Phase transition kinetics of phosphatidic acid bilayers A stopped-flow study of the electrostatically induced transition

The kinetics of the electrostatically induced phase transition of dimyristoyl phosphatidic acid bilayers was followed using the stopped-flow technique. The phase transition was triggered by a fast change in the pH or the magnesium ion concentration and followed by recording the time dependence of the absorbance. When the phase transition was induced by a pH jump the time course of the absorbance could be described by two exponentials, their time constants displaying the for cooperative processes characteristic maximum at the transition midpoint. The time constants are in the 10 and 100 ms range for the H⁺ triggered transition from the fluid to the ordered state. A third slower process shows no appreciable temperature dependence and is probably caused by vesicle aggregation. For the OH^--induced transition fron the ordered to the fluid state the time constants are in the 100 and 1000 ms range. The fluid-ordered transition could also be triggered by addition of magnesium ions. Of the several observed processes only the fastest in the 10–100 ms time range could definitely be assigned to the fluid-ordered transition while the others are due to aggregation phenomena. The experimental data were compared with results obtained from pressure jump experiments and could be interpreted on the basis of theories for non-equilibrium relaxation.     

A spectrophotometric method for determining the stream sample core diameter of a flow cytometer

A simple, rapid, and accurate method is described for the determination of flow cytometer stream sample core diameters. A precisely formulated solution of potassium dichromate is introduced as a sample, the stream is collected, and its absorbance is measured using a spectrophotometer. This permits the calculation of the factor by which the original solution was diluted and, given the stream diameter, the sample core diameter.     

Dictyostelium discoideum gene family contains a long internal amino acid repeat

Two different cDNA clones denoted pTO270-6 and pTO270-11 represent two mRNAs that are developmentally regulated during spore germination in Dictyostelium discoideum. The respective mRNAs are found only during early germination and are not present in other stages of growth or multicellular development. Four different genomic clones that hybridize to sequences that are common to both of the 270 cDNA clones were isolated from Dictyostelium libraries and sequenced. Two are the genes for the two cDNAs, and the other two represent genes that do not seem to be transcribed. All four genomic sequences possess a very unusual internal feature in the deduced protein sequences composed of a monotonous repeat of the tetrapeptide threonine-glutamic acid-threonine-proline. The other portions of the proteins have no homology among themselves. The deduced protein corresponding to the 270-6 gene is very similar to avocado (Persea americana) cellulase. Since cellulose in the spore wall has to be digested during spore germination this suggests that this protein may function as an endo-(1,4)-beta-D-glucanase during germination.     

Isolation of a cDNA clone for the alpha subunit of the human GABA-A receptor

A cDNA clone of an alpha subunit of the human GABA-A receptor has been isolated. The human clone (pCLL800) contains 1055 nucleotides in an open reading frame and 260 nucleotides in the 5' non-coding region. The 351 amino acid sequence of this human alpha subunit shows 97% homology with its bovine counterpart. Hybridization of pCLL800 to Northern blots shows a 3.9/4.3 Kb RNA doublet in human cortex, rat whole brain, cortex, hippocampus, midbrain, olfactory bulb and cerebellum. Developmental studies show that the levels of the rat alpha mRNA increase between one and three weeks of age in a manner similar to the development of the benzodiazepine binding sites.     

Schriftenschau

Ohne Zusammenfassung     

Beitrag zur Populationsgenetik der Pyruvatkinase menschlicher Erythrocyten

Summary In 214 healthy young Germans the activity of Pyruvatekinase from red blood cells has been determined. Three persons had values in the heterozygote range between 10.0 and 20.0 U. Suggesting a 2-allele-model the frequency of the three phenotypes in the German population can be calculated as followed: PK(A)=98.6%, PK(AB)=1.4%, PK(B)=0.005%.No correlation could be found between the distribution of blood-and serum-groups and the enzyme-activity.

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Direktor: Prof. Dr. med. G. W. Löhr

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Direktor: Prof. Dr. med. G. G. Wendt

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Mit dankenswerter Unterstützung durch die Deutsche Volkswagen-Stiftung.

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Herrn Professor Dr.H. E. Bock, Tübingen, zum 65. Geburtstag gewidmet. Wesentliche Teile dieser Arbeit werden von Olaf Praetsch der Medizinischen Fakultät als Dissertation vorgelegt.     

Studies on isoniazid conversion in Thailand

Isoniazid inactivation was studied in a sample of 100 subjects from Central Thailand. The frequency of the allele Ac^S (resulting in slow inactivation in the homozygous state) was calculated as 0.755. There is evidence for a simply additive dosage effect of the two genes Ac^R and Ac^S. The results are discussed with regard to other population studies and to recent findings concerning isoniazid inactivation and the activity of the involved enzymes in nonhuman primates.     

Evidence for RNA-Oligonucleotides in Plant Vacuoles Isolated from Cultured Tomato Cells

We have shown that highly purified vacuoles of suspension-cultured tomato (Lycopersicon esculentum) cells contain RNA-oligonucleotides, using two different approaches to label and detect RNA: (a) in vivo labeling of cellular RNA with [5-³H]uridine, followed by preparation of vacuoles from protoplasts and by quantification of radioactively labeled material; and (b) in vitro labeling and analysis on sequencing gels of nucleic acids prepared from tomato vacuoles and their identification as RNA. The intravacuolar location of the RNA found in vacuolar preparations was concluded from analyzing for RNA intact organelles after repeated flotation steps as well as ribonuclease A treatment. About 3% of the RNA in protoplasts was localized within vacuoles, exceeding by severalfold the contribution made by contamination with unlysed protoplasts and subcellular organelles. Investigation of the size distribution of vacuolar RNA revealed an oligonucleotide pattern strikingly different from that which would arise from contaminating protoplasts; vacuolar RNA fragments are considerably shorter than 80 nucleotides. Characterization of these oligoribonucleotides (3′-phosphorylated termini; relatively rich in pyrimidines) as possible products of tomato vacuolar ribonuclease I action, and, in addition, enzymatic hydrolysis of vacuolar RNA by inherent enzyme activities in lysed vacuole preparations support the hypothesis that plant vacuoles are involved in cellular nucleolytic processes.