Identification of a novel acidic mammalian chitinase distinct from chitotriosidase

Chitinases are ubiquitous chitin-fragmenting hydrolases. Recently we discovered the first human chitinase, named chitotriosidase, that is specifically expressed by phagocytes. We here report the identification, purification, and subsequent cloning of a second mammalian chitinase. This enzyme is characterized by an acidic isoelectric point and therefore named acidic mammalian chitinase (AMCase). In rodents and man the enzyme is relatively abundant in the gastrointestinal tract and is found to a lesser extent in the lung. Like chitotriosidase, AMCase is synthesized as a 50-kDa protein containing a 39-kDa N-terminal catalytic domain, a hinge region, and a C-terminal chitin-binding domain. In contrast to chitotriosidase, the enzyme is extremely acid stable and shows a distinct second pH optimum around pH 2. AMCase is capable of cleaving artificial chitin-like substrates as well as crab shell chitin and chitin as present in the fungal cell wall. Our study has revealed the existence of a chitinolytic enzyme in the gastrointestinal tract and lung that may play a role in digestion and/or defense.     

Expression, secretion and antigenic variation of bacterial S-layer proteins

The function of the S-layer, a regularly arranged structure on the outside of numerous bacteria, appears to be different for bacteria living in different environments. Almost no similarity exists between the primary sequences of S-proteins, although their amino acid composition is comparable. S-protein production is directed by single or multiple promoters in front of the S-protein gene, yielding stable mRNAs. Most bacteria secrete S-proteins via the general secretory pathway (GSP). Translocation of S-protein across the outer membrane of Gram-negative bacteria sometimes occurs by S-protein-specific branches of the GSP. O-polysaccharide side-chains of the lipopolysaccharide component of the cell wall of Gram-negative bacteria appear to function as receptors for attachment of the S-layer. Silent S-protein genes have been found in Campylobacter fetus and Lactobacillus acidophilus. These silent genes are placed in the expression site in a fraction of the bacterial population via inversion of a chromosomal segment.     

Organic geochemical changes in Pliocene sediments of ODP Site 1083 (Benguela Upwelling System)

The intensification of the Northern Hemisphere Glaciation (INHG) was a major event in the development of the current climate state, and as one of the most productive regions in the world's oceans, the behaviour of the Benguela Upwelling System (BUS) following the INHG is of wide interest. To investigate post-INHG changes in productivity and organic matter accumulation, total organic carbon and biomarker accumulation rates were determined for sediments from ODP Site 1083 and compared to alkenone-derived sea surface temperatures and nitrogen isotopic compositions. These data indicate that the interval between 2.6 and 2.4 Ma was characterized by dramatic changes in upwelling intensity and organic carbon export on the northern edge of the modern BUS. The upwelling is reflected by significant changes in alkenone-derived SST estimates between glacial and interglacial intervals, with a total variability of 16 °C. The studied interval is also characterized by large changes in organic matter export as reflected by changes in TOC and biomarker accumulation rates, which show maxima during OIS 98 and during the transition from OIS 97 to 96. Intervals of elevated TOC are also characterized by elevated concentrations of sedimentary microbial biomarkers and lower %CaCO₃, suggesting that enhanced delivery of labile organic matter to the seafloor resulted in enhanced remineralisation with released CO₂ being consumed by CaCO₃ dissolution. However, in apparent contrast to recent Pleistocene sediments at the same site, organic matter export after the INHG was not solely driven by upwelling intensity. Of the three Pliocene glacial–interglacial cycles examined (OIS 101 to 96), each is unique with respect to the timing and magnitude of changes in organic matter accumulation. Each is also characterized by different algal assemblages as inferred from biomarker distributions, with OIS 97 and 96 particularly dominated by diatoms. We suggest that these differences reflect the important but evolving role of Southern Ocean waters in the Pliocene BUS: nutrient depletion of SO waters occurred during parts of Pliocene glacial intervals such that even intense upwelling did not persistently result in enhanced organic matter accumulation rates.     

N-ras mutations in human cutaneous melanoma from sun-exposed body sites.

In 7 of 37 patients with cutaneous melanoma, mutations in the N-ras gene were found. The primary tumors of these seven patients were exclusively localized on body sites continuously exposed to sunlight. Moreover, the ras mutations were all at or near dipyrimidine sites known to be targets of UV damage. Two primary tumors were biclonal with respect to ras mutation. An active role for UV irradiation in induction of the mutations is suggested.     

The New Face of Debt-Peonage in the Bolivian Amazon: Social Networks and Bargaining Instruments

The debt-peonage system is an agreement between patrons and laborers in different economic activities worldwide. A common feature is social exploitation of laborers that generate profits to the patrons. In recent literature it has been argued that debt-peonage can be an economically sound arrangement that secures the needs of actors. The paper evaluates to what extent traditionally strong debt-peonage in forest-dwelling communities in the Bolivian Amazon, has developed in a way that better secures the needs and economic interest of multiple actors. Case studies in sixteen communities yielded qualitative information on debt relations between peasants, traders and former patrons. Debt-peonage changed from a mechanism to provide and keep workforce indebted to new social relationships, equitable commercial links, opportunity to access work capital and production chain diversification. This rapid shift was caused by important changes in land and forest regulations.