Enhanced stability of maize endosperm ADP-glucose pyrophosphorylase is gained through mutants that alter subunit interactions

Temperature lability of ADP-glucose pyrophosphorylase (AGP; glucose-1-phosphate adenylyltransferase; ADP: alpha-D-glucose-1-phosphate adenylyltransferase, EC 2.7.7.27), a key starch biosynthetic enzyme, may play a significant role in the heat-induced loss in maize seed weight and yield. Here we report the isolation and characterization of heat-stable variants of maize endosperm AGP. Escherichia coli cells expressing wild type (WT) Shrunken2 (Sh2), and Brittle2 (Bt2) exhibit a reduced capacity to produce glycogen when grown at 42 degreesC. Mutagenesis of Sh2 and coexpression with WT Bt2 led to the isolation of multiple mutants capable of synthesizing copious amounts of glycogen at this temperature. An increase in AGP stability was found in each of four mutants examined. Initial characterization revealed that the BT2 protein was elevated in two of these mutants. Yeast two-hybrid studies were conducted to determine whether the mutant SH2 proteins more efficiently recruit the BT2 subunit into tetramer assembly. These experiments showed that replacement of WT SH2 with the heat-stable SH2HS33 enhanced interaction between the SH2 and BT2 subunits. In agreement, density gradient centrifugation of heated and nonheated extracts from WT and one of the mutants, Sh2hs33, identified a greater propensity for heterotetramer dissociation in WT AGP. Sequencing of Sh2hs33 and several other mutants identified a His-to-Tyr mutation at amino acid position 333. Hence, a single point mutation in Sh2 can increase the stability of maize endosperm AGP through enhanced subunit interactions.     

Superconducting magnets for the CBA project

The superconducting magnets that were designed and tested for the BNL colliding beam accelerator are described, including dipoles, quadrupoles and trim coils. The dipoles had an effective length of 436 cm, a good field aperture of 8.8 cm diameter, and were designed for an operating field of 5.28 T in a temperature range between 2.6 K and 3.8 K (provided by supercritical helium). The quadrupoles had the same aperture, an effective length of 138.5 cm, and were designed to operate in series with the dipoles, with a gradient of 70.8 T/m. The dipoles incorporated internal sextupole, octupole, and decapole trim coil windings; the quadrupole trim coils consisted of dipole, quadrupole, and dodecapole windings. The design, construction, and performance (training, field quality, quench protection characteristics) of prototype magnets are discussed in considerable detail.     

Effects of intentionality and strategy on memory for frequency.

Several studies have examined whether Ss who learn a list of words incidentally remember frequency as well as those who learn the words intentionally. Conflicting results have been found. This discrepancy is examined in the present 3 experiments with a total of 105 undergraduates. Results of Exps I and II indicate that intentional-learning Ss exhibited an advantage in memory for frequency only if the instructions emphasized the importance of good performance on the memory task. Results of Exp III show that intentionality influenced memory for frequency within a list of items and that a strategy that involved semantic processing led to improved frequency estimation. It is concluded that these results are inconsistent with formulations of the claim that frequency information is encoded automatically and demonstrate that instructions play a crucial mediating role in memory for frequency. (55 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Polarisation-independent 20 Gbit/s soliton data transmission over12500 km using amplitude and phase modulation soliton transmissioncontrol

Polarisation-independent error-free 20 Gbit/s soliton data transmission over 12500 km with flat system Q dependence on distance, has been demonstrated using static filtering and a semiconductor polarisation-independent amplitude and phase modulator for soliton transmission control     

Changes in global stability and local structure of cytochrome c upon substituting phenylalanine-82 with tyrosine

We have examined the F82Y;C102T variant of Saccharomyces cerevisiae iso-1-cytochrome c using high-resolution proton nuclear magnetic resonance spectroscopy, chemical denaturation, and differential scanning calorimetry. Comparison of proton chemical shifts, paramagnetic shifts, and nuclear Overhauser effects indicates structural changes are localized to the vicinity of position 82. One alteration involves the rearrangement of the side chain of leucine-85. Using many more proton assignments than were available in the initial report [G. J. Pielak, R. A. Atkinson, J. Boyd, and R. J. P. Williams, Eur. J. Biochem. 177, 179-185 (1988)], a second alteration involving an interaction between arginine-13 and tyrosine-82 is observed. The interaction appears to involve a hydrogen bond with the eta-protons of arginine's guanido group acting as donor and tyrosine's phenolic eta-oxygen as acceptor. In spite of this potentially-stabilizing interaction, the free energy of denaturation decreases by approximately 2.4 kcal mol-1. Results are discussed with respect to alterations in the native and denatured states.     

Ring-opening polymerization of norbornene and six of its methyl derivatives by well-defined tungsten-carbene complex catalysts

Eight tungsten-carbene complex catalysts of the type W(CHCMe₃)L¹L²L³L⁴, where the ligands L are various combinations of OCH₂CMe₃, SO₃CF₃, OSiPh₃, Br and I, have been used, in the presence and absence of GaBr₃, to polymerize norbornene and six of its methyl derivatives by ring opening. The microstructure of the polymers was determined from their ¹³C NMR spectra; values of cis content, cis-trans blockiness, ring-dyad tacticity and head-tail bias were derived as appropriate to each system. The results are discussed in terms of electronic and steric effects in the propagating carbene complexes.     

Ethnicity and MMPI performance: A review.

Minnesota Multiphasic Personality Inventory (MMPI) performance as a function of ethnic group membership was reviewed in Asian Americans, Blacks, Hispanics, and Native Americans. There did not appear to be a simple relation between ethnic group membership and MMPI performance, either within or between such populations as normal individuals, psychiatric patients, prisoners, or substance abuse patients. Moderator variables, such as social class, education, and type of setting, seem to play an important role in determining the specific pattern of scores that are found. There is a paucity of studies that have investigated whether there are any empirical correlates of the obtained differences when two ethnic groups are compared on the MMPI, that is, investigations of the external validity of the MMPI in various ethnic groups. It seems premature to conclude that new norms for the MMPI are needed for specific ethnic groups without additional research that examines the issues raised in this review. (PsycINFO Database Record (c) 2010 APA, all rights reserved)