Notes on the genus Pteroceras (Orchidaceae)

A new name (Pteroceras semiteretifolium H. Æ. Peders.) and two new combinations (P. cladostachyum (Hook.f.) H. Æ. Peders., P. unguiculatum (Lindley) H. Æ. Peders.) are presented. The correct application of the name P. pallidum (Blume) Holttum is discussed.     

Quaternary structure of ATP synthases: Symmetry and asymmetry in the F1 moiety

It has been proposed that during ATP synthesis/hydrolysis F₁ ATPases experience a complex pattern of nucleotide binding and release during the catalytic cycle (binding change mechanism). This type of mechanism has implications that can be correlated with the structure of the enzyme. F₁-ATPases (stoichiometry ₃₃) are essentially a symmetrical trimer of pairs of the major subunits ( and ); the minor subunits (, and ) are in single copies and interact with the trimer in an asymmetrical fashion. The asymmetry introduced by the minor subunits has important structural and functional consequences: (1) it introduces differences between the potentially equivalent binding and catalytic sites in the major subunits, (2) it restricts the ways in which a binding change mechanism can occur, and (3) it governs the way in which the F₁ interacts with the (asymmetrical) F₀ sector.     

Hexokinase receptors: Preferential enzyme binding in normal cells to nonmitochondrial sites and in transformed cells to mitochondrial sites

Hexokinase plays an important role in normal glucose-utilizing tissues like brain and kidney, and an even more important role in highly malignant cancer cells where it is markedly overexpressed. In both cell types, normal and transformed, a significant portion of the total hexokinase activity is bound to particulate material that sediments upon differential centrifugation with the crude mitochondrial fraction. In the case of brain, particulate binding may constitute most of the total hexokinase activity of the cell, and in highly malignant tumor cells as much as 80 percent of the total. When a variety of techniques are rigorously applied to better define the particulate location of hexokinase within the crude mitochondrial fraction, a striking difference is observed between the distribution of hexokinase in normal and transformed cells. Significantly, particulate hexokinase found in rat brain, kidney, or liver consistently distributes with nonmitochondrial membrane markers whereas the particulate hexokinase of highly glycolytic hepatoma cells distributes with outer mitochondrial membrane markers. These studies indicate that within normal tissues hexokinase binds preferentially to non-mitochondrial receptor sites but upon transformation of such cells to yield poorly differentiated, highly malignant tumors, the overexpressed enzyme binds preferentially to outer mitochondrial membrane receptors. These studies, taken together with the well-known observation that, once solubilized, the particulate hexokinase from a normal tissue can bind to isolated mitochondria, are consistent with the presence in normal tissues of at least two different types of particulate receptors for hexokinase with different subcellular locations. A model which explains this unique transformation-dependent shift in the intracellular location of hexokinase is proposed.     

The effect of cytoplasmic K+ on the activity of the Na+/K(+)-ATPase.

Experiments with the reconstituted (Na+ + K+)-ATPase show that besides the ATP-dependent cytoplasmic Na(+)-K+ competition for Na+ activation there is a high affinity inhibitory effect of cytoplasmic K+. In contrast to the high affinity K+ inhibition seen with the unsided preparation at a low ATP especially at a low temperature, the high affinity inhibition by cytoplasmic K+ does not disappear when the ATP concentration an-or the temperature is increased. The high affinity inhibition by cytoplasmic K+ is also observed with Cs+, Li+ or K+ as the extracellular cation, but the fractional inhibition is much less pronounced than with Na+ as the extracellular cation. The results suggest that either there are two populations of enzyme, one with the normal ATP dependent cytoplasmic Na(+)-K+ competition, and another which due to the preparative procedure has lost this ATP sensitivity. Or that the normal enzyme has two pathways for the transition from E2-P to E1ATP. One on which the enzyme with the translocated ion binds cytoplasmic K+ with a high affinity but not ATP, and another on which ATP is bound but not K+. A kinetic model which can accommodate this is suggested.     

Mineralization of 2,4-dichlorophenoxyacetic acid (2,4-D) in soil inoculated with Pseudomonas cepacia DBO1(pRO101), Alcaligenes eutrophus AEO106(pRO101) and Alcaligenes eutrophus JMP134(pJP4): effects of inoculation level and substrate concentration

Mineralization of 2,4-dichlorophenoxyacetic acid (2,4-D) by two Alcaligenes eutrophus strains and one Pseudomonas cepacia strain containing the 2,4-D degrading plasmids pJP4 or pRO101 (=pJP4::Tn1721) was tested in 50 g (wet wt) samples of non-sterile soil. Mineralization was measured as ¹⁴C-CO₂evolved during degradation of uniformly-ring-labelled ¹⁴C-2,4-D. When the strains were inoculated to a level of approximately 10⁸ CFU/g soil, between 20 and 45% of the added 2,4-D (0.05 ppm, 10 ppm or 500 ppm) was mineralized within 72 h. Mineralization of 0.05 ppm and 10 ppm, 2,4-D by the two A. eutrophus strains was identical and rapid whereas mineralization by P. cepacia DBO1(pRO101) occurred more slowly. In contrast, mineralization of 500 ppm 2,4-D by the two A. eutrophus strains was very slow whereas mineralization by P. cepacia DBO1 was more rapid. Comparison of 2,4-D mineralization at different levels of inoculation with P. cepacia DBO1(pRO101) (6×10⁴, 6×10⁶ and 1×10⁸ CFU/g soil) revealed that the maximum mineralization rate was reached earlier with the high inoculation levels than with the low level. The kinetics of mineralization were evaluated by nonlinear regression analysis using five different models. The linear or the logarithmic form of a three-half-order model were found to be the most appropriate models for describing 2,4-D mineralization in soil. In the cases in which the logarithmic form of the three-half-order model was the most appropriate model we found, in accordance with the assumptions of the model, a significant growth of the inoculated strains.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - CFU colony forming units - PTYG peptone, tryptone, yeast & glucose - DPM disintegrations per minute     

