Additional Accessory Research Articles

Amphibole-rich clots in calc-alkalic granitoids in the Borborema province, northeastern Brazil

Metaluminous granodioritic–tonalitic plutons intruded low-grade metaturbidites of the Cachoeirinha–Salgueiro terrane and low- to intermediate-grade metasediments of the Macururéterrane, northeastern Brazil, around 630 Ma ago. Four types of amphibole-rich polycrystalline clots, up to 20 cm long, are found within mafic microgranular enclaves or in their granodioritic–tonalitic hosts. Type-I clots are usually angular, with granoblastic textures, composed of amphibole with patchy actinolite cores and magnesiohornblende margins, in polygonal packing where grains commonly display near-120° triple junctions. Interstitial biotite and calcic clinopyroxene are the other component phases. Magnesiohornblende+biotite cumulates form the type-II clots that sometimes constitute an external layer around type-I clots. Actinolite pseudomorphs after clinopyroxene-rich restites form the type-III. A fourth type, texturally similar to type-I clot, contains pyrite as an additional accessory phase and is found only in plutons in the Macururéterrane. Amphibole cores in clots of types I and IV are actinolite with SiO 2 around 55%, MgO (6.5%, FeO 10.5% and Al 2O 3 around 2%, while margins are magnesiohornblende with SiO 2 around 50%, FeO≈12%, MgO≈14.5%, and Al 2O 3≈5%). Amphibole aggregates in type-II clots display compositions identical to those in the granodiorite hosts. Biotite in types I and IV clots show SiO 2, TiO 2, K 2O and CaO equivalent to those in the granodiorite host, but are about 4% lower in FeO and about 3% higher in MgO. Although all studied plutons are oxidized I-type granites, those from the Cachoeirinha–Salgueiro terrane display quartz-corrected w.r. δ 18O (+11 to +13‰ SMOW) in the range for S-type granites, while in the Macururéterrane values from +9 to +10‰ are observed. Amphibole-rich clots usually have δ 18O values 1.5‰ lower than those observed in their corresponding hosts. Initial Sr ratios for plutons and their mafic microgranular enclaves are 0.70598 in the Cachoeirinha–Salgueiro terrane. Host plutons show εNd (0.6 Ga) values from −1.0 to −3.0 and −4.6 to −6.7, respectively in the Cachoeirinha–Salgueiro and Macururéterranes, and δ 34S from +1 to +9‰CDT in the Cachoeirinha–Salgueiro terrane. Whole-rock δD values for amphibole clot-bearing granodiorites, mafic microgranular enclaves and clots vary from −69 to −114‰ SMOW, a variation much broader than for corresponding δ 18O values. Partial fusion of low-T altered basaltic source (amphibolites) generated the calc-alkalic granodioritic–tonalitic magmas in the Cachoeirinha–Salgueiro terrane. Type-I clots are probably fragments or restites of melting of this source. High δ 18O in amphibole-rich clots and granodiorite hosts support this hypothesis. Actinolite pseudomorphs after calcic clinopyroxene (type-III clots) attest to the incorporation of extraneous H into host magmas, causing a wide δD isotopic range. In the Macururéterrane, type-IV amphibole-rich clots are restite remnants of dehydration melting of an amphibolite source.

Transport vesicle docking: SNAREs and associates.

Proteins that function in transport vesicle docking are being identified at a rapid rate. So-called v- and t-SNAREs form the core of a vesicle docking complex. Additional accessory proteins are required to protect SNAREs from promiscuous binding and to deprotect SNAREs under conditions in which transport vesicle docking should occur. Because access to SNAREs must be regulated, other proteins must also contain specificity determinants to accomplish delivery of transport vesicles to their distinct and specific membrane targets.

