Localization of receptor-human chorionic gonadotropin complex to the surface of the luteal and interstitial glandular cells in the pseudopregnant rat ovaries with the peroxidase-antiperoxidase (PAP) complex method

Receptor-bound hCG was localized in pseudopregnant rat ovarian cells at semiultrastructural level with the peroxidase-antiperoxidase (PAP) complex method. The animals received 2, 6, 12 or 24 h prior to killing a single intravenous injection of hCG and the hormone was localized in the 5-micrometer paraffin sections and in the 1-micrometer epon sections using the pre-embedding technique. The peroxidase staining localized to the periphery of the luteal and interstitial glandular cells. No significant staining occurred in the intracellular structures of the cells during the 24-h observation period. However, the appearance of staining in the subplasmalemmal structures can not be excluded. These results are compatible with the previous observations that the receptor-hCG complexes are primarily formed at the surface of the luteal and interstitial glandular cells.     

Purification and characterization of the assembly factor P17 of the lipid-containing bacteriophage PRD1.

Assembly factors, proteins assisting the formation of viral structures, have been found in many viral systems. The gene encoding the assembly factor P17 of bacteriophage PRD1 has been cloned and expressed in Escherichia coli. P17 acts late in phage assembly, after capsid protein folding and multimerization, and sorting of membrane proteins has occurred. P17 has been purified to near homogeneity. It is a tetrameric protein displaying a rather high heat stability. The protein is largely in an alpha-helical conformation and possesses a putative leucine zipper which is not essential for protein function, as judged by in vitro mutagenesis and complementation analysis. Although heating does not cause structural changes in the conformation of the protein, the dissociation of the tetramer into smaller units is evident as diminished self-quenching of the fluorescently labeled P17. Similarly, dissociation of the tetramer is also obtained by dialysis of the protein against 6-M guanidine hydrochloride (GdnHCl) or 1% SDS. The reassembly of these smaller units upon cooling is evident from resonance energy transfer.     

Solubilization of proteins in dimethyl sulfoxide by permethylation: application to structural studies of apolipoprotein B

The delipidated protein moiety, apolipoprotein B, of human low-density lipoproteins was permethylated in potassium butoxide/dimethyl sulfoxide with methyl iodide. The derivatized protein was soluble in dimethyl sulfoxide and, in the presence of sodium dodecyl sulfate, in an aqueous buffer. Analysis of the methylated apolipoprotein B by polyacrylamide gradient gel electrophoresis in the presence of sodium dodecyl sulfate revealed five discrete bands of lower molecular mass than that of the parent 265-kDa protein, which disappeared upon permethylation. The electrophoretic behavior of the methylated apolipoprotein B was distinctly different from that of the other methylated proteins studied, including transferrin, bovine serum albumin, aldolase, beta-lactoglobulin, and apolipoprotein A-I, all of which had a higher apparent molecular weight after permethylation as compared to the corresponding native polypeptide. Calculated on the basis of methylated standard proteins the five polypeptides of apolipoprotein B have apparent molecular masses of 9.0, 16.6, 25.6, 35.7, and 46.7 kDa. The results suggest that the protein moiety of human low-density lipoprotein consists of subunits. In general, the results indicate that the permethylation method can be used to solubilize hydrophobic proteins in organic solvents for structural studies.     

Hybrid aspens responses to alkalisation of soil: growth, leaf structure, photosynthetic rate and carbohydrates

Interactions between photosynthetic rate, transpiration, content of soluble carbohydrates, leaf dimensions and structural parameters and growth of hybrid aspen (Populus tremula?×?P. tremuloides Michx.) were studied in relation to soil pH and chemical composition. The investigations were conducted in two plantations on former agricultural lands in North Estonia. One plantation was established on a territory influenced for a long time by alkaline cement dust pollution before plantation establishment and the other on an unpolluted territory. At pH 7.4 and higher concentrations of Ca, K, Mg, N and P in soil on the polluted area inhibition of height growth and diameter at breast height, leaf area and dry mass was observed compared to the unpolluted plantation with an optimum soil pH of 6.7. Differences in hybrid aspen leaves in the two plantations were related to the lower net photosynthetic and transpiration rates and higher starch and sucrose contents in the polluted plantation. Leaves from alkaline soil had a thicker palisade mesophyll layer and lower number of stomata at abaxial epidermis. The relatively low N concentration in leaves in the polluted area was associated with the low height and diameter at breast height of trees.     

The active site and the phospholipid activation of rat liver lysosomal lipase are not stereospecific

The stereochemical specificity of lysosomal lipase of rat liver was investigated using enantiomeric triacylglycerol analogs, sn-1-alkyl-2,3-diacylglycerol and sn-3-alkyl-1,2-diacylglycerol as substrates. Lysosomal lipase utilized both substrates with equal rates. The dependence of the activity of lysosomal lipase on the stereoconfiguration of activating acidic phospholipid was also studied. Our results showed that both sn-3-phospholipids (diphosphatidylglycerol, phosphatidylserine) and sn-1-phospholipids (bis(monoacylglycero)phosphate (BMP) were efficient activators of this enzyme and thus the stereochemical configuration of the activating phospholipid is not important. Accordingly, the rat liver lysosomal lipase lacks stereospecificity with respect to both the triacylglycerol substrate and the acidic phospholipid activator.