Interconnected assembly factors regulate the biogenesis of mitoribosomal large subunit

Mitoribosomes consist of ribosomal RNA and protein components, coordinated assembly of which is critical for function. We used mitoribosomes from Trypanosoma brucei with reduced RNA and increased protein mass to provide insights into the biogenesis of the mitoribosomal large subunit. Structural characterization of a stable assembly intermediate revealed 22 assembly factors, some of which have orthologues/counterparts/homologues in mammalian genomes. These assembly factors form a protein network that spans a distance of 180 Å, shielding the ribosomal RNA surface. The central protuberance and L7/L12 stalk are not assembled entirely and require removal of assembly factors and remodeling of the mitoribosomal proteins to become functional. The conserved proteins GTPBP7 and mt‐EngA are bound together at the subunit interface in proximity to the peptidyl transferase center. A mitochondrial acyl‐carrier protein plays a role in docking the L1 stalk, which needs to be repositioned during maturation. Additional enzymatically deactivated factors scaffold the assembly while the exit tunnel is blocked. Together, this extensive network of accessory factors stabilizes the immature sites and connects the functionally important regions of the mitoribosomal large subunit.     

Accumulation pattern of arachin and its subunits in maturation of groundnut seeds

The accumulation pattern of arachin and its subunits in growinggroundnuts was investigated. Soluble proteins were extractedfrom the kernels at twelve different stages of maturation (4–16weeks after pegging). Fractionation showed arachin, conarachinII, 5S and 2S protein components with sucrose gradient centrifugation.Ten weeks after pegging, only 35% of the maximum amount of arachinhad accumulated, whereas conarachin II was 85%, the 5S component89%, and the 2S component 76%. Arachin, however, increased rapidlyin the later stage of maturation. No change in the subunit ratioin arachin during seed growth was observed on the patterns ofsodium dodecyl sulfate-gel electrophoresis and gel isoelectricfocusing in the presence of urea. The ratio of the arachin subunitscontained in urea-extractable fraction of the kernels was constantthroughout seed development and was consistent with the subunitratio in arachin. On the other hand, the arachin subunits inthe free forms, if any, accounted for less than 1% of the associatedarachin subunits. Probably, the arachin subunits synthesizedin equimoles are associated into arachin without individualdeposition and are accumulated as arachin associates in growingseeds. (Received July 17, 1980; )     

Preliminary crystallographic study of omega-amino acid: pyruvate aminotransferase from Pseudomonas sp. F-126.

Large single crystals of ω-amino acid: pyruvate aminotransferase, were prepared by dialysis of the enzyme solution against 2.2 m-ammonium sulphate solution at pH 7.8. X-ray diffraction patterns show that the crystals belong to the orthorhombic space group I222 or I2₁2₁2₁ with unit cell dimensions $\text{a = 124.1}\text{A}\text{?}\text{, b = 137.9}\text{A}\text{?}\text{, and}\text{c = 61.2}\text{A}\text{?}$. The asymmetric unit consists of one monomer of molecular weight 43,000.     

Hypoglycemia in mice administered with fusarenon-X

Histological observation combined with determination of the serum glucose level and histochemical detection of liver glycogen was undertaken to examine the acute toxicity of fusarenon-X (FX) in mice. Mice intraperitoneally injected with a sublethal dose of the toxin showed rapidly developed hypoglycemia followed by depletion of liver glycogen. Mitotic inhibition was observed in many visceral organs and most markedly in the intestinal crypt cells, where the mitotic figures completely disappeared prior to the increase in number of the degenerated and nucrotic cells. No glycosuria was found. The disturbing effect of FX on the oral glucose tolerance test suggested the involvement of accelerated glycolysis and, more likely, of intestinal malabsorption.     

Lipofuscin and lipofuscin-like substances

Lipofuscin is defined as being a yellowish brown, lipid-rich, heterogeneous, cytoplasmic granular pigment emitting an intense yellow autofluorescence when excited with ultraviolet light, which accumulates in various tissues of animals during their aging. It is believed that the pigments are derived from the reaction of some of reactive secondary products including malonaldehyde, formed during membranous lipid peroxidation, with amino groups of phospholipids and proteins, etc., and that these formations are accompanied by alteration of the membrane structure and inactivation of the enzymes. The fluorescence measurement of the pigments is widely used as a parameter of lipid peroxidation in vivo as well as in vitro. However, their origin, chemical structure, biological significance or fate has not as yet been fully elucidated. This article introduces and discusses the recent studies on these problems.     

Crystallization and properties of myeloperoxidase from normal human leukocytes

Myeloperoxidase was purified from normal human leukocytes in a crystalline state. Two types of crystals were obtained by the batchwise and dialysis crystallization methods, one of which had a bipyramidal shape belonging to the orthorhombic system. Three multiple forms of human myeloperoxidase were separated from the crystalline enzyme by CM-Sepharose chromatography with sodium chloride gradient elution. These three multiple forms were found to have very similar enzymatic, spectroscopic, and chemical properties. However, slight differences were observed in their amino acid compositions and the molecular weights of their large subunits determined by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. Hemi-myeloperoxidase was prepared from holo-myeloperoxidase by reduction with dithiothreitol and modification with iodoacetamide, and the molecular shapes of the holo- and hemi-enzymes were determined by analytical ultracentrifugation. The axial ratios were calculated to be 2.4-3.5 for the holo-enzyme and 2.9-3.1 for the hemi-enzyme. These results suggest that the shapes of the two enzymes are more spherical in solution than the proposed structural model previously reported.