Hydroxyl radical footprints and half-site arrangements of binding sites for the CysB transcriptional activator of Salmonella typhimurium

CysB is a transcriptional activator for the cysteine regulon and negatively autoregulates its own gene, cysB. Transcription activation also requires an inducer, N-acetyl-L-serine. CysB is known to bind to activation sites just upstream of the -35 regions of the positively regulated cysJIH, cysK, and cysP promoters and to a repressor site centered at about +1 in the cysB promoter. Additional accessory sites have been found in positively regulated promoters. The hydroxyl radical footprinting experiments reported here indicate that the activation sites CBS-J1, CBS-K1, and CBS-P1 in the cysJIH, cysK, and cysP promoters are composed of two convergently oriented 19-bp half-sites separated by 1 or 2 bp. N-Acetyl-L-serine stimulates binding to these sites as well as to the accessory sites CBS-J2 and CBS-P2, both of which share a similar topology with activation sites. A second topology is found in the accessory site CBS-K2 and the repressor site CBS-B, which contain divergently oriented 19-bp half-sites separated by one or two helical turns. N-Acetyl-L-serine inhibits binding to these two sites. A third topology is present in the cysK and cysP promoters, where an additional half-site is oriented toward the activation site and separated from it by one helical turn. Here, CysB binds to all three half-sites, bending the DNA, and N-acetyl-L-serine decreases the extent of bending. The marked dissimilarities of these half-site arrangements and of their responses to N-acetyl-L-serine suggest that CysB, a homotetramer, binds to them with different combinations of subunits.

Bivalent opioid peptides synthesized from μ selective monomers display preferential selectivity for δ receptors

A series of dimeric opioid peptides derived from μ selective compounds was synthesized to investigate whether μ and δ receptors coexist as distinct recognition sites on the same receptor complex. Some compounds were several times more potent than the corresponding monomers in the MVD (mouse vas deferens) smooth muscle preparation, which is rich in δ receptors, but yet retaining substantial activity in the GPI (guinea pig ileum). It is suggested that δ receptors might differ from μ receptors in that they possess an additional accessory recognition site, to which could bind a particular amino acid residue present in the second halves of these bivalent ligands. This residue could play the role of “address” at δ opioid receptors.

A gradient valve for HPLC

A novel concept of a low-pressure single gradient mixing pump is described. The solvents are mixed via a two-way switching valve of special design. Due to a mechanical transmission between the pump piston and the gradient valve rotor, the precise partitioning of the both liquids is achieved regardless of a nonlinear piston refill period. The use of this concept has no limitations for specially constructed pumps equipped with stepping motors and with position encoders for piston displacement. For isocratic elution with mixed solvents it is possible to set manually any binary composition without the need of any additional accessory.

Identical twins with differing forms of ventricular pre-excitation.

Identical 10-year-old twins, both with electrocardiograms showing a short PR interval and a normal QRS complex but with dramatically different electrophysiological characteristics, are described. One twin experienced episodes of rapid palpitation and on one occasion was resuscitated from ventricular fibrillation. An intracardiac electrophysiological study confirmed the presence of an atrioventricular nodal bypass tract and in addition revealed the presence of an accessory atrioventricular pathway, thus demonstrating that the patient had both the Lown-Ganong-Levine and Wolff-Parkinson-White syndromes. Re-entry tachycardia and atrial fibrillation, with a very rapid ventricular rate, were precipitated. After treatment with amiodarone, the patient became asymptomatic and a repeat study showed that the features of the atrioventricular nodal bypass tract were no longer present and though re-entry tachycardias using the accessory atrioventricular pathway could still be induced, their rates were slower than before treatment. The other twin, in spite of an identical surface electrocardiogram, was asmymptomatic. An electrophysiological study showed the features of an atrioventricular nodal bypass tract but there was no evidence of additional atrioventricular accessory connections and a tachycardia could not be induced.

SOME TERRESTRIAL RELATIONS AND MINERALS OF METEORITES*

AbstractThis paper consists of two parts. In part “I. Terrestrial Relations,” the first three pages of Chapter 14 of Farrington's Meteorites are quoted and discussed, and four conclusions concerning the occurrence of minerals in meteorites are reached. In part “II. Minerals,” two additional secondary accessory or Class III meteoritic minerals are recognized and tabulated — the carbonate calcite and the sulfide millerite. The following three minerals also are commented on: chlorite, which is almost certainly not a true meteoritic mineral; pentlandite, which may eventually be discovered in meteorites; and “peckhamite,” which is doubtless nothing other than an intimate mixture of bronzite or hypersthene and olivine. Three types of minerals found in meteorites — cosmic, terrestrialized, and extraneous — are defined and considered.