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H Axelrod

Publications and source records attributed to H Axelrod.

15 recordsLinked to original sources
PubMed2002

Double mutant studies identify electrostatic interactions that are important for docking cytochrome c2 onto the bacterial reaction center.

Cytochrome c2 (cyt) is the mobile electron donor to the reaction center (RC) in photosynthetic bacteria. The electrostatic interactions involved in the dynamics of docking of cyt onto the RC were examined by double mutant studies of the rates of electron transfer between six modified Rhodobacter sphaeroides RCs in which negatively charged acid residues were replaced with Lys and five modified Rhodobacter capsulatus Cyt c2 molecules in which positively charged Lys residues were replaced with Glu. We measured the second-order rate constant, k2, for electron transfer from the reduced cyt to the oxidized primary donor on the RC, which reflects the energy of the transition state for the formation of the active electron transfer complex. Strong interactions were found between Lys C99 and Asp M184/Glu M95, and between Lys C54 and Asp L261/Asp L257. The interacting residues were found to be located close to each other in the recently determined crystal structure of the cyt-RC complex [Axelrod, H., et al. (2002) J. Mol. Biol. (in press)]. The interaction energies were approximately inversely proportional to the distances between charges. These results support earlier suggestions [Tetreault, M., et al. (2001) Biochemistry 40, 8452-8462] that the structure of the transition state in solution resembles the structure of the cyt-RC complex in the cocrystal and indicate that specific electrostatic interactions facilitate docking of the cyt onto the RC in a configuration optimized for both binding and electron transfer. The specific interaction between Asp M184 and Lys C99 may help to nucleate short-range hydrophobic contacts.

Cytochrome c Group↗
PubMed1990

Studies on the bioecological aspects of adult mosquitoes in the Prado Basin of southern California.

Studies on the bionomics of adult mosquitoes were carried out in the Prado Basin of southern California during 1985-86. The faunal composition of mosquitoes caught by species was (in descending order) Culex quinquefasciatus, Cx. tarsalis, Cx. erythrothorax, Cx. stigmatosoma (formerly Culex peus) followed by Anopheles freeborni, Culiseta particeps, Cs. inornata and Cs. incidens. The number of mosquitoes per trap night was the lowest during December through February, and the highest during August through October. Depending on both intrinsic and extrinsic factors, adult mosquitoes were active at dusk and dawn. In spatial distribution studies, both adult and larval collections showed that Cx. quinquefasciatus and Cx. stigmatosoma were associated with dairy lagoons and Cx. erythrothorax with duck ponds and a nearby wooded area. Culex tarsalis was found in greater number at all habitats. Anopheles freeborni and Culiseta spp. were found around the wooded area. In vertical distribution studies, more mosquitoes were captured at the highest (6 m) level than at lower (0.6 and 3 m) levels which was probably due to the large percentage of parous females present at this site.

Animals↗
PubMed1988

Efficacy and longevity of Bacillus sphaericus 2362 formulations for control of mosquito larvae in dairy wastewater lagoons.

Bacillus sphaericus strain 2362 was evaluated for the control of Culex larvae in dairy wastewater lagoons. Both initial and long-term efficacy were studied. Two primary powder preparations of ABG-6184 yielded mediocre and short-term control at the rates of 0.25 and 0.5 lb/acre (0.26 and 0.56 kg/ha), while level of control and persistence greatly increased as the dosages were increased to 1.0, 2.0 and 4.0 lb/acre (1.12, 2.24 and 4.48 kg/ha). The 1.0 and 2.0 lb/acre rates yielded almost 100% control for 4 weeks and the 4.0 lb/acre rate yielded control (99%) for 49 days or longer. A flowable concentrate preparation (BSP-2) yielded complete initial and persistent control of larvae for 14-21 days at 2.0, 4.0 and 5.0 lb/acre (2.24, 4.49 and 5.6 kg/ha). Granular formulations of B. sphaericus 2362 (ABG-6185) were also evaluated at 2.5, 5.0, 7.5, 10.0 and 20.0 lb/acre (2.8, 5.6, 8.4, 11.2 and 22.4 kg/ha) of the granules. Some of the formulations were more active than the others, yielding excellent initial and persistent control (80% +) for 14-21 days with one treatment.

Animals↗
PubMed1986

X-ray studies of nucleotide binding and pyridoxal phosphate labeling of the gene 5 DNA unwinding protein.

X-ray diffraction studies have been carried out using difference Fourier methods to evaluate the reaction or interaction of an affinity label and 5'-phosphate nucleotides with the gene 5 DNA binding protein in the crystalline state. In the first case the crystalline protein was reacted with pyridoxal phosphate. Pyridoxal phosphate, which has served as an affinity label for nucleotide binding sites on other enzymes, demonstrated a major site of substitution at the center of the protein's DNA binding cleft adjacent to lysine 46 as well as two other reaction sites near residues implicated in DNA binding. Difference Fourier maps of crystals exposed to 5'-dAMP, 5'-dCMP and 5'-dTMP indicated that phosphate groups were associated with most lysine and arginine side-chains on the surface of the protein but that the nucleoside portion of the ligands were generally disordered. In several cases, however, more specific binding of the nucleotides appeared to have occurred and these sites were primarily within the proposed DNA binding cleft of the protein. In particular, binding was observed near tyrosine 34, phenylalanine 73 and within the curl of the DNA binding loop containing tyrosine 26.

Adamantane↗
PubMed1986

An experiment regarding crystallization of soluble proteins in the presence of beta-octyl glucoside.

Twenty-one soluble proteins, five tRNAs, and three protein-nucleic acid complexes were studied in a systematic manner with regard to their crystallization behavior from polyethylene glycol and ammonium sulfate solutions in the presence of 0 to 1.5% beta-octyl glucoside. Our observations suggest that this neutral detergent does influence in a very positive way the growth characteristics of the macromolecules included in this experiment. In general, more reproducible and rapid growth was noted with an increased number of large individual crystals at the expense of microcrystals. In several cases, new crystal forms were discovered. Selected x-ray diffraction analyses imply that crystals grown in the presence of beta-octyl glucoside diffract as well or better than those grown in its absence. In addition, a screen of two proteins grown in the presence of 14 different common detergents suggested that a general detergent effect may be beneficial for the growth of crystals of biological macromolecules.

Crystallization↗