Low-energy constraints on supergravity parameters

We make a careful analysis of the constraints on supergravity parameters from the requirement of SU(2)×U(1) symmetry breaking. Since we obtain fully analytic solutions to the relevant renormalization group equations, we are able to explore the whole range of parameters. Breaking electroweak symmetry with a light top quark leads to a strong correlation between the dimensionless parameters and the mass ratios in the supergravity lagrangian. However, the overall mass scale, e.g. $\text{m}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$, is not fixed by this requirements. The bound on the lightest neutral Higgs boson is reexamined. The lightest squark is usually an s-top, but we easily find cases where it is a s-bottom. Unfortunately the low-energy constraints provide no useful guidelines for experimentalists.     

Algebraic study of chiral anomalies?

The algebraic structure of chiral anomalies ismade globally valid on non-trivial bundles by the introduction of a fixed background connection. Some of the techniques used in the study of the anomaly are improved or generalized, including a systematic way of generating towers of ??descent equations??.     

Equal-sign dileptons and heavy-quark detection

The production of the t-quark should be associated with a large rate of equal-sign lepton pairs. We estimate the (single and double) angular distributions of events weighted by powers of the leptonic energies, in e⁺e^? → ?⁺?⁺ (?^??^?) … . These quantities provide interesting information on heavy-quark decay and fragmentation in a transparent way.     

A new unified theory with right-handed currents and proton stability

A unified vector-like gauge theory based on SU(6) is proposed, where the proton stability is achieved with reasonable lepto-quark massemeasurable in the decay K_L⁰→μe. We predict the existence of a long-lived messon decaying into Pe^?.     

Spontaneous symmetry breaking in O(10)

We consider the most general renormalizable O(10) invariant potential for a $\text{45 + 16 +}\text{16}$ representation of Higgs fields. We show that O(10) can be spontaneously broken down to SU(5), SU(4) × U(1) or SU(3) × SU(2) × U(1), this last case being, of course, the most appealing.     

Can inflation induce supersymmetry breaking in a metastable vacuum?

We argue that fields responsible for inflation and supersymmetry breaking are connected by gravitational couplings. In view of the recent progress in studying supersymmetry breaking in a metastable vacuum, we have shown that in models of supersymmetric hybrid inflation, where R-symmetry plays an important role, the scale of supersymmetry breaking is generated dynamically at the end of inflation and turns out to be consistent with gravity mediation.     

The <Emphasis Type="Italic">Mycobacterium tuberculosis</Emphasis> Rv2540c DNA sequence encodes a bifunctional chorismate synthase

Background

The emergence of multi- and extensively-drug resistant Mycobacterium tuberculosis strains has created an urgent need for new agents to treat tuberculosis (TB). The enzymes of shikimate pathway are attractive targets to the development of antitubercular agents because it is essential for M. tuberculosis and is absent from humans. Chorismate synthase (CS) is the seventh enzyme of this route and catalyzes the NADH- and FMN-dependent synthesis of chorismate, a precursor of aromatic amino acids, naphthoquinones, menaquinones, and mycobactins. Although the M. tuberculosis Rv2540c (aroF) sequence has been annotated to encode a chorismate synthase, there has been no report on its correct assignment and functional characterization of its protein product.

Results

In the present work, we describe DNA amplification of aroF-encoded CS from M. tuberculosis (Mt CS), molecular cloning, protein expression, and purification to homogeneity. N-terminal amino acid sequencing, mass spectrometry and gel filtration chromatography were employed to determine identity, subunit molecular weight and oligomeric state in solution of homogeneous recombinant Mt CS. The bifunctionality of Mt CS was determined by measurements of both chorismate synthase and NADH:FMN oxidoreductase activities. The flavin reductase activity was characterized, showing the existence of a complex between FMN_ox and Mt CS. FMN_ox and NADH equilibrium binding was measured. Primary deuterium, solvent and multiple kinetic isotope effects are described and suggest distinct steps for hydride and proton transfers, with the former being more rate-limiting.

Conclusion

This is the first report showing that a bacterial CS is bifunctional. Primary deuterium kinetic isotope effects show that C₄-proS hydrogen is being transferred during the reduction of FMN_ox by NADH and that hydride transfer contributes significantly to the rate-limiting step of FMN reduction reaction. Solvent kinetic isotope effects and proton inventory results indicate that proton transfer from solvent partially limits the rate of FMN reduction and that a single proton transfer gives rise to the observed solvent isotope effect. Multiple isotope effects suggest a stepwise mechanism for the reduction of FMN_ox. The results on enzyme kinetics described here provide evidence for the mode of action of Mt CS and should thus pave the way for the rational design of antitubercular agents.