A novel function of the cAMP-CRP complex in Escherichia coli: cAMP-CRP functions as an adaptor for the CytR repressor in the deo operon

Unlike classical bacterial repressors, the CytR repressor of Escherichia coli cannot independently regulate gene expression. Here we show that CytR binding to the deoP2 promoter relies on interaction with the master gene regulatory protein, CRP, and, furthermore, that cAMP-CRP and CytR bind co-operatively to deoP2. Using mutant promoters we show that tandem, properly spaced DNA-bound cAMP-CRP complexes are required for this co-operative binding. These data suggest that CytR forms a bridge between tandem cAMP-CRP complexes, and that cAMP-CRP functions as an adaptor for CytR. The implications of this new version of negative control in E. coli on bacterial gene expression and on combinatorial gene regulation in higher organisms are discussed.     

Transfer of Lactic Acid Bacterial Strains from the Feed to the Sow,the Environment,and the Piglets

The spread of lactic acid bacterial strains to the environment and to newborn piglets was investigated after feeding of such strains to sows. Rifampicin resistant bacterial strains were fed to sows, 1010 c.f.u. per day, during the period from 1 week before expected farrowing until 1 week after farrowing. Fecal samples from the sows and samples of litter were collected for bacteriological examination together with swabs from the pens, the skin of the sows, and from the rectum of the piglets. The test strains were only excreted in relatively low amounts in the feces of the sows, approximately 103 −106 c.f.u. per gram. They were not able to displace the normal lactic acid bacterial flora in the sows nor were they transmitted to the intestinal tract of the piglets to any significant extent. After the last administration the test strains disappeared from both feces, skin, and environment, indicating that no permanent colonization had taken place, although considerable differences in duration of persistence were noticed between test strains.     

Immunocytochemical identification of the human α2-macrogiobulin receptor in monocytes and fibroblasts: Monoclonal antibodies define the receptor as a monocyte differentiation antigen

The α₂-macroglobulin receptor was recently purified from rat liver and human placenta. Three different monoclonal antibodies have now been raised against the human receptor and expression of the 440-kDa receptor protein is demonstrated in human placenta, fibroblasts, liver, and monocytes by immunoblot analysis. Flow cytometric studies showed that anti-α₂-macroglobulin receptor monoclonal antibodies bind to 90–100% of the blood monocyte population and not to other blood cells. This defines the α₂-macroglobulin receptor as a monocyte differentiation antigen, different from any of the classified leucocyte cluster determinants. Electron microscopic gold immunocytochemistry revealed the subcellular distribution of the receptor in human cultured monocytes and fibroblasts. In these cells, 18–33% of the gold particles were found on the outside of the plasma membrane, and in fibroblasts, especially, in coated invaginations. The intracellular receptors were mainly distributed in vesicles and tubular structures.     

A 21S enzyme complex from HeLa cells that functions in simian virus 40 DNA replication in vitro

A sedimentable complex of enzymes for DNA synthesis was partially purified from the combined low-salt nuclear extract-postmicrosomal supernatant solution of HeLa cell homogenates by poly(ethylene glycol) precipitation in the presence of 2 M KCl, discontinuous gradient centrifugation, Q-Sepharose chromatography, and velocity gradient centrifugation. In addition to the previously described 640-kDa multiprotein DNA polymerase alpha-primase complex [Vishwanatha et al. (1986) J. Biol. Chem. 261, 6619-6628], the enzyme complex also has associated topoisomerase I, DNA-dependent ATPase, RNase H, DNA ligase, a simian virus 40 origin recognition, dA/dT sequence binding protein [Malkas & Baril (1989) Proc. Natl. Acad. Sci. U.S.A. 86, 70-74], and proliferating cell nuclear antigen. Essentially all of the T antigen dependent simian virus 40 in vitro replication activity in the combined nuclear extract-postmicrosomal supernatant solution resides with the sedimentable complex of enzymes for DNA synthesis. Sedimentation analysis on a 10-35% glycerol gradient in the presence of 0.5 M KCl indicates that the enzyme complex is 21S. The associated enzymes for DNA synthesis and in vitro simian virus 40 replication activity cofractionate throughout the purification of the 21S complex. The DNA polymerase and in vitro simian virus 40 replication activities are both inhibited by monoclonal antibody (SJK 132-20) to human DNA polymerase alpha and by 5-10 microM butylphenyl-dGTP, indicating that the association of DNA polymerase alpha with the 21S enzyme complex is essential for the initiation of SV40 DNA replication in vitro.