Metabolic transformations of some ent-kaurenes in Gibberella fujikuroi

The conversion of ent-kaur-16-enes to gibberellic acid in Gibberella fujikuroi is blocked by A-ring modifications. Thus ent-3β-hydroxykaur-16-en-19-yl succinate gives good conversion (46%) to the 7β-hydroxy derivative.* Under the same conditions the 3β-epimer gives 7β- or 6α-hydroxylation and the former occurs for the 3-oxo analogue. The succinoyloxy function acts as a less efficient block and ent-kaur-16-en-19-yl succinate is converted to 7β-hydroxy and 6β,7β-dihydroxy derivatives along with gibberellic acid. Hydrolysis of the succinate block of the metabolities provides the 7β, 19-diol and 6β,7β, 19-triol. Of this pair only the former was effectively metabolized to gibberellic acid in G. fujikuroi.     

Cyclophilin 40: An Hsp90-cochaperone associated with apo-steroid receptors

Cyclophilin 40, a divergent loop cyclophilin first identified in association with the estrogen receptor α, contains a C-terminal tetratricopeptide repeat domain through which it shares structural identity with FK506-binding protein 52 (FKBP52) and other partner cochaperones in steroid receptor-heat shock protein 90 (Hsp90) complexes. By dynamically competing for Hsp90 interaction, the cochaperones allow the receptors to establish distinct Hsp90-chaperone complexes, with the potential to exert tissue-specific control over receptor activity. Cyclophilin 40 regulates Hsp90 ATPase activity during receptor-Hsp90 assembly. Functional deletion of the cyclophilin 40 yeast homologue, Cpr7, adversely affected estrogen receptor α and glucocorticoid receptor activity that could be fully restored, either with wild type Cpr7 or Cpr7 with a cyclophilin domain lacking isomerase activity. We draw parallels with the mechanism already established for FKBP52 and propose that the cyclophilin 40 divergent loop interfaces with a contact surface on the steroid receptor ligand-binding domain to achieve an optimal orientation for receptor activity.     

Glutamate dehydrogenase isoforms in lupine roots and root nodules. Immunological studies

In roots of the lupine ( Lupinus luteus L. cv. Ventus) glutamate dehydrogenase (EC 1.4.1.2–4) was present in a single, electrophoretically homogeneous form (GDH_R), while in root nodules eight forms of the enzyme (GDH_N) were detected. Highly purified fractions of glutamate dehydrogenase from roots and nodules were used to prepare antisera in rabbits. The two antisera recognized extracts of glutamate dehydrogenase from both roots and nodules. Low concentrations of the antiserum raised against nodule glutamate dehydrogenase precipitated GDH from the nodule extract (the homologous antigen) effectively but decreased the activity of GDH from the root extract only slightly. At high concentrations, however, the antiserum totally precipitated both enzyme extracts. Ouchterlony's double diffusion test showed that seven forms of root nodule glutamate dehydrogenase arose as the result of random association of two subunits in a hexameric complex, while the eighth form probably consisted of totally distinct subunits. The question of whether the new glutamate dehydrogenase forms, present exclusively in root nodules, can be classified as nodulins, is discussed.     

Immunochemical comparison of the glutamate dehydrogenase isoenzymes in yellow lupin root nodules

Monospecific antisera against three glutamate dehydrogenase (GDH) subunits of lupin root nodules were obtained. The use of sensitive mixed rocket immunoelectrophoresis enabled detection of seven GDH forms at the early stage of nodule development, thus providing evidence for the earlier hypothesized (L. Ratajczak et al., 1986, Physiol. Plant., 67, 685-689) random association of subunits 2g and 2a to form the remaining five GDH forms. All seven forms were localized in mitochondria. Immunological similarity was found between form 1 and plastid GDH.     

Intra-systemic inhibitors of the hematopoietic system]

Physiological, experimental and theoretical aspects concerning haemopoietic inhibitors are reviewed. In the paper there are also discussed future research directions of this branch of haematology.     

Purification of the molybdate-stabilized 9-10 S estradiol receptor from calf uterus

The molybdate-stabilized calf uterine estradiol receptor has been purified to near-homogeneity by a three-step procedure. Initial purification by heparin-Sepharose chromatography provides a concentrated receptor extract in 40% yield with a 5-10-fold increase in purity. The inclusion of molybdate in phosphate-buffered cytosol enhances 9-10 S receptor stability in high salt and allows elution of the oligomeric receptor complex from heparin-Sepharose with 0.4 M KCl. A second affinity step utilizing estrone carboxymethyloxime coupled to diaminoethyl bis(2-hydroxypropoxy)butane-Sepharose Cl-4B increases purification by a further 1600-fold. High performance liquid chromatography gives homogeneous receptor which migrates on sodium dodecyl sulfate-polyacrylamide gel electrophoresis as a polypeptide of Mr approximately 89,000. The purified molybdate-stabilized receptor sediments at 9.3 +/- 0.2 S (n = 4) in glycerol gradients and has a Stokes radius of 74 +/- 3 A (n = 2) giving a calculated Mr approximately 290,000. These properties and the steroid-binding specificity of the purified receptor bear a close similarity to those found for the 9-10 S receptor in crude cytosol.     

IbpA the small heat shock protein from Escherichia coli forms fibrils in the absence of its cochaperone IbpB

Small heat shock proteins (sHsps) associate with aggregated proteins, changing their physical properties in such a way that chaperone mediated disaggregation becomes much more efficient. In Escherichia coli two small Hsps, IbpA and IbpB, exist. They are 48% identical at the amino acid level, yet their roles in stabilisation of protein aggregates are quite distinct. Here we analysed the biochemical properties of IbpA. We found that IbpA assembles into protofilaments which in turn form mature fibrils. Such fibrils are atypical for sHsps. Interaction of IbpA with either its cochaperone IbpB or an aggregated substrate blocks IbpA fibril formation.

Structured summary

MINT-7876715: ibpA (uniprotkb:P0C054) and ibpA (uniprotkb:P0C054) bind (MI:0407) by molecular sieving (MI:0071)MINT-7888427: ibpB (uniprotkb:P0C058) and ibpB (uniprotkb:P0C058) bind (MI:0407) by molecular sieving (MI:0071)MINT-7888448: ibpA (uniprotkb:P0C054) and ibpA (uniprotkb:P0C054) bind (MI:0407) by electron microscopy (MI:0040)MINT-7888434: ibpB (uniprotkb:P0C058) and ibpB (uniprotkb:P0C058) bind (MI:0407) by electron microscopy (MI:0040)MINT-7888459: ibpA (uniprotkb:P0C054) and ibpA (uniprotkb:P0C054) bind (MI:0407) by fluorescence microscopy (MI:0416)