The nitrogen cycle in lodgepole pine forests,southeastern Wyoming

Storage and flux of nitrogen were studied in several contrasting lodgepole pine (Pinus contorta spp.latifolia) forests in southeastern Wyoming. The mineral soil contained most of the N in these ecosystems (range of 315–860 g · m^–2), with aboveground detritus (37.5–48.8g · m^–2) and living biomass (19.5–24.0 g · m^–2) storing much smaller amounts. About 60–70% of the total N in vegetation was aboveground, and N concentrations in plant tissues were unusually low (foliage = 0.7% N), as were N input via wet precipitation (0.25 g · m^–2 · yr^–1), and biological fixation of atmospheric N (<0.03 g · m^–2 · yr^–1, except locally in some stands at low elevations where symbiotic fixation by the leguminous herbLupinus argenteus probably exceeded 0.1 g · m^–2 · yr^–1).Because of low concentrations in litterfall and limited opportunity for leaching, N accumulated in decaying leaves for 6–7 yr following leaf fall. This process represented an annual flux of about 0.5g · m^–2 to the 01 horizon. Only 20% of this flux was provided by throughfall, with the remaining 0.4g · m^–2 · yr^–1 apparently added from layers below. Low mineralization and small amounts of N uptake from the 02 are likely because of minimal rooting in the forest floor (as defined herein) and negligible mineral N (< 0.05 mg · L^–1) in 02 leachate. A critical transport process was solubilization of organic N, mostly fulvic acids. Most of the organic N from the forest floor was retained within the major tree rooting zone (0–40 cm), and mineralization of soil organic N provided NH₄ for tree uptake. Nitrate was at trace levels in soil solutions, and a long lag in nitrification was always observed under disturbed conditions. Total root nitrogen uptake was calculated to be 1.25 gN · m^–2 · yr^–1 with estimated root turnover of 0.37-gN · m^–2 · yr^–1, and the soil horizons appeared to be nearly in balance with respect to N. The high demand for mineralized N and the precipitation of fulvic acid in the mineral soil resulted in minimal deep leaching in most stands (< 0.02 g · m^–2 · yr^–1). These forests provide an extreme example of nitrogen behavior in dry, infertile forests.     

Inhibition of class C beta-lactamases by (1''R,6R)-6-(1''-hydroxy)benzylpenicillanic acid SS-dioxide.

beta-Lactamases, enzymes that catalyse the hydrolysis of the beta-lactam ring in beta-lactam antibiotics, are divided into three classes, A, B and C, on the basis of the structures so far determined. There are relatively few effective inhibitors of class C beta-lactamases. A beta-lactam sulphone with a hydroxybenzyl side chain, namely (1'R,6R)-6-(1'-hydroxy)benzylpenicillanic acid SS-dioxide (I), has now been studied. The sulphone is a good mechanism-based inhibitor of class C beta-lactamases. At pH8, the inhibition of a Pseudomonas beta-lactamase is irreversible, and proceeds at a rate that is about one-tenth the rate of concurrent hydrolysis. The labelled enzyme has enhanced u.v. absorption and is probably an enamine. At a lower pH, however, inhibition is transitory.     

Fibrinogen Manchester. Detection of a heterozygous phenotype in the intraplatelet pool.

Family members heterozygous for the congenitally abnormal fibrinogen designated fibrinogen Manchester, A alpha 16Arg----His, have previously been shown by h.p.l.c. and amino acid analysis to release a variant fibrinopeptide, [His16]fibrinopeptide A, from plasma fibrinogen after the addition of thrombin. The present study was designed to determine if the same abnormal phenotype was also present in the intraplatelet fibrinogen pool. Fresh platelets were washed in buffers containing EDTA until it could be shown that all washable plasma fibrinogen was removed. Normal platelets were then lysed by freezing and thawing to release their intracellular proteins, which were then treated with thrombin. The fibrinopeptides, cleaved from the intraplatelet fibrinogen, could be detected by an optimized h.p.l.c. technique. Quantification of the intraplatelet fibrinogen gave a result (means +/- S.D., n = 5) of 110 +/- 30 and 90 +/- 30 micrograms/10(9) platelets, when determined by h.p.l.c. quantification of fibrinopeptide B content and fibrinogen fragment E radioimmunoassay respectively. Examination of fibrinopeptides released from the platelet fibrinogen from the family with fibrinogen Manchester with the same techniques showed elution peaks in the same positions as both [His16]fibrinopeptide A and normal fibrinopeptide A. The identity of these peaks was further substantiated by analysis of the h.p.l.c. peaks by using specific radioimmunoassay to fibrinopeptide A. Our results therefore demonstrate that platelet fibrinogen expresses the heterozygous A alpha 16His phenotype. This supports the view that the A alpha chains of platelet and plasma fibrinogen are produced from a single genetic locus.     

Biosynthesis and processing of legumin-like storage proteins in Lupinus angustifolius (lupin).

