oxalurate.     

Demonstration of neural induction using nuclear markers inXenopus

Summary Two nuclear markers were used to investigate the origin of cells in secondary embryos ofXenopus induced by dorsal lip transplants, and to determine the ability of the chordomesoderm to direct cells to change their fates.³H-thymidine was used to label cells transplanted between individualX. laevis embryos, and nuclear quinacrine fluorescence was used to distinguishX. borealis tissues transplanted toX. laevis hosts. In the first set of experiments, dorsal lip tissue (also known as the dorsal marginal zone; DMZ) was transplanted to the ventral marginal zone (VMZ) of host embryos. The marginal zone is the toroid of presumptive mesodermal cells which involutes during gastrulation. Examination of the secondary embryos resulting from these grafts revealed that their notochords were derived almost exclusively from transplanted cells whereas their nervous systems and somites were composed almost entirely of host cells. Next, the nuclear markers were used to show the normal fates of the tissue of the ventral equatorial region immediately above the VMZ by orthotopic grafting. This tissue was found to give rise to structures in the ventral posterior portions of the tailbud embryo. Finally, the same ventral tissue was labeled and transplanted to the dorsal equatorial region above the DMZ. As a result, it was induced to change its fate and become neural. These results lend unequivocal support to Spemann's theory of neural induction which has recently been questioned.     

A new species of the genus Spiroxys (Nematoda; Spiruroidea) from Australian chelonians of the genus Chelodina (Chelidae)

Summary Spiroxys chelodinae n. sp. is described from Australia in three species of freshwater chelonian, Chelodina longicollis, C. expansa and C. oblonga and from New Guinea in an unidentified freshwater chelonian. S. chelodinae differs from other species of the genus in having pseudolabia each with a blunt, prominent, cuticular projection (tooth) on the middle lobe and no other cuticular prominences, a cuticular collar without spines or protrusions, and a gubernaculum with tubes through which the spicules pass. Larvae (probably fourth-stage larvae of S. chelodinae) are also described. This is the first record of a Spiroxys sp. from the Australian Region, and from a host group (suborder Pleurodira), which has a Gondwana distribution. This is discussed in relation to the zoogeography of the genus Spiroxys and it is postulated that Australian chelids acquired this parasite from non-marine cryptodires (possibly carettochelyids or trionychids). In addition, a Spiroxys sp. is recorded from Nigeria, constituting the first such record from the Ethiopian Region. It was found in Pelusius subniger, thus constituting the second record of a Spiroxys species in a pleurodire.     

Expression ofChlamydia psittaci-encoded polypeptides inEscherichia coli

DNA fromChlamydia psittaci was partially digested with Sau 3A and cloned into the lambda bacteriophage derivative vector Charon 30. From this bank about 30 of 1500 recombinants reacted with rabbit anti-C. psittaci serum. Fourteen of these clones expressed antigens varying between 15 and 76 kilodaltons (kd) as revealed by SDS-PAGE and immunoblotting. Two recombinants, expressing 27-kd and 72-kd+76-kd antigens, respectively, were further analyzed by immunoblotting with rabbit antiserum and sera from humans with different chlamydial infections. Partial restriction endonuclease cleavage of these clones showed 10 and 13 kilobases inserts, respectively.     

Ureide Catabolism of Soybeans : II. Pathway of Catabolism in Intact Leaf Tissue

Allantoin catabolism studies have been extended to intact leaf tissue of soybean (Glycine max L. Merr.). Phenyl phosphordiamidate, one of the most potent urease inhibitors known, does not inhibit ¹⁴CO₂ release from [2,7-¹⁴C]allantoin (urea labeled), but inhibits urea dependent CO₂ release ≥99.9% under similar conditions. Furthermore, ¹⁴CO₂ and [¹⁴C] allantoate are the only detectable products of [2,7-¹⁴C]allantoin catabolism. Neither urea nor any other product were detected by analysis on HPLC organic acid or organic base columns although urea and all commercially available metabolites that have been implicated in allantoin and glyoxylate metabolism can be resolved by a combination of these two columns. In contrast, when allantoin was labeled in the two central, nonureido carbons ([4,5-¹⁴C]allantoin), its catabolism to [¹⁴C]allantoate, ¹⁴CO₂, [¹⁴C]glyoxylate, [¹⁴C]glycine, and [¹⁴C]serine in leaf discs could be detected. These data are fully consistent with the metabolism of allantoate by two amidohydrolase reactions (neither of which is urease) that occur at similar rates to release glyoxylate, which in turn is metabolized via the photorespiratory pathway. This is the first evidence that allantoate is metabolized without urease action to NH₄⁺ and CO₂ and that carbons 4 and 5 enter the photorespiratory pathway.     

Response ofPhaseolus vulgaris to inoculation withRhizobium phaseoli under two tillage systems in the dominican republic

Summary Field experiments were established at three locations in the Dominican Republic to evaluate the response of field beans (Phaseolus vulgaris L. cv. Pompadour) to inoculation with selected strains ofRhizobium phaseoli. A comparison of no-tillage and conventional tillage was included to determine whether modification of rhizosphere temperature and moisture would influence the inoculation response. Yields of inoculated treatments were not statistically difference from controls and ranged from 30–80% of those obtained on N-fertilized plots. Neither tillage systems nor P fertilization influence the response to inoculation. Serological investigations indicated that the applied rhizobial strains nodulated successfully. This host/endophyte combination appears to form an ineffective symbiotic association. Inoculation trials employing indigenous and commercial strains compared with N fertilizer in the greenhouse support the conclusion from the field studies that symbiotic N₂ fixation can provide only a fraction of the plant's N requirement.     

