Differences in glycerolipid synthesis and insulin regulation in rat hepatocytes and adipocytes

Glycerolipid synthesis was studied by determining radioactive incorporation from either [1-14C] acetate or [U-14C] palmitate. Glycerolipid synthesis in adipocytes, mainly from exogenous palmitate, was preferentially directed to the formation of triacylglycerols, whereas in hepatocytes triacylglycerols and phospholipids were synthesized at similar rates. Insulin stimulated glycerolipid synthesis from acetate in both types of cells, being triacylglycerols more significantly increased than phospholipids. The most relevant difference was the finding that in adipocytes insulin strongly stimulated the formation of diglycerides, apparently from phosphatidate, whereas in hepatocytes insulin only slightly increased diglyceride levels. A possible role of diacylglycerol in insulin action in adipocytes, but not in hepatocytes, is also discussed.     

Penetration of Bdellovibrio bacteriovorus into Host Cells

Electron microscopy reveals that, in Bdellovibrio infection, after the formation of a passage pore in the host cell wall, the differentiated parasite penetration pole is associated with the host protoplast. This firm contact persists throughout the parasite penetration and after this process is completed. In penetrated hosts this contact is also apparent by phase microscopy. The association between the walls of the parasite and the host at the passage pore, on the other hand, is transient. Bdellovibrio do not penetrate hosts whose protoplast and cell walls are separated by plasmolysis, or in which the membrane-wall relationship is affected by low turgor pressure. It is concluded, therefore, that for penetration to occur it is essential that the host protoplast be within reach of the parasite, so that a firm contact can be established between them. A penetration mechanism is proposed that is effected by forces generated by fluxes of water and solutes due to structural changes in the infected host envelope. These forces cause a differential expansion of the host protoplast and cell wall and their separation from each other around the entry site, while the parasite remains firmly anchored to the host protoplast. Consequently, the parasite ends up enclosed in the expanded host periplasm. The actual entry, therefore, is a passive act of the parasite.     

Location,structure and behaviour of C-heterochromatin during meiosis in Dichroplus silveiraguidoi (Acrididae-Orthoptera)

The constitutive heterochromatin of Dichroplus silveiraguidoi, a species which shows an exceptionally low chromosome number (2n=8), was studied at meiosis with a staining technique on normal and hypotonically treated specimens. The results showed: 1) an unusual behaviour of the heterochromatic blocks located in the so-called synaptic region of the sex bivalent (Neo Y-Neo X), which remains paired from early prophase through metaphase I; 2) in normal or in hypotonically treated cells a heterogeneous configuration of the C-heterochromatic blocks was observed. This configuration is characterized by the existence of small positive granules interconnected by euchromatic filaments and is enhanced by treatment with a low ionic strength solution; 3) A weakly positive stained (intermediate) material was demonstrated in the Neo X chromosome; 4) A large amount of heterochromatin is distributed in the form of granular material along the length of the autosomes and as telomeric and centromeric blocks in all chromosomes. The possible evolutionary mechanisms involved and the significance of the C-band heterochromatin demonstrated in this species are discussed.     

Population genetics in the American tropics. II. The comparative genetics ofDrosophila in european and neo-tropical environments

We have attempted to make quantitative comparisons between the genetic systems provoked by some neo-tropical environments and a European one. These comparisons permit certain clarifications regarding the comprehension of the genetic load and of the genetic norm in reference to particular ecological characteristics.     

Significance of Signs and Symptoms in Benign Prostatic Hypertrophy

Measurements of intravesical pressure, urinary flow rate, retrograde cystographic residual urine, reflux of contrast medium into the prostatic ducts, and radiological prostate size were made in 45 men with benign prostatic hypertrophy. These factors were all found to be good clinical indices of the degree of urethral resistance to micturition; on the other hand, there was no relation between the latter and the severity of symptoms.     

Use of restrained molecular dynamics in water to determine three-dimensional protein structure: prediction of the three-dimensional structure of Ecballium elaterium trypsin inhibitor II

Refinement of distance geometry (DG) structures of EETI-II (Heitz et al.: Biochemistry 28:2392-2398, 1989), a member of the squash family trypsin inhibitor, have been carried out by restrained molecular dynamics (RMD) in water. The resulting models show better side chain apolar/polar surface ratio and estimated solvation free energy than structures refined "in vacuo." The consistent lower values of residual NMR constraint violations, apolar/polar surface ratio, and solvation free energy for one of these refined structures allowed prediction of the 3D folding and disulfide connectivity of EETI-II. Except for the few first residues for which no NMR constraints were available, this computer model fully agreed with X-ray structures of CMTI-I (Bode et al.: FEBS Lett. 242:285-292, 1989) and EETI-II complexed with trypsin that appeared after the RMD simulation was completed. Restrained molecular dynamics in water is thus proved to be highly valuable for refinement of DG structures. Also, the successful use of apolar/polar surface ratio and of solvation free energy reinforce the analysis of Novotny et al. (Proteins 4:19-30, 1988) and shows that these criteria are useful indicators of correct versus misfolded models.