Structural and functional studies of ribonucleoprotein fragments isolated from Escherichia coli 50 S ribosomal subunits.

Ribonuclease digestion of 50 S-derived LiCl cores led to 22 ribonucleoprotein particles which were isolated by repeated sucrose gradient centrifugations. The protein content was determined and ranged from 2 to 28 proteins. Most of the fragments showed a unique RNA pattern as judged by acrylamide gel electrophoresis.Functional tests were performed with selected fragments. No fragment was active in the poly(U) or the peptidyl-transferase assay. Chloramphenicol binding studies revealed that in addition to the dominant role of protein L16, the protein L11 (or L6) is involved directly in the drug binding. Finally, tests for ATPase and GTPase activity showed that protein L18 is involved in GTPase activity.     

Segmental norepinephrine and dopamine levels in cat spinal cord

Tissue levels of norepinephrine in the uninjured cat were determined by a fluorimetric or enzymatic radiometric assay technique. There were no significant differences of NE levels between the two techniques. The highest concentrations of NE were found in the cervical (.170 ug/g) and lumbar (.232 ug/g) enlargements and appear to be related to the relative amount of grey and white matter present at these levels. Dopamine levels, as determined by the enzymatic radiometric assay technique, were found to be low in those spinal segments measured (less than 0.030 ug/g). DA appears to be similarly distributed as norepinephrine in the spinal segments. Barbiturate or nitrous oxide anesthetic agents did not result in significant differences in NE determinations at cervical or thoracic segments. Variability of reported NE and DA levels from other studies appears to be related to differences in assay technique.     

Immunohistochemical localization of dynorphin (1-8) in hypothalamic magnocellular neurons: evidence for absence of proenkephalin

Dynorphin(1-8) immunoreactivity was visualized by immunohistofluorescence in hypothalamic magnocellular neurons of the rat. No immunoreactive met-enkephalin-Arg6-Gly7-Leu8, a fragment of the adrenal medulla pro-enkephalin molecule, was detected in magnocellular neurons. However, a strong met-enkephalin-Arg6-Gly7-Leu8-like immunostaining was seen in other regions of the brain. These results suggest that in magnocellular neurons dynorphin(1-8) exists independently from pro-enkephalin and therefore the magnocellular neurons represent a third opioid peptide neuronal system in brain. These observations, however, do not rule out a coexistence of proenkephalin and dynorphin-related peptides in other regions of the brain.     

Bioenergetic studies of mitochondrial oxidative phosphorylation using 31phosphorus NMR

The relationship between phosphorylation ratio [( ATP])/[ADP][Pi], phosphocreatine (PCr)/Pi, and ATPase activity was determined for isolated rat heart mitochondria, and the use of phosphorylation ratio and/or PCr/Pi as bioenergetic indices (Chance, B., Eleff, S., Leigh, J. S., Sokolow, D., and Sapega, A. (1981) Proc. Natl. Acad. Sci. U.S.A. 78, 6714-6718) was evaluated. Isolated rat heart mitochondria were suspended at low concentration (0.5-2.0 mg of protein/ ml) in oxygenated KCl/sucrose/4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid medium at 25 degrees C and pyruvate, malate, PCr, ATP, Pi, and Mg2+ were added. Changes in extramitochondrial phosphorus compounds were followed by 31P NMR. The ATPase activity was varied by the addition of potato apyrase. It was found that the logarithm of steady state PCr/Pi decreased linearly with increasing ATPase rate with a PCr/Pi intercept of 32.8 at 0 ATPase rate. The log phosphorylation ratio was also linearly related to the ATPase rate with an extrapolated maximum value of 6.87 at 0 ATPase rate, corresponding to a phosphorylation ratio of 7.41 X 10(6) M(-1) and a delta GATP of -16.3 kcal. The phosphorylation ratio in these experiments (for state 4 respiration) was greater by 1 or 2 orders of magnitude than previously reported for either isolated mitochondria or for whole tissue.     

Water transport in xylem conduits with ring thickenings

Helical or annular wall thickenings are not only present in protoxylem, but may also he a feature of the tracheids or vessel elements of secondary wood. The frequency of their occurrence tends to be a function of climatic factors and conduit diameter. In order to obtain a functional explanation for these structures, the hydrodynamic behaviour of xylem conduits with various patterns of annular wall thickenings was investigated numerically using a commercial CFD (Computational Fluid Dynamics) package. The fluid flow phenomena are presented in detail. The calculations show that the developing pressure gradient of the structures with corrugated walls is in each case lower than that of a smooth pipe with a diameter corresponding to the distance between two opposite thickenings. Furthermore, complex flow patterns with circulation zones between the thickenings develop which are dependent on the geometry of the wall. It may be hypothesized that these circulation zones influence the lateral water flow. The results are discussed with regard to the relationships between the water conduction function of the xylem and ecological factors.