Thermoelectric Properties of NaCo<Subscript>2–<Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>

NaCo₂O₄ has one of the highest figures of merit among all ceramic thermoelectric materials. Because of its large thermopower and low resistivity, the ceramic oxide NaCo₂O₄ is a promising candidate for potential thermoelectric applications. NaCo₂O₄ is, moreover, a ceramic compound with high decomposition temperature and chemical stability in air and it does not contain any toxic elements. Like all 3-d transition ions, Co ions have multiple spin and oxidation states. In this investigation, thermopower and electrical conductivity of NaCo₂O₄ as a function of substitution of Co by Fe ions were measured. Fe substitution for Co causes resistivity to increase, whereas the Seebeck coefficient remained nearly invariant, especially above 330 K. An erratum to this article can be found at     

The alpha subunit of toluene dioxygenase from Pseudomonas putida F1 can accept electrons from reduced FerredoxinTOL but is catalytically inactive in the absence of the beta subunit

The oxygenase component of toluene dioxygenase from Pseudomonas putida F1 is an iron-sulfur protein (ISPTOL) consisting of alpha (TodC1) and beta (TodC2) subunits. Purified TodC1 gave absorbance and electron paramagnetic resonance spectra identical to those given by purified ISPTOL. TodC1 was reduced by NADH and catalytic amounts of ReductaseTOL and FerredoxinTOL. Reduced TodC1 did not oxidize toluene, and catalysis was strictly dependent on the presence of purified TodC2.     

T helper 2-dominant antilymphoma immune response is associated with fatal outcome

The precise role of the endogenous immune system in modulating cancer development remains unclear. Tumor cells are generally thought to be nonimmunogenic because they are of 'self' origin. However, tumor-reactive lymphocytes can be isolated from patients with many types of cancer. It is unclear what role these lymphocytes play and why they fail to protect the host. Using a murine B-cell leukemia/lymphoma (BCL1) model, we showed the development of a vigorous antitumor T-cell response in the tumor-susceptible host. Specific T-cell responses against BCL1 developed as early as day 4. However, the nature of this nonprotective response is different from the protective response produced in a major histocompatibility complex-matched tumor-resistant host. Susceptible hosts developed a T helper 2 (Th2)-dominant response, whereas resistant hosts developed a Th1-dominant response to BCL1. Cytolytic activity against BCL1 developed in both resistant and susceptible hosts, but in the susceptible host, this response was weaker and delayed compared with that in the resistant host. Thus, tumor susceptibility does not necessarily mean the absence of an antitumor immune response. Rather, the nature of the antitumor immune response is critical in determining clinical outcome.     

Progress in protein structure prediction

If protein structure prediction methods are to make any impact on the impending onerous task of analyzing the large numbers of unknown protein sequences generated by the ongoing genome-sequencing projects, it is vital that they make the difficult transition from computational 'gedankenexperiments' to practical software tools. This has already happened in the field of comparative modelling and is currently happening in the threading field. Unfortunately, there is little evidence of this transition happening in the field of ab initio tertiary-structure prediction.     

CATH--a hierarchic classification of protein domain structures

BACKGROUND: Protein evolution gives rise to families of structurally related proteins, within which sequence identities can be extremely low. As a result, structure-based classifications can be effective at identifying unanticipated relationships in known structures and in optimal cases function can also be assigned. The ever increasing number of known protein structures is too large to classify all proteins manually, therefore, automatic methods are needed for fast evaluation of protein structures. RESULTS: We present a semi-automatic procedure for deriving a novel hierarchical classification of protein domain structures (CATH). The four main levels of our classification are protein class (C), architecture (A), topology (T) and homologous superfamily (H). Class is the simplest level, and it essentially describes the secondary structure composition of each domain. In contrast, architecture summarises the shape revealed by the orientations of the secondary structure units, such as barrels and sandwiches. At the topology level, sequential connectivity is considered, such that members of the same architecture might have quite different topologies. When structures belonging to the same T-level have suitably high similarities combined with similar functions, the proteins are assumed to be evolutionarily related and put into the same homologous superfamily. CONCLUSIONS: Analysis of the structural families generated by CATH reveals the prominent features of protein structure space. We find that nearly a third of the homologous superfamilies (H-levels) belong to ten major T-levels, which we call superfolds, and furthermore that nearly two-thirds of these H-levels cluster into nine simple architectures. A database of well-characterised protein structure families, such as CATH, will facilitate the assignment of structure-function/evolution relationships to both known and newly determined protein structures.     

Declining sperm counts in the United States? A critical review

PURPOSE: Recent reports suggest declining sperm counts in the United States. These reports did not include all available data and did not account for geographic variations noted in prior studies. We examined all available data on U.S. sperm counts and evaluated whether geographic variations account for the decline suggested. MATERIALS AND METHODS: We reviewed all 29 U.S. studies from 1938 to 1996 reporting manually counted semen analyses of 9,612 fertile or presumably fertile men. We determined mean sperm concentrations by geographic location with weighted analysis of variance, and assessed any changes with time by linear regression analysis. RESULTS: Mean sperm concentrations from New York were significantly higher than from all other U.S. cities (98.6 versus 71.6 x 10(6) sperm per cc, respectively, p = 0.006). There has been no statistically significant change with time for mean sperm concentrations reported from New York (p = 0.49) or from U.S. cities other than New York (p = 0.62). Analysis without separating by location revealed a decline (p = 0.047). CONCLUSIONS: Sperm concentrations are highest in New York compared to other U.S. cities. When accounting for this geographic difference and examining all available data, there appears to be no significant change in sperm counts in the U.S. during the last 60 years. Further studies addressing the causes of geographic variations are needed.