Loss of function of biomembranes and solubilization of membrane proteins during freezing

Isolated thylakoid membranes are damaged during freezing in dilute salt solutions, as shown by the inactivation of photochemical thylakoid reactions. After freezing, a number of membrane proteins were found in the particle-free supernatant. Up to 5% of the total membrane protein was solubilized by freezing, and the pattern of released proteins as seen in sodium dodecyl sulfate gel electrophoretograms was influenced by the nature of the solutes present. Membranes protected by sucrose did not release much protein during freezing. Concentrated salt solutions caused protein release also in the absence of freezing. Among the proteins released were ferredoxin—NADP⁺ reductase, plastocyanin and coupling factor CF₁. Subunits of CF₁ were found in different proportions in the supernatants of thylakoid suspensions after freezing in the presence of different salts. Cyclic photophosphorylation was largely inactivated before significant protein release could be detected.It is suggested that protein release is the final consequence of the non-specific suppression of intramembrane ionic interactions by the high ionic strength created in the vicinity of the membranes by the accumulation of salts during slow freezing. Salt effects on water structure and alterations of nonpolar membrane interactions by the incorporation of (protonated) lipophilic anions from organic salts into the membrane phase during freezing may also be involved.     

Major proteins of the Escherichia coli outer cell envelope membrane. Sequence of the cyanogen bromide fragments of protein I from Escherichia coli B/r.

The sequence of the cyanogen bromide fragments of one of the major outer membrane proteins of E. coli B/r has been established with the aim of elucidating the primary structure of this protein. Separation of all fragments on one molecular sieve column was achieved upon citraconylation of these fragments. Overlapping peptides were obtained by digestion of the protein, or a cyanogen bromide fragment arising from incomplete cleavage, with trypsin or Staphylococcus aureus protease.     

Formation of triton WR 1339-filled rat liver lysosomes : I. Properties and intracellular distribution of [H]Triton WR 1339

Triton WR 1339 was found to contain a high molecular weight fraction with globular polymers of ˜ 10⁵ D and a diameter of ˜80 Å (‘macrotriton’) and a low molecular weight fraction (‘microtriton’). The intracellular distribution of subfractions of [³H]Triton WR 1339 was followed by cell fractionation and by gel chromatography techniques in parallel with electron microscopy and autoradiography. Macrotriton is selectively stored in lysosomes and all evidence supports a slowly working endocytotic uptake mechanism. Microtriton permeates quickly into the cells and is rapidly and efficiently released into the bile. The data presented suggest some intracellular leaking of lysosomal contents due to the action of Triton WR 1339.     

pH gradient across the lysosomal membrane generated by selective cation permeability and Donnan equilibrium.

The pH within isolated Triton WR 1339-filled rat liver lysosomes was determined by measuring the distribution of [14C]methylamine between the intra- and extralysosomal space. The intralysosomal pH was found to be approximately one pH unit lower than that of the surrounding medium. Increasing the extralysosomal cation concentration lowered the pH gradient by a cation exchange indicating the presence of a Donnan equilibrium. The lysosomal membrane was found to be significantly more permeable to protons than to other cations. The relative mobility of cations through the lysosomal membrane is H+ greater than Cs+ greater than Rb+ greater than K greater than Na+ greater than Li+ greater than Mg2+, Ca2+. The presented data suggest that the acidity within isolated Triton WR 1339-filled lysosomes is maintained by: (1) a Donnan equilibrium resulting from the intralysosomal accumulation of nondiffusible anions and (2) a selective permeability of the lysosomal membrane to cations.     

Recovery of nitrogen fertilizer by traditional and improved rice cultivars in the Bhutan Highlands

The recovery of soil derived nitrogen (N_DFS) and fertilizer N (N_DFF) was investigated in highland rice (Oryza sativa L.) fields in Bhutan, characterized by high inputs of farmyard manure (FYM). The effect of 60 kg N ha^?1 (60 N) applied in two splits to a traditional and an improved cultivar, popular among the farmers, was investigated using the ¹⁵N isotope dilution technique. No differences were found between cultivars with respect to the uptake of N_DFS and N_DFF, but the improved cultivar yielded 27% more (P?≤?0.05) grain compared with the traditional cultivar. This was largely due to its greater harvest index (HI). The mean percentage recovery of fertilizer N (REN) applied at 45 days after transplanting (DAT) was 34% compared to 22% at 7 DAT, resulting in 56% greater uptake of N_DFF at 45 DAT. The overall REN for both the improved and the traditional cultivars were 25.7% and 30% respectively, with no difference between cultivars, but REN decreased with increasing FYM inputs. Fertilizer N recommendations that allow for previous FYM inputs combined with applications timed to coincide with maximum crop demand (45 DAT), and the use of improved cultivars, could enhance N fertilizer recoveries (REN) and increase rice yields in the Bhutan Highlands.     

Eosin staining of gelatine

Summary The mechanism of gelatine staining with four selected fluorone derivative dyes (eosin y, ethyl eosin, methyl eosin, uranin) was investigated. Gelatine films were stained in dye-buffer-ethanol solutions at varying pH and in the presence of NaCl and urea. Dye binding was recorded spectrophotometrically. Ionization constants of auxochromic phenolic groups were determined from pH-absorbance curves of dye-buffer-ethanol solutions. Dyebinding was greatest at pH below pK_OH and decreased with increasing pH. The addition of NaCl reduced dye binding slightly below pK_OH but markedly above pK_OH. The addition of 8 M urea decreased dyebinding regardless of pH. Comparing the pH dependence of dyebinding for eosin y and esterified eosins with ionization constants revealed that ionic bonding is unlikely to occur at the carboxyl group as well as at the phenolic group. Dye binding is intimately related to the presence of Br-groups. These results are discussed in conjunction with the functional structure of the dye ions and current concepts of dyebinding mechanisms.     

Innate immunity orchestrates the mobilization and homing of hematopoietic stem/progenitor cells by engaging purinergic signaling—an update

Purinergic Signalling - Bone marrow (BM) as an active hematopoietic organ is highly sensitive to changes in body microenvironments and responds to external physical stimuli from the surrounding...