Microbially Mediated Mn(II) Oxidation in an Oligotrophic Arctic Lake

Rates of oxidation of Mn(II) were measured by an in situ incubation technique in the water column of Toolik Lake, Alaska. Measured rates were lower than those observed in other aquatic systems but were sufficient to oxidize all Mn(II) in the lake within a 3-month period. Measured rates compared favorably with rates estimated from a previous study of the geochemical cycling of Mn in Toolik Lake. The Mn(II) oxidation was largely microbially mediated, as indicated by inhibition of oxidation rates by sodium azide. Azide had been previously demonstrated to be a suitable microbial poison for studying Mn(II) oxidation in seawater. This study demonstrates that azide is also a suitable poison for freshwaters and that it inhibits microbial but not abiotic oxidation of Mn(II). Manganese(II) oxidation rates were similar during cold, under-ice conditions in early spring and during warmer summer conditions. This observation suggests that Mn(II) concentration, rather than temperature or oxygen concentration, is the most important factor regulating Mn(II) oxidation rates in Toolik Lake.     

Inactivation of gamma-aminobutyric acid aminotransferase by (Z)-4-amino-2-fluorobut-2-enoic acid

(Z)-4-Amino-2-fluorobut-2-enoic acid (1) is shown to be a mechanism-based inactivator of pig brain gamma-aminobutyric acid aminotransferase. Approximately 750 inactivator molecules are consumed prior to complete enzyme inactivation. Concurrent with enzyme inactivation is the release of 708 +/- 79 fluoride ions; transamination occurs 737 +/- 15 times per inactivation event. Inactivation of [3H]pyridoxal 5'-phosphate ([3H]PLP) reconstituted GABA aminotransferase by 1 followed by denaturation releases [3H]PMP with no radioactivity remaining attached to the protein. A similar experiment carried out with 4-amino-5-fluoropent-2-enoic acid [Silverman, R. B., Invergo, B. J., & Mathew, J. (1986) J. Med. Chem. 29, 1840-1846] as the inactivator produces no [3H]PMP; rather, another radioactive species is released. These results support an inactivation mechanism for 1 that involves normal catalytic isomerization followed by active site nucleophilic attack on the activated Michael acceptor. A general hypothesis for predicting the inactivation mechanism (Michael addition vs enamine addition) of GABA aminotransferase inactivators is proposed.     

A new subspecies and new combinations in Comarostaphylis (Ericaceae)

Comarostaphylis spinulosa subsp.glandulifera is described from the mountains of Oaxaca and Puebla, Mexico. Four new combinations inComarostaphylis are also made:C. arbutoides subsp.costaricensis, C. discolor subsp.rupestris, C. polifolia subsp.minor, andC. spinulosa.Arctostaphylos glabrata, A. rupestris, andA. spinulosa are lectotypified and the status ofC. polifolia is discussed.     

DNA sequence evidence for polymorphic forms of human serum amyloid A (SAA)

Serum amyloid A (SAA) is an acute-phase reactant and precursor to amyloid A protein, the major constituent of the fibril deposits of reactive amyloidosis. The factors determining whether the 104-amino acid SAA molecule is converted into the 76-amino acid amyloid A protein and deposited as fibrils are not known. As an initial step toward investigating the possibility that a particular primary structure of SAA is involved in amyloid formation, we have cloned and determined the nucleotide sequence of human SAA-specific cDNAs. The first clone, selected using an oligonucleotide probe, was shown to encode the signal peptide and amino-terminal region of SAA. The cDNA of this clone served as probe in the selection of two distinct, full-length SAA cDNAs, initially differentiated by the presence (pSAA21) or absence (pSAA82) of a PstI site in the coding sequence. The complete nucleotide sequence of pSAA82 cDNA was determined. Since there appear to be multiple human SAA alleles, it is conceivable that their differential expression is important to amyloid formation.     

The influence of subterranean termites on the hydrological characteristics of a Chihuahuan desert ecosystem

Summary Rainfall simulation at an average intensity of 124 mm·h^-1 was used to compare infiltration and run off on arid areas where subterranean termites had been eliminated four years prior to the initiation of the study (termite free) with adjacent areas populated by subterranean termites (termites present). Infiltration rates on termite free plots with less than 5% perennial plant cover were significantly lower 51.3±6.8 mm·h^-1 than rates on comparable termites present plots 88.4±5.6 mm·h^-1. On plots centered on Larrea tridentata shrubs, there were no differences in infiltration rates with or without termites. Plots with shrub cover had the highest infiltration rates 101±6 mm·h^-1. Highest run-off volumes were recorded from termite free <5% grass cover plots and the lowest from plots with shrubs. There were no differences in suspended sediment concentrations from termites present and termite free plots. Average bed load concentration was more than three times greater from termite free, <5% cover plots than from termites present, <5% cover plots.The reduction in infiltration, high run-off volumes and high bedloads from termite free areas without shrub cover is related to increased soil bulk density resulting from the collapse of subterranean galleries of the termites that provide avenues of bulk flow into the soil. Subterranean termites affect the hydrology of Chihuahuan desert systems by enhancing water infiltration and retention of top soil. The presence of a shrub canopy and litter layer cancels any effect of subterranean termites on hydrological parameters. Since approximately 2/3 of the area is not under shrub canopies, subterranean termites are considered to be essential for the maintenance of the soil water characteristics that support the present vegetation.     