Synthesis, secretion and post-translational proteolysis of the storage proteins in cotyledons of Lupinus angustifolius L. (lupin) have been examined in vivo and in vitro by using a combination of pulse-chase experiments with [3H]- or [35S]-labelled amino acids, subcellular fractionation and cell-free translation from poly(A)+ (polyadenylylated) RNA or membrane-bound polyribosomes. Related polypeptides were identified by immunoprecipitation, separation on sodium dodecyl sulphate/polyacrylamide gels and fluorography. The synthesis and processing of two proteins were compared. Conglutin alpha, the 11 S protein, was found as a family of precursor polypeptides of Mr 68000-88000 when translated from poly(A)+ RNA under conditions where signal segments were not cleaved, and Mr 64000-85000 both when sequestered into the endoplasmic reticulum and when accumulated in the protein bodies. Pulse-chase labelling showed that cotyledons from early stages of development were completely incapable of further proteolysis of these precursors. Nevertheless, in the same juvenile cotyledons, the precursors of the minor storage protein conglutin gamma, two polypeptides with Mr 50000-51000, were proteolytically cleaved to mature subunits of Mr 32000 and 17000 within 2 h. Further cleavage of the precursors of conglutin alpha into families of mature subunits of Mr 21000-24000 and 42000-62000 was detected in more mature cotyledons. A model is proposed which suggests that the mature subunits are produced by a single proteolytic cleavage of each of the three major precursors of conglutin alpha and also suggests that a close similarity exists between these subunits and those of other legumin-like proteins. The enzyme responsible for this cleavage, which appears at a specific stage in the middle of cotyledonary development, seems to be an integral part of the programmed developmental sequence in these pods.     

Interferon-induced proteins. Purification and characterization of a 15,000-dalton protein from human and bovine cells induced by interferon

Human interferons induce a protein of 15,000 daltons in human and bovine cells. This protein is located in the cytoplasm in a soluble form and is induced by concentrations of interferon which induce the antiviral state. Messenger RNA prepared from interferon-treated human and bovine cells contains a mRNA which yields on translation in vitro a protein similar in size to the 15-kDa protein induced by interferon in vivo. The human protein has been purified to homogeneity from interferon-treated human cells by ion-exchange chromatography and reverse-phase high-performance liquid chromatography. A comparison of the peptides generated by V8 protease from the human and bovine 15-kDa proteins reveals that the two proteins are similar but not identical.     

Effect of age and training on aerobic capacity and body composition of master athletes

Maximum oxygen uptake (VO2max) and body composition have been shown to deteriorate with age. How much of the decline is attributable to aging and how much is affected by reduced physical activity is not known. The purpose of this investigation was to determine the aerobic capacity and body composition of 24 master track athletes and to evaluate the relationship to age and maintenance of training over a 10-yr period. The subjects (50-82 yr of age) were retested after a 10.1-yr follow-up (T2). All continued their aerobic training, but only 11 were still highly competitive (COMP) and continued to train at the same intensity. The other 13 athletes studied became noncompetitive (post-COMP) and reduced their training intensity. The results showed the COMP group to maintain its VO2max and maximum O2 pulse while the post-COMP group showed a significant decline (54.2-53.3 vs. 52.5-45.9 ml X kg-1 X min-1; 20.7-20.8 vs. 22.4-20.0 ml/beat from test one (T1) to T2 for the COMP vs. post-COMP groups, respectively). Maximum heart rate declined 7 beats/min for both groups. Body composition showed no difference between groups from T1 to T2. For both groups body weight declined slightly (70.0-68.9 kg), percent fat increased significantly (13.1-15.1%), and fat-free weight decreased significantly (61.0-59.0 kg). Thus, when training was maintained, aerobic capacity remained unchanged over the follow-up period. Body composition changed for both groups and may have been related to aging and/or the type of training performed.     

Major polypeptide of duck hepatitis B surface antigen particles

The 40- to 50-nm pleomorphic particles found in the sera of domestic Pekin ducks infected with duck hepatitis B virus were purified by rate zonal and isopycnic centrifugation. Sodium dodecyl sulfate-polyacrylamide gel electrophoretic polypeptide analysis of these particles, called duck hepatitis B surface antigen particles, revealed the major component to be a single 17,500-dalton polypeptide. This result is in contrast to polypeptide analyses of the surface antigens of related mammalian viruses, including hepatitis B, in which a major doublet of polypeptides is seen with molecular weights ranging from 23,000 to 29,000. Tryptic maps of 17,500-dalton polypeptide resembled that of the major non-glycosylated polypeptide of the adw subtype of hepatitis B surface antigen. A serological assay for antibody to the purified duck virus particles is also described.     

Cloned nodulation genes of Rhizobium leguminosarum determine host-range specificity

Summary Three nodulation-deficient (nod) mutants of Rhizobium leguminosarum were isolated following insertion of the transposon Tn5 into pRL1JI, the R. leguminosarum plasmid known to carry the nodulation genes. DNA adjacent to the nod: Tn5 alleles was subcloned and used to probe a cosmid clone bank containing DNA from a Rhizobium strain carrying pRL1JI. Two cosmid clones which showed homology with the probe contained about 10 kb of DNA in common. The R. leguminosarum host-range determinants were found to be present within this 10 kb common region since either of the cosmid clones could enable a cured R. phaseoli strain to nodulate peas instead of Phaseolus beans, its normal host. Electron microscopy of nodules induced by Rhizobium strains cured of their normal symbiotic plasmid but containing either of the two cosmid clones showed bacteroid-forms surrounded by a peri-bacteroid membrane, indicating that normal infection had occurred. Thus it is clear that this 10 kb region of nodDNA carries the genes that determine host range and that relatively few bacterial genes may be involved in nodule and bacteroid development.