Photoinactivation and photoaffinity labeling of tryptophan synthase alpha 2 beta 2 complex by the product analogue 6-azido-L-tryptophan

Nitric oxide production and sequestration in the sinus gland of the green shore crab, Carcinus maneas

Molting in decapod crustaceans is regulated by molt-inhibiting hormone (MIH), a neuropeptide produced in the X-organ (XO)/sinus gland (SG) complex of the eyestalk ganglia (ESG). Pulsatile release of MIH from the SG suppresses ecdysteroidogenesis by the molting gland or Y-organ (YO). The hypothesis is that nitric oxide (NO), a neuromodulator that controls neurotransmitter release at presynaptic membranes, depresses the frequency and/or amount of MIH pulses to induce molting. NO synthase (NOS) mRNA was present in Carcinus maneas ESG and other tissues and NOS protein was present in the SG. A copper based ligand (CuFL), which reacts with NO to form a highly fluorescent product (NO-FL), was used to image NO in the ESG and SG and quantify the effects of NO scavenger (1 mM cPTIO), NOS inhibitor (1 mM L-NAME), and 1 mM sodium azide (NaN3) on NO production in the SG. Preincubation with cPTIO prior to CuFL loading decreased NO-FL fluorescence ~30%; including L-NAME had no additional effect. Incubating SG with L-NAME during preincubation and loading decreased NO-FL fluorescence ~40%, indicating that over half of the NO release was not directly dependent on NOS activity. Azide, which reacts with NO-binding metal groups in proteins, reduced NO-FL fluorescence to near background levels without extensive cell death. Spectral shift analysis showed that azide displaced NO from a soluble protein in SG extract. These data suggest that the SG contains NO-binding protein(s) that sequester NO and releases it over a prolonged period. This NO release may modulate neuropeptide secretion from the axon termini in the SG.

Synthesis of 4-, 5-, 6-, and 7-Azidotryptamines

Synthesis of azidotryptamines from commercially available nitroindoles via the corresponding amino tryptamines in good overall yields (15%-38%) is presented.

Regioselective nitration of N(alpha),N(1)-bis(trifluoroacetyl)-L-tryptophan methyl ester: efficient synthesis of 2-nitro and 6-nitro-N-trifluoroacetyl-L-tryptophan methyl ester

Nitration of N(alpha),N(1)-bis(trifluoroacetyl)-l-tryptophan methyl ester with HNO(3) in acetic anhydride at 0 degrees C provides N(alpha)-trifluoroacetyl-2-nitro-l-tryptophan methyl ester in 67% yield, whereas nitration in trifluoroacetic acid at 0 degrees C gives N(alpha)-trifluoroacetyl-6-nitro-l-tryptophan methyl ester in 69% yield.

Photo-activated affinity-site cross-linking of antibodies using tryptophan containing peptides

Affinity-based conjugation methods for antibodies can produce defined and reproducible conjugates. This requires that the target antibody has an affinity site for the ligand and that the ligand has a reactive site. These requirements are critical for the conjugation of antibodies designed for diagnostic and therapeutic application. Our laboratory has discovered a novel affinity of antibodies for the amino acid tryptophan using an azido derivative of tryptophan. Here we show that tryptophan without the azido group can be photo-cross-linked to antibodies. Biotinylated tryptophan peptides are photolysed into monoclonal and polyclonal antibodies and such biotinylated antibodies are used in avidin-based ELISA. With the simple and gentle tryptophan-affinity photo-conjugation of peptides, antibodies can be conjugated with peptides to enhance their potency and expand their targeting range.

6-(Difluoromethyl)tryptophan as a probe for substrate activation during the catalysis of tryptophanase

A substrate analogue, 6-(difluoromethyl)tryptophan, was developed and characterized for mechanistic investigation of tryptophanase. The utility of this derivative was based on its ability to partition between fluoride elimination and carbon-carbon bond scission during tryptophan metabolism. The non-enzymatic hydrolysis to 6-formyltryptophan occurred slowly under neutral conditions with a first-order rate constant of 0.0039 min-1. This process, however, was accelerated by 10(4)-fold upon deprotonation of the indolyl nitrogen (N-1) at high pH. Tryptophanase did not detectably facilitate this hydrolysis reaction, since no protein-dependent conversion of the difluoromethyl group was detected. Instead, the enzyme accepted the fluorinated species as an analogue of tryptophan and catalyzed the corresponding formation of 6-(difluoromethyl)indole, pyruvate, and ammonium ion. Anionic intermediates are therefore not expected to form during the catalytic activation of the indolyl moiety. Instead, aromatic protonation likely promotes the release of indole during enzymatic degradation of tryptophan.