Nitrogen dynamics in a eutrophic lake sediment

Nitrogen flux from sediment of a shallow lake and subsequent utilization by water hyacinth (Eichhornia crassipes [Mart] Solms) present in the water column were evaluated using an outdoor microcosm sediment-water column. Sediment N was enriched with ¹⁵N to quantitatively determine the movement of NH₄-N from the sediment to the overlying water column. During the first 30 days. 48% of the total N uptake by water hyacinth was derived from sediment ¹⁵NH₄-N. This had decreased to 14% after 183 days. Mass balance of N indicates that about 25% sediment NH₄-N was released into the overlying water, but only 17% was assimilated by water hyacinth. NH₄-N levels in the water column were very low, with very little or no concentration gradients. NH₄-N levels in the interstitial water of the sediment were in the range of 30–35 mg L^–1 for the lower depths (> 35 cm), while in the surface 5 cm of depth NH₄-N levels decreased to 3.2 mg L^–1. Simulated results also showed similar trends for the interstitial NH₄-N concentration of the sediment. The overall estimated NH₄-N flux from the sediment to the overlying water was 4.8 µg cm^–2 day^–1, and the soluble organic N flux was 5.8 µg N cm^–2 day^–1. Total N flux was 10.6 µg N cm^–2 day^–1.     

Identification of a new glutathione S-transferase from rat liver cytosol

A new glutathione $\text{S}$-transferase has been purified to homogeneity from 105,000 × g supernatant of Sprague-Dawley rat liver homogenates. The purified enzyme exhibited specific activities of approximately 1.8, and 0.12 μmoles. min^?1. mg^?1 toward 1-chloro 2,4-dinitrobenzene and cumene hydroperoxide respectively. The SDS gel electrophoresis data on subunit composition revealed that the new transferase is composed of two subunits with an identical M_r of 24,400 (Y_α Family). Our $\text{in}\text{vitro}$ translation experiments with rat liver poly(A) RNAs and substrate specificity data suggest that this subunit is different from the previously reported Ya, Yb and Yc subunits of rat liver glutathione $\text{S}$-transferases. Comparatively, the new isozyme showed significant activity toward 1,2 epoxy-3-(P-nitrophenoxy)-propane, ethacrynic acid and P-nitrophenyl acetate, 0.4, 0.34 and 0.18 μ moles. min^?1. mg^?1 respectively.     

Tunicamycin suppresses differentiation and stimulates dedifferentiation of heterocysts in the cyanobacteriumAnabaena azollae Stras

The effect of tunicamycin (TM), a specific inhibitor of glycosylation of proteins, on heterocyst differentiation inAnabaena azollae Stras. was investigated. Heterocysts were developed in the presence of TM up to a concentration of 0.2 g ml^–1, whereas at higher concentrations differentiation proceeded only up to the proheterocyst stage. Analysis of lipids by thinlayer chromatography showed that the glycolipid that is specific for the laminated layer of mature heterocysts was synthesized even in the cultures where the differentiation had proceeded only up to the early proheterocyst stage (i.e., at>0.2 g TM ml^–1). Further, deposition of the glycolipid-containing laminated layer in the envelope of the heterocysts differentiated in the presence of TM (i.e., at 0.2 g ml^–1) was incohesive as observed at the ultrastructural level. These findings clearly suggest that the process leading to the transportation of the heterocyst-specific glycolipid and its deposition as a laminated layer are affected by TM treatment. Because of the reported highly selective mode of action of TM, our results implicate a role for protein glycosylation in the process of heterocyst development and maturation.Although the heterocyst is a terminal stage of differentiation, because they normally do not divide/multiply, a considerable percentage of heterocysts that developed in the presence of TM dedifferentiated. The aberrations formed in the laminated layer, probably because of the inhibition of protein glycosylation owing to TM treatment, may have contributed to the instability of heterocyst structure and consequently led to their dedifferentiation.     

Amino acid substitutions in the human glutathione S-transferases confer different specificities in the prostaglandin endoperoxide conversion pathway

The human glutathione S-transferases 1-1 and 2-2, which differ from each other by 11 amino acids, have different catalytic activities against cumene hydroperoxide and t-butyl hydroperoxide. Using prostaglandin H2 as the peroxide substrate, we found that GSH S-transferase 1-1 catalyzed the transformation of prostaglandin H2 to prostaglandin F2 alpha and E2 at a 4:1 ratio whereas GSH S-transferase 2-2 produced primarily prostaglandin D2 and F2 alpha at a 4:1 ratio. Our results indicate that GSH S-transferases catalyze the reduction and isomerization of prostaglandin H2 endoperoxide in vitro. We suggest that the amino acid substitutions between these two isozymes may be responsible for the difference in catalytic specificities. We propose that these isozymes are important reagents for the biosynthesis of various prostaglandins.     