Reaction of acetaldehyde with hemoglobin

Acetaldehyde reacted with hemoglobin at neutral pH and 37 degrees C to form adducts that were stable to dialysis and that were not reduced by sodium borohydride. Hemoglobin tetramers having 2, 3, and probably 4 molar eq of bound aldehyde were isolated by cation exchange chromatography. The sites of attachment of the aldehyde were the free amino groups of the N-terminal valine residues of the alpha and beta chains of hemoglobin. Derivatization of the beta chains caused a greater increase in the acidity of the hemoglobin than did derivatization of the alpha chains. Derivatization of the beta chains was also preferred over that of the alpha chains. Acetaldehyde derivatives of the N-terminal octapeptide of hemoglobin S (beta sT-1 peptide), Val-Gly-Gly, and tetraglycine were formed readily, contained 1 M eq of acetaldehyde/mol of peptide, and were not reduced by sodium borohydride. In contrast, Ala-Pro-Gly failed to form a 1:1 adduct with acetaldehyde. 13C NMR analysis of the peptide adducts formed with [1,2-13C]acetaldehyde indicated that tetrahedral diastereomeric derivatives were produced. The 13C chemical shifts of the adducts formed between hemoglobin and [1,2-13C]acetaldehyde were identical to those of the peptide adducts although resonances from the individual diastereomeric adducts at each hemoglobin site could not be resolved. The results cited above as well as other evidence indicate that acetaldehyde reacts with the amino termini of hemoglobin to form stable cyclic imidazolidinone derivatives. An exchange of acetaldehyde residues between peptides was also documented.     

Polyester Wadding for Specimen Orientation During Embedding in Methacrylates

Polyester fibers are not dissolved by either glycol methacrylate or methyl methacrylate. Commercial polyester wadding is consequently an advantageous material to use in getting precise orientation of tissue specimens during embedding in methacrylate.     

Evolution of karyotypic abnormalities and C-MYC oncogene amplification in human colonic carcinoma cell lines

Cell lines (COLO 320 DM and COLO 320 HSR), established from a human neuroendocrine tumor, contain an amplified cellular oncogene (c-myc). We have previously shown that the homogeneously staining regions (HSRs) of a marker chromosome in the COLO 320 HSR cells that evolved in culture from COLO 320 DM cells contain amplified c-myc. Molecular hybridization in situ has now been used to demonstrate that the HSRs are on both arms of what was once an X chromosome. We also show that amplified c-myc copies are present in the isolated double minute chromosomes (DMs) of the COLO 320 DM cells that were characteristic of the tumor cells initially established from the patient. The results suggest that the amplified c-myc appeared first as DMs and was subsequently transposed to engender HSRs on an X chromosome. The initial COLO 320 tumor cell may have acquired two early replicating (i.e., active) X chromosomes and lost the late replicating (i.e., inactive) X.     

Radiosensitivity of peripheral blood lymphocytes in autoimmune disease

The proliferation of peripheral blood lymphocytes, cultured with Con A, can be inhibited by ionizing radiation. Lymphocytes from patients with conditions associated with autoimmunity, such as rheumatoid arthritis, systemic lupus erythematosus and polymyositis, are more radiosensitive than those from healthy volunteers or patients with conditions not associated with autoimmunity. The nuclear material isolated from the lymphocytes of patients with autoimmune diseases is, on average, lighter in density than the nuclear material from most healthy controls. This difference in density is not related to increased sensitivity to ionizing radiation but the degree of post-irradiation change in density (lightening) is proportional to the initial density, i.e. more dense nuclear material always shows a greater upward shift after radiation. The recovery of preirradiation density of nuclear material, 1 h after radiation exposure, taken as an indication of DNA repair, correlates with the radiosensitivity of lymphocyte proliferation (Con A response); failure to return to pre-irradiation density being associated with increased sensitivity of proliferative response. These results require extension but, taken with previously reported studies of the effects of DNA methylating agents, support the idea that DNA damage and its defective repair could be important in the aetio-pathogenesis of autoimmune disease.