Membrane-protein interaction and the molten globule state: Interaction of α-lactalbumin with membranes

The insertion of soluble proteins into membranes has been a topic of considerable interest. We have studied the insertion of bovineα-lactalbumin into single-bilayer vesicles prepared from egg phosphatidylcholine (PC). Fluoresence studies indicated rapid and tight binding of apo-α-lactalbumin (apo-α-LA) to PC vesicles as a function of pH. The binding was maximal at pH values which favor the formation of the molten globule state. As an increase of hydrophobic surface is observed in the molten globule state, this conformational state can provide a molecular basis for insertion of soluble proteins into membranes. The membrane-bound complex formed at low pH (3.0) could be isolated and was found to be stable at neutral pH. The structural characterization of the apo-α-LA-PC complex was studied by fluorescence quenching using iodide, acrylamide, and 9,10-dibromostearic acid. The results obtained indicated that some of the tryptophans of apo-α-LA were buried in the membrane interior and some were exposed on the outer side. Fluorescence quenching and CD studies indicated the membrane-bound conformation of apo-α-LA was some conformational state that is between the soluble, fully folded conformation and the molten globule state.     

Some kinetic aspects and modelling of biotransformation of D-glucose to keto-D-gluconates

The bacterial oxidation of D-glucose to D-gluconic and keto-D-gluconic acids has been studied. Different approaches to pH-control have been checked. It is demonstrated, that the microbial growth is independent on pH-control. However, the rate of keto-gluconate production is too sensitive to the strategy of pH-maintenance and particularly to the neutralizing agent. The general opinion for the essential importance of addition of calcium ions for keto-gluconate formation is confirmed. The interpretation of the obtained experimental data by means of a simple mathematical model shows that the apparent lag-phase in keto-gluconate production is probably due to the necessity of accumulation of biomass as a biocatalyst and gluconic acids as a substrate.     

A recognition component of the ubiquitin system is required for peptide transport in Saccharomyces cerevisiae

Peptide transport in Saccharomyces cerevisiae is controlled by three genes: PTR1, PTR2, and PTR3. PTR1 was cloned and sequenced and found to be identical to UBR1, a gene previously described as encoding the recognition component of the N-end-rule pathway of the ubiquitin-dependent proteolytic system. Independently derived ubr1 mutants, like ptr1 mutants, were unable to transport small peptides into ceils. Concomitantly, ptr1 mutants, like ubr1 mutants, were unable to degrade an engineered substrate of the N-end-rule pathway. Further, ptr1 mutants did not express PTR2, a gene encoding the integral membrane component required for peptide transport in S. cerevisiae. These results establish a physiological role for a protein previously known to be required for the degradation of N-end-rule substrates. Our findings show that peptide transport and the ubiquitin pathway—two dynamic phenomena universal to eukaryotic cells—share a common component, namely UBR1/PTR1.     

Chromosomal Localization, Embryonic Expression, and Imprinting Tests for Bmp7 on Distal Mouse Chromosome 2

Murine Bmp7 has been assigned to distal Chromosome 2 by interspecific backcross mapping. The map location suggests close linkage to classical mouse mutations and places Bmp7 within a chromosome region thought to contain one or more unidentified imprinted genes. A direct test suggests that Bmp7 is not imprinted. An examination of embryonic RNA expression patterns shows that Bmp7 is expressed in a variety of skeletal and nonskeletal tissues. Both embryonic expression patterns and the human chromosomal sublocalization inferred from its mouse location make Bmp7 a candidate for the gene affected in some patients with Holt-Oram syndrome.     

Methods Involving Light Variation for Isolation of Cyanobacteria: Characterization of Isolates from Central Australia

We report the isolation of organisms belonging to a range of cyanobacterial genera from the remote arid region of central Australia, together with a preliminary characterization of their temporal modes of nitrogen fixation. We rendered unialgal Dermocarpa and Myxosarcina spp. (Section II organisms), LPP group B: type X (Section III), and Scytonema and Nostoc spp. (Section IV). We developed an isolation procedure based on a combination of published methods and applicable to a broad spectrum of cyanobacterial genera. We found light intensity to be a critical variable in our methodology; it was also an important determinant of the proportions of different organisms growing in stable mixtures.     

X-ray microanalytical detection of iron in pigmentation of oral mucosa.

A patient was referred to the Charles Clifford Dental Hospital with a grey metallic pigmentation of the hard palate. Conventional histopathological examination was inconclusive, suggesting the presence of either an ephelis (freckle) of pigmentation resulting from a stainless steel upper denture. Material from the pathological specimen was dewaxed and reembedded in Spurr's resin. Examination in the TEM revealed electron dense deposits in the cytoplasm of macrophages. Energy dispersive X-ray microanalysis demonstrated that these inclusions contained iron. The results suggested that the iron was in a form similar to haemosiderin and had arisen from the steel denture.