Bacterial Activity Associated with the Decomposition of Woody Substrates in a Stream Sediment

Ground bark and heartwood from Alnus rubra and Pseudotsuga menziesii were added to a muddy sediment from a small Oregon stream and incubated in situ. Carbon dioxide and methane production rates were increased by all amendments, the biggest increase being shown with A. rubra wood. Except for sediment amended with A. rubra wood, nitrogen fixation rates from all treatments (including the control) were approximately 0.1 nmol/g per h throughout the 6-month study period. Contrary to expectations, neither bark had a noticeable adverse effect on microbial activity, but the A. rubra wood promoted nitrogen fixation. These results help to explain the faster rate of decomposition of A. rubra wood in water compared with that of P. menziesii described in the literature. The uptake kinetics of glucose (V_max) did not follow the same pattern as gas evolution.     

Stimulation of eicosapentaenoic acid metabolism in washed human platelets by 12-hydroperoxyeicosatetraenoic acid

Washed human platelets were not able to convert eicosapentaenoic acid (EPA) to thromboxane B3 (TXB3) and 12-hydroxyeicosapentaenoic acid (AA) to washed human platelets induced conversion of EPA to TXB3 and 12-HEPE. Esculetin, a specific inhibitor of 12-lipoxygenase, prevented the effect of AA, but cyclooxygenase inhibitor did not. The conversion of AA to TXB2 was not affected by the same dose of esculetin. These data suggest that products of AA formed by 12-lipoxygenase in human platelets have stimulatory effects on EPA metabolism. When AA was preincubated with washed human platelets, its effect on EPA conversion was reduced, suggesting that a labile product of AA formed by 12-lipoxygenase is involved in the facilitation of EPA metabolism. Addition of 12-hydroperoxyeicosatetraenoic acid directly to washed human platelets caused dose-dependent synthesis of TXB3 and 12-HEPE, while addition of 12-hydroxyeicosatetraenoic acid had no effect. Thus, 12-hydroperoxyeicosatetraenoic acid formed from AA promotes the metabolism of EPA in washed human platelets.     

Dichroism of bacteriochlorophyll in cells of the photosynthetic bacterium Rhodopseudomonas palustris

1. The dichroism was measured at varied wavelengths of polarized light in “intact” cells of Rhodopseudomonas palustris and in films of air-dried lamellar fragments of the bacterium.     

Localization of Myoglobin in Striated Muscle of the Domestic Pig; Benzidine and NADH2-TR Reactions

Tissue blocks 1 cm³ from longissimus (white) and trapezius (red) muscles of adult pigs were fixed in phosphate-buffered 2.5% glutaraldehyde, pH 7.4, for 4 hr at about 25 C; washed 4 hr in running tap water, and immersed in 30% w/v sucrose solution for 16 hr or more. After freezing in liquid N₂, cryostat sections were cut and floated into saturated aqueous benzidine containing 0.15% H₂O₂ at 25 C for 30 min. Stained sections were washed in distilled water and mounted on slides with glycerol jelly. Three distinguishable gradiations of color intensity were found: strong, intermediate, and negative. The trapezius had a greater number of myoglobin-positive fibers than the longissimus muscle. Myoglobin-positive and myoglobin-negative staining occurred in red and white fibers, respectively; intermediates were apparently more closely related to the red than to the white fibers. The NADH₂TR reaction showed the same sites as did the benzidine reaction.     

Crystal structure of plakalbumin, a proteolytically nicked form of ovalbumin. Its relationship to the structure of cleaved alpha-1-proteinase inhibitor

The crystal structure of plakalbumin, a proteolytically nicked form of ovalbumin, has been determined to a resolution of 2.8 A by the isomorphous replacement method and preliminary refinement. The structure closely resembles that of the cleaved form of alpha-1-proteinase inhibitor, with some important exceptions. The disposition of the new carboxyl chain terminus liberated by proteolysis is different with respect to the central beta-sheet A in the structures of these two molecules. In alpha-1-proteinase inhibitor, the new chain terminus inserts in beta-sheet A to add a middle strand to the sheet. In plakalbumin, this strand remains free near the site at which the cleavage occurs. A structural basis for this difference in behavior is proposed from the structures and sequences of these two molecules and other members of the serpin family. The structures and positions of the putative signal peptide of ovalbumin, the several post-translational modifications, and the relationship of the intron-exon patterns of plakalbumin and alpha-1-proteinase inhibitor to their protein structures are also described.     

甘蔗幼叶切段培养中的体细胞胚胎发生

本文从形态学和组织学方面研究了甘蔗幼叶胚性愈伤组织发生及体细胞胚胎的形成过程。甘蔗幼叶片切段培养于含2.4—D1.5mg/1的MS培养基上,4—6天后切段开始形成愈伤组织,约10天后愈伤组织表面出现白色颗粒状结构。将含有白色颗粒状结构的愈伤组织转移至不含激素的培养基中,7—10天后可见有小植株长出。组织学和形态学观察表明,甘蔗离体再生植株是通过体细胞胚胎发生途径。