Reversible inactivation of soluble liver guanylate cyclase by disulfides

A new amino acid was isolated from the cuticle collagen of $\text{Ascaris lumbricoides}$ and characterized by ultraviolet, mass and nmr spectroscopies and chemical degradation. The results indicate that the compound is an isomer of trityrosine, having an ether linkage. The name “isotrityrosine” is proposed. Its structure suggests that it serves as a crosslink and plays a role in the organization of the collagen structure.     

Differential effect of buffer on the spin trapping of nitric oxide by iron chelates.

Nitric oxide synthase (NOS) generates nitric oxide (NO*) by the oxidation of l-arginine. Spin trapping in combination with electron paramagnetic resonance (EPR) spectroscopy using ferro-chelates is considered one of the best methods to detect NO* in real time and at its site of generation. The spin trapping of NO* from isolated NOS I oxidation of L-arginine by ferro-N-dithiocarboxysarcosine (Fe(DTCS)2) and ferro-N-methyl-d-glucamide dithiocarbamate (Fe(MGD)2) in different buffers was investigated. We detected NO-Fe(DTCS)2, a nitrosyl complex, resulting from the reaction of NO* and Fe(DTCS)2, in phosphate buffer. However, Hepes and Tris buffers did not allow formation of NO-Fe(DTCS)2. Instead, both of these buffers reacted with Fe2+, generating sparingly soluble complexes in the absence of molecular oxygen. Fe(DTCS)2 and Fe(MGD)2 were found to inhibit, to a small degree, NOS I activity with a greater effect observed with Fe(MGD)2. In contrast, Fe(MGD)2 was more efficient at spin trapping NO* from the lipopolysaccharide-activated macrophage cell line RAW264.7 than was Fe(DTCS)2. Data suggested that Fe(DTCS)2 and Fe(MGD)2 are efficient at spin trapping NO* but their maximal efficiency may be affected by experimental conditions.     

A model for glucose metabolism in energy-sufficient bacterial cultures

Summary A model for uncoupled glucose uptake under energy-sufficient conditions is presented. The model is derived from glucose catabolic pathways. The resulting model predicts specific glucose uptake rate as a function of both growth rate and extracellular glucose concentration. This prediction is consistent with reported literature data.     

Heme spin states and peroxide-induced radical species in prostaglandin H synthase

We have examined the optical, magnetic circular dichroism, and electron paramagnetic resonance (EPR) spectra of pure ovine prostaglandin H synthase in its resting (ferric) and ferrous states and after addition of hydrogen peroxide or 15-hydroperoxyeicosatetraenoic acid. In resting synthase, the distribution of heme between high- and low-spin forms was temperature-dependent: 20% of the heme was low-spin at room temperature whereas 50% was low-spin at 12 K. Two histidine residues were coordinated to the heme iron in the low-spin species. Anaerobic reduction of the synthase with dithionite produced a high-spin ferrous species that had no EPR signals. Upon reaction with the resting synthase, both hydroperoxides quickly generated intense (20-40% of the synthase heme) and complex EPR signals around g = 2 that were accompanied by corresponding decreases in the intensity of the signals from ferric heme at g = 3 and g = 6. The signal generated by HOOH had a doublet at g = 2.003, split by 22 G, superimposed on a broad component with a peak at g = 2.085 and a trough at g = 1.95. The lipid hydroperoxide generated a singlet at g = 2.003, with a linewidth of 25 G, superimposed on a broad background with a peak at g = 2.095 and a trough around g = 1.9. These EPR signals induced by hydroperoxide may reflect synthase heme in the ferryl state complexed with a free radical derived from hydroperoxide or fragments of hydroperoxide.     

Is the binding of magnesium (II) to calmodulin significant? An investigation by magnesium-25 nuclear magnetic resonance

Previous reports on the interaction between calmodulin (CaM) and Mg2+ range from no binding to a binding constant of 10(4) M-1 [for a summary, see Cox, J. A., Comte, M., Malnoe, A., Berger, D., & Stein, E. A. (1984) Met. Ions Biol. Syst. 17, 215-273]. In order to resolve the controversy, we used 25Mg NMR to study the binding of Mg2+ to apo-CaM, CaM.Ca2(2)+ (in which sites III and IV are occupied by Ca2+), CaM.La2(3)+ (in which sites I and II are occupied by La3+), and the two tryptic fragments of calmodulin, TR1C (containing sites I and II of CaM) and TR2C (containing sites III and IV of CaM). In each system, a "titration set" and a "temperature set" were obtained, and the spectral data were analyzed by total band-shape analysis to calculate the association constant (Ka) and off-rate (koff). As in the case of Ca2+ binding, sites I and II and sites III and IV were treated as two sets of equivalent sites, and a Ca2+/Mg2+ competition experiment suggested that Mg2+ competes with Ca2+ for the same sites. For both CaM.Ca2(2)+ and TR1C, moderately large Ka (2000 and 3500 M-1, respectively) and moderate off-rates (koff = 2300 and 3000 s-1, respectively, at 25 degrees C) were observed. For both CaM.La2(3)+ and TR2C, binding of Mg2+ was weaker by a factor of ca. 10 (Ka = 300 and 200 M-1, respectively) while the off-rates were also moderate (koff = 3500 and 2200 s-1, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)