Histologic assessment of nerve regeneration in the rat

This study reports the degree of spontaneous regeneration that will occur in the sciatic nerve of a rat 5 months after complete resection of the nerve. In 30 animals, the sciatic nerve was excised. Histological assessment at 5 months revealed evidence of regeneration for a variable distance (mean 23.7 mm +/- 6.4 mm). Histological sections were studied at 1-cm intervals along the length of the nerve. Evidence of compartmentation with "minifascicle" formation was noted. The orientation of the nerve fibers was parallel to the long axis of the nerve. This study assessing spontaneous regeneration is meant to serve as a control for other studies evaluating the effect of factors that may influence nerve regeneration in the rat model.     

Which component of sulphasalazine is active in rheumatoid arthritis?

Sulphasalazine is known to be effective as a second line agent in the treatment of rheumatoid arthritis. The two chemical constituents of sulphasalazine (sulphapyridine and 5-aminosalicylic acid) were assessed separately in the treatment of rheumatoid arthritis. Over 24 weeks sulphapyridine showed a pronounced second line effect comparable with sulphasalazine and with a similar toxicity profile, whereas 5-aminosalicylic acid showed only a weak first line effect. Thus sulphapyridine appears to be the active moiety responsible for the second line effect of sulphasalazine in rheumatoid arthritis. The efficacy of the antibacterial component of sulphasalazine yet again permits speculation about the role of a bacterial pathogen in the aetiopathogenesis of rheumatoid disease.     

C-kinase phosphorylates the epidermal growth factor receptor and reduces its epidermal growth factor-stimulated tyrosine protein kinase activity

The Ca2+- and phospholipid-dependent protein kinase (C-kinase) binds tightly in the presence of Ca2+ to purified membranes of A431 human epidermoid carcinoma cells. The major membrane substrate for C-kinase is the epidermal growth factor (EGF) receptor. Phosphorylation of the EGF receptor is Ca2+-dependent and occurs at threonine and serine residues. After tryptic digestion of the receptor, three major phosphothreonine-containing peptides were identified. These are identical with three new phosphopeptides present in the EGF receptor isolated from A431 cells treated with either of the tumor promoters 12-O-tetradecanoylphorbol 13-acetate or teleocidin. C-kinase catalyzes phosphorylation at these same sites in purified EGF receptor protein. These results indicate that, in A431 cells exposed to tumor promoters, C-kinase catalyzes phosphorylation of a significant population of EGF receptor molecules. This phosphorylation of EGF receptors results in decreased self-phosphorylation of the EGF receptor at tyrosine residues both in vivo and in vitro and in decreased EGF-stimulated tyrosine kinase activity in vivo.     

The protein-tyrosine kinase substrate p36 is also a substrate for protein kinase C in vitro and in vivo.

p36, a major in vivo substrate of protein-tyrosine kinases, is shown to be phosphorylated at serine 25, a site very close to the major site of tyrosine phosphorylation by pp60v-src, tyrosine 23 (J. R. Glenney, Jr., and B. F. Tack, Proc. Natl. Acad. Sci. USA 82:7884-7888, 1985). We present evidence suggesting that protein kinase C mediates phosphorylation of serine 25.     

Structural characterisation of the bromouracil.guanine base pair mismatch in a Z-DNA fragment.

The deoxyoligonucleotide d(BrU-G-C-G-C-G) was crystallised at pH 8.2 and its structure analysed by X-ray diffraction. The unit cell, of dimensions a = 17.94, b = 30.85, c = 49.94A contains four DNA duplexes in space group P2(1)2(1)2(1). The duplexes are in the Z conformation, with four Watson-Crick G.C base pairs and two BrU.G base pairs. The structure was refined to an R factor of 0.16 at a resolution of 2.2A with 64 solvent molecules located. The BrU.G base pair mismatch is of the wobble type, with both bases in the major tautomer form and hydrogen bonds linking 0-2 of BrU with N-1 of G and N3 of BrU with 0-6 of G. There is no indication of the presence of ionised base pairs, in spite of the high pH of crystallisation. The results are discussed in terms of the mutagenic properties of 5- bromouracil.     

Osteogenesis imperfecta type IV: evidence of abnormal triple helical structure of type I collagen

Summary Skin fibroblasts from a patient with mild osteogenesis imperfecta (OI) type IV synthesize two populations of type I procollagen molecules. One population contains pro1(I) and pro2(I) chains that migrate normally in sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and a second population contains only slower migrating pro1(I) and pro2(I) chains. The total amount of type I procollagen made by OI cells and the ratio of pro1(I): pro2(I) is normal. When labeled under conditions that inhibit post-translational modification of pro chains, the OI cells produce only single populations of pro1(I) and pro2(I) chains indicating that the apparent increased molecular weight of some OI pro chains is due to excessive post-translational modification rather than peptidyl insertions. Peptide maps indicate that excessive post-translational modification occurs along the entire triple helical segment of some 1(I) and 2(I) chains produced by OI cells. The effect of the mutation is to lower the melting temperature of the molecules containing slow migrating 1(I) and 2(I) chains to 39.5°C (compared to 41.5°C for control), and to delay secretion of the overmodified type I procollagen from OI cells. These data are consistent with a mutation near the carboxyl-terminal end of the triple helical domain which delays triple helical formation and renders all chains available for further post-translational modification amino-terminal to the mutation. Such alterations in triple helical structure, thermal stability, and secretion previously associated only with the lethal OI type II phenotype are thus also seen in the mild OI type IV phenotype.     