Whole Leaf Carbon Exchange Characteristics of Phosphate Deficient Soybeans (Glycine max L.)

Low phosphate nutrition results in increased chlorophyll fluorescence, reduced photosynthetic rate, accumulation of starch and sucrose in leaves, and low crop yields. This study investigated physiological responses of soybean (Glycine max [L.] Merr.) leaves to low inorganic phosphate (Pi) conditions. Responses of photosynthesis to light and CO₂ were examined for leaves of soybean grown at high (0.50 millimolar) or low (0.05 millimolar) Pi. Leaves of low Pi plants exhibited paraheliotropic orientation on bright sunny days rather than the normal diaheliotropic orientation exhibited by leaves of high Pi soybeans. Leaves of plants grown at high Pi had significantly higher light saturation points (1000 versus 630 micromole photons [400-700 nanometers] per square meter per second) and higher apparent quantum efficiency (0.062 versus 0.044 mole CO₂ per mole photons) at ambient (34 pascals) CO₂ than did low Pi leaves, yet stomatal conductances were similar. High Pi leaves also had significantly higher carboxylation efficiency (2.90 versus 0.49 micromole CO₂ per square meter per second per pascal), a lower CO₂ compensation point (6.9 versus 11.9 pascals), and a higher photosynthetic rate at 34 pascals CO₂ (19.5 versus 6.7 micromoles CO₂ per square meter per second) than did low Pi leaves. Soluble protein (0.94 versus 0.73 milligram per square centimeter), ribulose-1,5-bisphosphate carboxylase/oxygenase content (0.33 versus 0.25 milligram per square centimeter), and ribulose-1,5-bisphosphate carboxylase/oxygenase specific activity (25.0 versus 16.7 micromoles per square meter per second) were significantly greater in leaves of plants in the high Pi treatment. The data indicate that Pi stress alters the plant's CO₂ reduction characteristics, which may in turn affect the plant's capacity to accommodate normal radiation loads.     

Apolipoprotein E-1Harrisburg: a new variant of apolipoprotein E dominantly associated with type III hyperlipoproteinemia

Apolipoprotein E (apoE) is important in the modulation of the catabolism of chylomicron and very low density lipoprotein (VLDL) remnants. ApoE has three major genetically determined isoproteins in plasma, designated apoE-2, apoE-3 and apoE-4, with homozygosity for the allele coding for apoE-2 being associated with dysbetalipoproteinemia or type III hyperlipoproteinemia (HLP). We describe a new variant of apoE, apoE-1Harrisburg, which is, in contrast to apoE-2, dominantly associated with type III HLP. Five of twelve members of the affected kindred are heterozygous for the mutant form of apoE, and four of the five have type III HLP, while the fifth member has dysbetalipoproteinemia on diet therapy. Neuraminidase digestion, which removes charged sialic acid residues, did not alter the electrophoretic position of the apoE-1Harrisburg isoprotein, indicating that the altered charge of apoE-1Harrisburg was not due to sialic acid addition to the apolipoprotein. Cysteamine modification, which adds a positively charged group to cysteine, resulted in a shift of apoE-1Harrisburg from the E-1 to the E-2 isoform position, indicating that there is one cysteine in apoE-1Harrisburg as is the case for apoE-3. These results are consistent with apoE-1Harrisburg originating in the allele for apoE-3 with the mutation leading to a negative two-unit charge shift. The definitive identification of a kindred with an apoE variant, apoE-1Harrisburg, dominantly associated with dysbetalipoproteinemia and type III HLP provides a unique opportunity to gain important insights into the structure-function requirements of the E apolipoprotein as well as the mechanisms by which apoE modulates lipoprotein metabolism.     

Designs for synthetic case-control studies in open cohorts

Several designs are proposed for case-control studies within cohorts when the cohort is open to late entry. These and previously proposed designs are examined with respect to consistency and efficiency of relative risk parameter estimation, and a small simulation study is reported. If study costs increase in proportion to the total number of "at-risk" controls, the most efficient design, Design C, is as follows. For a case failing at time t, controls are selected at random (and without regard to "at-risk" status) from among cohort members who are (i) known not to have failed prior to t and (ii) have not been previously selected as controls. At each t, control sampling proceeds until a prespecified number of controls who are "at risk" at t have been obtained. The efficiency advantage of Design C over that of the standard case-control design proposed by Thomas (in Appendix to Liddell, McDonald, and Thomas, 1977, Journal of the Royal Statistical Society, Series B 140, 469-490) will often be small. If, on the other hand, the costs increase in proportion to the number of distinct "at-risk" controls, Design C is no longer the most efficient design. In this case, several alternative designs are proposed.     

Peak expiratory flow in symptomless elderly smokers and ex-smokers.

Values of peak expiratory flow (PEF) in 142 current smokers (116 men, 26 women) and 108 ex-smokers (88 men, 20 women) aged 55 or over were compared with the predicted values obtained in lifelong nonsmokers of the same age range. None of the subjects had been liable during childhood or subsequently to expectoration, lower respiratory tract infection, wheeze, or shortness of breath. Observed values of PEF were expressed as differences from predicted. Analysis of the relation between smoking state and ventilatory function in the men disclosed significant reductions of PEF in current smokers, the deficits increasing with the amount smoked from a mean of 48.1 l/min in those smoking fewer than 20 cigarettes a day to 73.3 l/min in smokers of 20 or more a day. Significant reductions of PEF were also found in women who were currently smoking (mean 47.4 l/min) and in male ex-smokers of 20 or more cigarettes a day (mean 27.8 l/min). There was no significant reduction of PEF in male or female ex-smokers of fewer than 20 cigarettes a day. These findings suggest that factors besides smoking are concerned in the development of irreversible airflow obstruction.