Primary structure of kunitz-type trypsin inhibitor-2a (pI 5.9) fromPsophocarpus tetragonolobus (L.) DC seed

The primary structure of acidic trypsin inhibitor-2a (WBTI-2a,pI 5.9) fromPsophocarpus tetragonolobus (L.) DC seed was determined. This inhibitor consists of a single polypeptide chain of 180 amino acids including four half-cystine residues and has an N-terminal residue of pyroglutamic acid. The sequence of WBTI-2a,pI 5.9, showed 84% identity to acidic trypsin inhibitor-2 (WBTI-2,pI 5.1) but only 57% identity to the basic trypsin inhibitor (WBTI-1,pI 8.9) and 50% identity to the chymotrypsin inhibitor of winged bean. The data indicate that winged bean seed contains a family of three Kunitz-type inhibitors which have about 50% identity.     

Ice Nucleation Induced by Pseudomonas syringae

Broth cultures of suspensions of Pseudomonas syringae isolated from decaying alder leaves (Alnus tenuifolia) were found to freeze at very warm (-1.8 to -3.8 C) temperatures. The initiation of freezing appears associated with the intact cell and not with extracellular material. Chemical treatments and physical destruction of the cell destroy activity. Bacteria must be in concentrations of approximately 10(6)/ml before freezing at warm temperatures occurs.     

Purification of Mitochondrial Glutamate Dehydrogenase from Dark-Grown Soybean Seedlings

Proteins in extracts from cotyledons, hypocotyls, and roots of 5-d-old, dark-grown soybean (Glycine max L. Merr. cv Williams) seedlings were separated by polyacrylamide gel electrophoresis. Three isoforms of glutamate dehydrogenase (GDH) were resolved and visualized in gels stained for GDH activity. Two isoforms with high electrophoretic mobility, GDH1 and GDH2, were in protein extracts from cotyledons and a third isoform with the lowest electrophoretic mobility, GDH3, was identified in protein extracts from root and hypocotyls. Subcellular fractionation of dark-grown soybean tissues demonstrated that GDH3 was associated with intact mitochondria. GDH3 was purified to homogeneity, as determined by native and sodium dodecyl sulfate-polyacrylamide gels. The isoenzyme was composed of a single 42-kD subunit. The pH optima for the reductive amination and the oxidative deamination reactions were 8.0 and 9.3, respectively. At any given pH, GDH activity was 12- to 50-fold higher in the direction of reductive amination than in the direction of the oxidative deamination reaction. GDH3 had a cofactor preference for NAD(H) over NADP(H). The apparent Michaelis constant values for [alpha]-ketoglutarate, ammonium, and NADH at pH 8.0 were 3.6, 35.5, and 0.07 mM, respectively. The apparent Michaelis constant values for glutamate and NAD were 15.8 and 0.10 mM at pH 9.3, respectively. To our knowledge, this is the first biochemical and physical characterization of a purified mitochondrial NAD(H)-dependent GDH isoenzyme from soybean.     

Oligomeric complexes formed by Redβ single strand annealing protein in its different DNA bound states

Redβ is a single strand annealing protein from bacteriophage λ that binds loosely to ssDNA, not at all to pre-formed dsDNA, but tightly to a duplex intermediate of annealing. As viewed by electron microscopy, Redβ forms oligomeric rings on ssDNA substrate, and helical filaments on the annealed duplex intermediate. However, it is not clear if these are the functional forms of the protein in vivo. We have used size-exclusion chromatography coupled with multi-angle light scattering, analytical ultracentrifugation and native mass spectrometry (nMS) to characterize the size of the oligomers formed by Redβ in its different DNA-bound states. The nMS data, which resolve species with the highest resolution, reveal that Redβ forms an oligomer of 12 subunits in the absence of DNA, complexes ranging from 4 to 14 subunits on 38-mer ssDNA, and a much more distinct and stable complex of 11 subunits on 38-mer annealed duplex. We also measure the concentration of Redβ in cells active for recombination and find it to range from 7 to 27 μM. Collectively, these data provide new insights into the dynamic nature of the complex on ssDNA, and the more stable and defined complex on annealed duplex.     

18S rRNA data indicate that Aschelminthes are polyphyletic in origin and consist of at least three distinct clades

The Aschelminthes is a collection of at least eight animal phyla, historically grouped together because the absence of a true body cavity was perceived as a pseudocoelom. Analyses of 18S rRNA sequences from six Aschelminth phyla (including four previously unpublished sequences) support polyphyly for the Aschelminthes. At least three distinct groups of Aschelminthes were detected: the Priapulida among the protostomes, the Rotifera-Acanthocephala as a sister group to the protostomes, and the Nematoda as a basal group to the triploblastic Eumetazoa.      

Pathway for the formation of D-3 phosphate containing inositol phospholipids in intact human platelets

We have identified the structure of phosphatidylinositol 3-phosphate (PtdIns(3)P), phosphatidylinositol 3,4-bisphosphate (PtdIns(3,4)P2) and phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P3) in human platelets. These lipids accounted for less than 2% of the total 32P incorporated into inositol phospholipids in the platelets. All three lipids were labeled in unstimulated platelets, but incorporation of 32P changed rapidly by 15 s after thrombin stimulation, suggesting that they are important in platelet activation. Specific inositol polyphosphate phosphatases were used to both identify the lipid structures and to determine the route of synthesis of these lipids. During 32P labeling and after thrombin stimulation of human platelets, as much as 60% of the total radioactivity present in PtdIns(3,4)P2 was found in the D-4 phosphate and only 35% in the D-3 phosphate indicating that PtdIns(3)P is the precursor of PtdIns(3,4)P2. In addition, the D-5 and D-4 phosphates of PtdIns(3,4,5)P3 each contained 35-40% of the total radioactivity in the molecule compared with only 18-28% in the D-3 position, suggesting that PtdIns(3,4)P2 and not PtdIns(4,5)P2 is the major precursor of this lipid. These results define the predominant pathway for synthesis of these lipids in platelets as PtdIns----PtdIns(3)P----PtdIns(3,4)P2----PtdIns(3,4,5)P3.