Structural features and hydration of d(C-G-C-G-A-A-T-T-A-G-C-G); a double helix containing two G.A mispairs

Single crystal X-ray diffraction techniques have been used to characterise the molecular structure of the title compound to 2.5A resolution. The structure consists of ten standard Watson-Crick base pairs and two G.A mismatched base pairs. The purine-purine mismatches have guanine in the usual anti orientation with respect to the sugar and adenine in syn orientation. There are two hydrogen bonds formed between the mismatch bases, N-1 and O-6 of guanine with N-7 and N-6 of adenine respectively. The bulky purine-purine mismatches are accommodated with minor perturbation of the sugar-phosphate backbone. There is a slight improvement in base pair overlap at the mismatch sites. Details of the backbone conformation, base stacking interactions and hydration are presented and compared with those of the parent compound d(C-G-C-G-A-A-T-T-C-G-C-G).     

Epidermal growth factor receptor metabolism and protein kinase activity in human A431 cells infected with Snyder-Theilen feline sarcoma virus or harvey or Kirsten murine sarcoma virus.

When human A431 cells, which carry high numbers of epidermal growth factor (EGF) receptors, are exposed to EGF, the total content of phosphotyrosine in cell protein is increased, the EGF receptor becomes phosphorylated at tyrosine, and new phosphotyrosine-containing 36,000- and 81,000-dalton proteins are detected. We examined the properties of A431 cells infected with Snyder-Theilen feline sarcoma virus, whose transforming protein has associated tyrosine protein kinase activity, and Harvey and Kirsten sarcoma viruses, whose transforming proteins do not. In all cases, the infected cells were more rounded and more capable of anchorage-independent growth than the uninfected cells. EGF receptors were assayed functionally by measuring EGF binding and structurally by metabolic labeling and immunoprecipitation. In no case did infection appear to alter the rate of EGF receptor synthesis, but infection reduced EGF receptor stability by about 50% for cloned Harvey sarcoma virus-infected cells and by 80% for cloned feline sarcoma virus-infected cells. The corresponding reductions in EGF binding were 70 and 90%, respectively. The proteins of feline sarcoma virus-infected A431 cells contained an increased amount of phosphotyrosine, and the 36,000- and 81,000-dalton phosphoproteins were detected. The EGF receptor was not detectably phosphorylated at tyrosine, however, unless the cells were exposed to EGF. The Harvey and Kirsten sarcoma virus-infected cells did not exhibit elevated levels of phosphotyrosine either in the total cell proteins or in the EGF receptor, nor were the 36,000- and 81,000-dalton proteins detectable. However, these phosphoproteins were found in the infected cells after EGF treatment. Thus, all of the infected A431 cells exhibited reduced EGF binding and increased degradation of EGF receptors, yet their patterns of protein phosphorylation were distinct from those of EGF-treated A431 cells.     

Variation in aufwuchs at six freshwater habitats in terms of carbon biomass and of carbon: Nitrogen ratio

1. From May to December 1971 at six sites in upstate New York, samples of freshwater Aufwuchs (the largely algal “scum” flora) were collected on sets of exposed microscope slides. Successive standing crop biomass estimates are presented as analyses of total organic carbon (by wet oxidation) and total nitrogen (by micro-Dumas). Nutritional quality of the Aufwuchs can be assessed in carbon to nitrogen (C:N) ratios, and these are correlated with substantive data from concurrent studies on the growth and fecundity of second trophic level snails (Laevapex and Lymnaea).
2. Peak values of carbon biomass for the six sites range from 1.1 mgC/dm² to 4.2 mgC/dm², and mean C:N ratios ranged from 3.7:1 to 10.1:1 (corresponding to 29% protein). Higher snail growth rates (computed as increase in mgC/100 snails/30 days) and greater fecundities correlate, beyond certain minimal levels of carbon biomass, to lower C:N ratios in the corresponding Aufwuchs samples.
3. In discussing these nutritional aspects of Aufwuchs production, it is emphasized that freshwater macrophytes have C:N ratios well above 17:1, and are not much fed upon. In smaller bodies of fresh water, the most important sector of primary production is that of the Aufwuchs, and its nutritional quality in terms of lower C:N ratios is of unique significance to the bioenergetics of the second trophic level invertebrates.