Correlated Diffusion of Membrane Proteins and Their Effect on Membrane Viscosity

We extend the Saffman theory of membrane hydrodynamics to account for the correlated motion of membrane proteins, along with the effect of protein concentration on that correlation and on the response of the membrane to stresses. Expressions for the coupling diffusion coefficients of protein pairs and their concentration dependence are derived in the limit of small protein size relative to the interprotein separation. The additional role of membrane viscosity as determining the characteristic length scale for membrane response leads to unusual concentration effects at large separation—the transverse coupling increases with protein concentration, whereas the longitudinal one becomes concentration-independent.     

Zur Kenntnis kritischer Wasser-Sättigungsdefizite in Blättern und Ihrer Bestimmung

Zusammenfassung Das subletale Wasser-Sättigungsdefizit welkender Blätter, von dem Verfasser früher durch das Auftreten nekrotischer Flecken definiert, zeigt ein fortgeschrittenes Stadium von Schädigung an. Sehr oft vertrocknen Blätter, ohne daß solche in Erscheinung treten. Versuche mit immergrünen Sträuchern und Bäumen des Mittelmeergebiets führten zu der Erkenntnis, daß ernstlicher Schaden in abgetrennten Blättern einsetzt, wenn etwa 35% des Sättigungswassergehaltes verausgabt worden sind. Bei geringerer Entwässerung wird der ursprüngliche Wassergehalt nach Einfrischung ungefähr wieder erreicht. Jenseits des permanenten Turgor-Verlust-Punktes (PTLP) steigt die Zahl geschädigter Zellen ständig an, und es entwickelt sich so ein Wasser-Rücksättigungs-Defizit (WRD), das mehr oder weniger linear mit dem weiteren Wasserverlust anwächst. Zunehmender Gewebe- und Zellschaden konnte in diesem Stadium der Entwässerung durch Vitalitätsprüfungen nachgewiesen werden.Schädigungen und Tod durch Trockenheit sind ein langdauernder und allmählicher Vorgang, ähnlich wie bei Strahlungs- und Hitzeschäden. Sie beruhen anscheinend auf Eiweißdenaturierung, die, anfangs umkehrbar, schließlich tödlich wirkt.Verbreitete Ansichten über die Menge des ohne Schaden verfügbaren Wassers müssen abgeändert werden. Jedoch ist zuzugeben, daß an der Pflanze Blätter vielleicht höhere Wasserverluste ertragen als nach ihrer Abtrennung.Der Verfasser weiß sich Herrn Dr.B. Jacoby, FrauRuth Arbel und FrauAdiva Shomer-Ilan für ihre Hilfe bei der Durchführung der Versuche zu Dank verpflichtet.

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Summary The sublethal water saturation deficit in wilting leaves earlier defined by the author through the appearance of necrotic spots, indicates a progressive state of damage. Quite often leaves dry up without formation of any spots. Experiments with leaves of Mediterranean evergreen trees and shrubs led to the conclusion that serious damage in detached leaves sets in when about 35% of the water content at saturation has been spent. Less wilted leaves approximately regain their initial weight in rehydration. Beyond the permanent turgor loss point (PTLP) the number of damaged cells increases steadily producing an increasing water resaturation deficit which is more or less linearly related to water loss beyond the PTLP. Increasing damage to tissues and cells could be demonstrated by vitality tests in this phase of dehydration.Damage and death produced by drought is a prolonged and gradual process, in analogy to phenomena produced by radiation and heat. It is apparently produced by protein denaturation which, reversible in an early stage, becomes fatal, later on.Current views on available water in wilting leaves must be revised. However, the possibility that on the plant leaves may be able to suffer larger water losses than in the detached condition, is admitted.

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Herrn Prof.A. Pisek zum 70. Geburtstage gewidmet.     

Quantitative agglutination of specific populations of sea urchin embryo cells with concanavalin A

It has been demonstrated that specific changes in carbohydrate-containing cell surface lectin receptor sites occur with differentiation and maturation of sea urchin embryo cells. In this study, evidence is presented, using a quantitative electronic particle counter assay to measure agglutination, which indicates that concanavalin A (Con A) mediated agglutination of dissociated 32/64 cell sea urchin embryos differs dramatically with respect to specific cell populations. The migratory cell type, the micromere, is significantly more agglutinable with Con A than the other cell types and colchicine treatment markedly increases sea urchin embryo cell agglutinability. The results indicate that like many malignant cells which display extensive migratory behavior, specific migratory populations of embryonic cells are agglutinable with Con A. The results are discussed with respect to the possible nature of lectin receptor sites on specific populations of embryonic cells and the possible role of colchicine-sensitive structures in controlling the display patterns of these sites.     

Cell density-dependent stimulation of glutamine synthetase activity in cultured mouse teratoma cells

A density dependent stimulation of glutamine synthetase (GS) activity has been observed in cultures of mouse teratoma cells. GS specific activity increased as cultures approached confluency to a level greater than 2-fold over the basal level found in sparse cultures. After confluency the GS specific activity returned to the basal level found in sparse cultures. The enzyme increase could not be attributed to age of cultures, medium or glutamine depletion, cell leakage of GS, or change in the amount of cellular protein. Dibutyryl cyclic AMP (db-cAMP) plus theophylline lowered GS specific activity both in cultured teratoma and in teratoma obtained from ascites grown tumors. The enzyme increase observed in cultured teratoma cells could be prevented by cycloheximide, and enhanced by hydrocortisone or actinomycin D.     

Two-dimensional 1H NMR of three spin-labeled derivatives of bovine pancreatic trypsin inhibitor

Three nitroxide spin-labeled monoderivatives of bovine pancreatic trypsin inhibitor were prepared with the amino-specific reagent succinimidyl 1-oxy-2,2,5,5-tetramethyl-3-pyrroline-3-carboxylate. The monoderivatives were purified by ion-exchange and affinity chromatography. Thin-layer maps of tryptic peptides of the monoderivatives showed that the spin-label was incorporated at either the alpha-amino group, Lys-15, or Lys-26. Two-dimensional J-correlated 1H NMR spectra of the monoderivatives were recorded. Spectra were also recorded after reduction by ascorbic acid of the nitroxide label to hydroxylamine. With the nitroxide label present, significant line-broadening effects on many of the cross peaks in the spectra were observed. The extent of line broadening for the C alpha H-NH cross peaks was qualitatively correlated with the distance between the labeled amino group and the average C alpha H-NH position in the crystal structure. The spin-label affects cross peaks of protons within approximately 15 A. This study suggests that it is feasible to accumulate sufficient intramolecular distances in order to determine protein solution structures with the aid of distance geometry algorithms.     

A myb gene required for leaf trichome differentiation in Arabidopsis is expressed in stipules

The GL1 gene is required for the initiation of differentiation of hair cells (trichomes) on the crucifer, Arabidopsis thaliana. This gene has been localized to a 4.5 kb DNA fragment by molecular complementation of gl1 mutants. DNA sequence analysis has shown that the protein encoded by GL1 contains a Myb DNA-binding motif. Southern analysis and subsequence analysis of isolated lambda clones has established that GL1 is a member of an extensive myb gene family in Arabidopsis. The putative GL1 promoter directs the expression of the GUS reporter gene in non-trichome-bearing structures that appear to be stipules. This pattern of expression suggests that GL1 may control the synthesis of a diffusible signal that activates the developmental pathway for trichome differentiation.