Determination of the sedimentation constants for total suspended solids and the algal component in a full-scale primary facultative pond operating at high wind velocities under tropical conditions

This study evaluated the amount, distribution and sedimentation constant of solids in a full-scale primary facultative pond operating mostly under high wind conditions and the contribution made by the algal biomass. Solids deposition rates were measured using sedimentation traps placed in the inlet and outlet zones of the pond. Most sludge accumulation occurred, not surprisingly, in the inlet zone A1 with a sludge volume of 9072 m3 accumulating over an operating time of approximately 3 years. However, sludge deposition within this zone was uneven and affected by wind action. Mean proportionality constant (K) values for solids sedimentation were 3.02 and 5.70 for depths of 50 cm and 100 cm respectively for A1. In contrast in zone A3, (the outlet zone), reduced K values of 1.38 and 3.22 were obtained for depths of 50 cm and 100 cm respectively. The algal sedimentation constant varied from 0.8 d−1 in zone A1 to 0.02 d−1 in A3. These data suggest that in this large facultative pond the wind, blowing predominantly from the direction of the outlets towards the pond inlets, had a greater influence on solids deposition than the bulk hydraulic flow and also kept the pond completely mixed for most of the time.

The RNase P Associated with HeLa Cell Mitochondria Contains an Essential RNA Component Identical in Sequence to That of the Nuclear RNase P

ABSTRACT The mitochondrion-associated RNase P activity (mtRNase P) was extensively purified from HeLa cells and shown to reside in particles with a sedimentation constant (∼17S) very similar to that of the nuclear enzyme (nuRNase P). Furthermore, mtRNase P, like nuRNase P, was found to process a mitochondrial tRNASer(UCN)precursor [ptRNASer(UCN)] at the correct site. Treatment with micrococcal nuclease of highly purified mtRNase P confirmed earlier observations indicating the presence of an essential RNA component. Furthermore, electrophoretic analysis of 3′-end-labeled nucleic acids extracted from the peak of glycerol gradient-fractionated mtRNase P revealed the presence of a 340-nucleotide RNA component, and the full-length cDNA of this RNA was found to be identical in sequence to the H1 RNA of nuRNase P. The proportions of the cellular H1 RNA recovered in the mitochondrial fractions from HeLa cells purified by different treatments were quantified by Northern blots, corrected on the basis of the yield in the same fractions of four mitochondrial nucleic acid markers, and shown to be 2 orders of magnitude higher than the proportions of contaminating nuclear U2 and U3 RNAs. In particular, these experiments revealed that a small fraction of the cell H1 RNA (of the order of 0.1 to 0.5%), calculated to correspond to ∼33 to ∼175 intact molecules per cell, is intrinsically associated with mitochondria and can be removed only by treatments which destroy the integrity of the organelles. In the same experiments, the use of a probe specific for the RNA component of RNase MRP showed the presence in mitochondria of 6 to 15 molecules of this RNA per cell. The available evidence indicates that the levels of mtRNase P detected in HeLa cells should be fully adequate to satisfy the mitochondrial tRNA synthesis requirements of these cells.

Structural Investigation of Invertebrate Hemoglobins Using the Stem

Scanning transmission electron microscopy (STEM) was used to study the structure of the extracellular hemoglobins of the annelids Lumbricus, Arenicola, and Nephtys. These are giant molecules, possessing a molecular weight of 3-4 x IO6,a sedimentation constant of about 60s and consisting of about five to seven different polypeptide chains (1,2,3). The samples were diluted to 100-200μg/ml with distilled water just before application to a very thin(∽15Å) carbon substrate supported on a microgrid. One percent (w/v) uranyl acetate solution was used for negative staining for 2 min. and dried in air. The specimens were examined with an electron energy of 22-35keV.

Isolation and properties of an RNA fraction present in Brucella culture supernatants

SUMMARYThe supernatant fluids of batch and continuous cultures of Brucella strains contained up to 100 mg/i of soluble RNA which could be recovered by precipitation with lysozyme. This RNA fraction had many of the properties of ribosomal RNA and was single-stranded, sensitive to ribonuclease, with an approximate sedimentation constant of 5S, a molecular weight of about 35000 daltons and an adenine; guanine; cytosine; uracil content of 17·5 26·5 33; 23 mol% respectively. RNA fractions from lysozyme precipitates evoked high titres of Brucella agglutinins on injection into rabbits and induced acute inflammatory responses in guinea-pig skin. Highly purified RNA fractions prepared by phenol extraction of lysozyme precipitates did not evoke antibodies to Brucella abortus.