Cloning and expression of a human muscle phosphofructokinase cDNA

The nucleotide sequence of a 2.86-kb cDNA clone containing the complete human muscle phosphofructokinase (PFK) protein-coding region was determined. It comprises 76 bp of 5'-untranslated sequence, 2340 bp encoding human muscle PFK polypeptide, and 399 bp of 3'-untranslated sequence plus a poly(A) tract. A retroviral vector was utilized to express the product of this coding sequence in mouse fibroblasts. The PFK-coding cDNA was shown to code for an enzymatically active polypeptide by immunoprecipitation analysis and DEAE-Sephadex A-25 chromatography.     

In vitro effects of gossypol and lactic acid on rat uterus and ovary during implantation and antiimplantation

ATPase activity of uterus and ovary was markedly elevated in presence of gossypol and decreased in presence of lactic acid indicating activation and inhibition of energy metabolism by gossypol and lactic acid respectively. The elevated levels of glycogen in uterus indicate inhibition of glycogenolysis as supported by phosphorylase activity. Whereas in ovary the glycogen depletion indicates activation of glycogenolysis supported by phosphorylase activity. The activity levels of aldolase and G-6-PDH decreased in the uterus in presence of gossypol and increased in presence of lactic acid. The same were elevated in ovary indicating the activation of hexose mono and diphosphate pathways. Lactic acid accumulated in presence of both gossypol and lactic acid with a depletion in level of pyruvic acid in both the tissues. This situation in the uterus indicates the condition of anti-implantation in presence of both gossypol and lactic acid. The NAD-LDH activity was inhibited in presence of gossypol and activated in presence of lactic acid in both tissues.     

Multiple chromosomes of Azotobacter vinelandii.

The number of copies of the genes leuB, nifH, nifD, and nifK per cell of Azotobacter vinelandii has been determined to be about 80. A beta-lactamase gene was integrated into the A. vinelandii chromosome by single-point crossover. Subsequently, we have been able to detect nearly 80 copies of this beta-lactamase gene per cell of A. vinelandii when cultured for a large number of generations in the presence of ampicillin. The multiple copies of the beta-lactamase gene do not seem to be present on a single chromosome, as evident from the fragment obtained by digestion of cellular DNA with the appropriate restriction endonuclease. The kinetics of renaturation of DNA of A. vinelandii is suggestive of complexity similar to that of Escherichia coli. The DNA content of A. vinelandii, however, is 40 times that of E. coli. All these indicate the presence of multiple chromosomes, possibly as many as 80, in A. vinelandii.     

Rat nucleolar 7-2 RNA is homologous to mouse mitochondrial RNase mitochondrial RNA-processing RNA

7-2 RNA (also termed RNA M and 7SM RNA) is a noncapped small RNA present in small ribonucleoprotein particles; these particles are present in the granular compartment of the nucleolus. Some sera from patients with scleroderma specifically immunoprecipitate 7-2 RNA-containing particles (Hashimoto, C., and Steitz, J. A. (1983) J. Biol. Chem. 258, 1379-1382; Reddy, R., Tan, E. M., Henning, D., Nohga, K., and Busch, H. (1983) J. Biol. Chem. 258, 1383-1386; Reimer, G., Raska, I., Scheer, U., and Tan, E.M. (1988) Exp. Cell Res. 176, 117-128). In this study, the primary sequence of Novikoff hepatoma 7-2 RNA was determined and a possible secondary structure is presented. The Novikoff hepatoma 7-2 RNA is 94% homologous to the recently described mouse mitochondrial RNase MRP RNA, suggesting that Novikoff hepatoma 7-2 RNA may be the homologue of mouse MRP RNA. The presence of 7-2 RNA in nucleoli and in mitochondria suggests that 7-2 ribonucleoproteins, in addition to being essential components of mitochondrial RNase, may also be functional in nucleolar RNA processing and ribosome biogenesis.     

Purification and characterization of Cu-Zn superoxide dismutases from mungbean (Vigna radiata) seedlings

Mungbean contains three isoenzymes of superoxide dismutase designated isoenzyme I, II and III. The two cytosolic superoxide dismutases (I and II) were purified to homogeneity by ammonium sulphate fractionation, ion exchange chromatography on diethylaminoethyl cellulose, gel filtration and preparative polyacrylamide.gel electrophoresis. The molecular weights of isoenzyme I and isoenzyme II were determined to be 33,000 and 31,600 respectively. The subunit molecular weight was approximately 16,000 indicating that the isoenzymes contained two identical subunits. The ultra-violet absorption spectra revealed a maximum at 258–264 nm for the two isoenzymes. Superoxide dismutase I and II were inhibited to different extents by metal chelators. Isoenzyme I was more sensitive to inhibition by cyanide and azide, while isoenzyme II was more susceptible to inhibition by diethyldithiocarbamate ando-phenanthroline. Both the isoenzymes exhibited similar denaturation profiles with heat, guanidinium chloride and urea. The denaturation with urea and guanidinium chloride was reversible. The two copper-zinc enzymes were more stable towards thermal inactivation compared to manganese and iron superoxide dismutases from other sources. The results indicate that the two isoenzymes differ from each other only with respect to charge and sensitivity towards metal chelators.