Strukturanalytische Untersuchungen zur Altersabhängigkeit der Sensibilität

Zusammenfassung Eine Analyse der Meßwerte von Ronge (1943) über die Reizausnutzung durch das Tastsinnes-Nervensystem der Haut zeigt im Zusammenhang mit einer vorausgegangenen Studie (Scharf und Blumenthal, 1967), daß der Reizerfolg in einer transzendenten Fläche höherer Ordnung in Abhängigkeit vom Lebensalter (oder von der Anzahl der Meissnerschen Tastkörperchen pro Hautflächeneinheit) und vom Reizdruck dargestellt werden kann. In Druckrichtung steigt diese Fläche mit zunehmendem Reizdruck nichtlinear an, in Zeitrichtung oscilliert die Fläche dagegen träge um Normwerte, die beim 20jährigen Menschen realisiert sind. Dabei werden die Altersveränderungen der histologischen Hautstruktur offenbar zur Kompensation der altersabhängigen Verminderungen der Zahl der Tastkörperchen ausgenutzt.

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Summary An analysis of the observations on the Reizausnutzung by nerves of touch (Ronge, 1943) connected to a previous study (Scharf and Blumenthal, 1967) shows that the irritation result may be figured by a transcendental plane of higher order as a function of age (or number of Meissner's corpuscles per area skin) and irritation pressure. Along the pressure axis this non-linear plane is increasing non-linear in dependence on ascending pressure, but along the time axis the plane oscillates lazily round about the norm values which are realized in human beings of about 20 years of age. It seems that the age-dependent changes of histological skin structure are utilized to compensate the age-dependent diminution of touch corpuscle number.

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Mit dankenswerter Unterstützung durch einen Forschungsauftrag des Staatssekretariates für das Hochschulwesen der DDR.

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Numerische Rechnung: Tischrechner Mercedes Cellatron R 44 SM, Leitende Med. techn. Ass. Ruth Pieper (Anatomisches Institut Halle). Programmgesteuerter Digitalrechner ZRA 1, Math, techn. Ass. Friedegund Hüther (Institut für Numerische Mathematik, Halle).

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Graphik: Akad. Bildhauer Hellmut Helwin.     

A study of correlates of hand preferences in squirrel monkeys (Saimiri sciureus)

The purpose of this study was to test the influence of sex, age, social rank, matriline membership, posture, and visual and tactual motor control on manual preferences inSaimiri sciureus. A well-established social group of 12 squirrel monkeys, aged 2 to 14 yrs and consisting of two matrilines with social rank known for each animal, was presented with four different food-reaching tasks and assessed for hand preferences with a minimum of 100 reaches per animal. Frequency of occurrence of hand preferences at the group level and degree of hand preferences at the individual level depended on posture and on whether the reaching act took place under visual or tactual guidance. Sex, age, social rank, and matriline membership were not found to determine frequency of occurrence, direction or degree of hand preferences with the exception of one task in which a significant negative correlation between the degree of hand preference and age was found. Nine out of 12 monkeys showed task-dependent changes in the hand they used preferentially while only three animals preferred the same hand in all four tasks. Significant preferences for the use of right or left hand on a given task were distributed almost equally between individuals. Thus, the results of this study suggest task-specific demands like posture and/or whether reaching was visually or tactually guided to be the major correlates of hand preferences in food-reaching tasks in squirrel monkeys.     

Synthetic substrate analogues for UDP-GlcNAc: Manα1-6R β(1-2)-N-acetylglucosaminyltransferase II. Substrate specificity and inhibitors for the enzyme

UDP-GlcNAc: Man1-6R (1-2)-N-acetylglucosaminyltransferase II (GlcNAc-T II; EC 2.4.1.143) is a key enzyme in the synthesis of complexN-glycans. We have tested a series of synthetic analogues of the substrate Man1-6(GlcNAc1-2Man1-3)Man-O-octyl as substrates and inhibitors for rat liver GlcNAc-T II. The enzyme attachesN-acetylglucosamine in 1-2 linkage to the 2-OH of the Man1-6 residue. The 2-deoxy analogue is a competitive inhibitor (K _i=0.13mm). The 2-O-methyl compound does not bind to the enzyme presumably due to steric hindrance. The 3-, 4- and 6-OH groups are not essential for binding or catalysis since the 3-, 4- and 6-deoxy and -O-methyl derivatives are all good substrates. Increasing the size of the substituent at the 3-position to pentyl and substituted pentyl groups causes competitive inhibition (K _i=1.0–2.5mm). We have taken advantage of this effect to synthesize two potentially irreversible GlcNAc-T II inhibitors containing a photolabile 3-O-(4,4-azo)pentyl group and a 3-O-(5-iodoacetamido)pentyl group respectively. The data indicate that none of the hydroxyls of the Man1-6 residue are essential for binding although the 2- and 3-OH face the catalytic site of the enzyme. The 4-OH group of the Man-O-octyl residue is not essential for binding or catalysis since the 4-deoxy derivative is a good substrate; the 4-O-methyl derivative does not bind. This contrasts with GlcNAc-T I which cannot bind to the 4-deoxy-Man- substrate analogue. The data are compatible with our previous observations that a bisectingN-acetylglucosamine at the 4-OH position prevents both GlcNAc-T I and GlcNAc-T II catalysis. However, in the case of GlcNAc-T II, the bisectingN-acetylglucosamine prevents binding due to steric hindrance rather than to removal of an essential OH group. The 3-OH of the Man1-3 is an essential group for GlcNAc-T II since the 3-deoxy derivative does not bind to the enzyme. The trisaccharide GlcNAc1-2Man1-3Man-O-octyl is a good inhibitor (K _i=0.9mm). The above data together with previous studies indicate that binding of the GlcNAc1-2Man1-3Man- arm of the branched substrate to the enzyme is essential for catalysis. Abbreviations: GlcNAc-T I, UDP-GlcNAc:Man1-3R (1-2)-N-acetylglucosaminyltransferase I (EC 2.4.1.101); GlcNAc-T II, UDP-GlcNAc:Man1-6R (1-2)-N-acetylglucosaminyltransferase II (EC 2.4.1.143); MES, 2-(N-morpholino)ethane sulfonic acid monohydrate.     

The influence of the cytosolic oncotic pressure on the permeability of the mitochondrial outer membrane for ADP: implications for the kinetic properties of mitochondrial creatine kinase and for ADP channelling into the intermembrane space

Summary Cytosolic proteins as components of the physiological mitochondrial environment were substituted by dextrans added to media normally used for incubation of isolated mitochondria. Under these conditions the volume of the intermembrane space decreases and the contact sites between the both mitochondrial membranes increase drastically. These morphological changes are accompanied by a reduced permeability of the mitochondrial outer compartment for adenine nucleotides as it was shown by extensive kinetic studies of mitochondrial enzymes (oxidative phosphorylation, mi-creatine kinase, mi-adenylate kinase). The decreased permeability of the mitochondrial outer membrane causes increased rate dependent concentration gradients in the micromolar range for adenine nucleotides between the intermembrane space and the extramitochondrial space. Although all metabolites crossing the outer membrane exhibit the same concentration gradients, considerable compartmentations are detectable for ADP only due to its low extramitochondrial concentration. The consequences of ADP-compartmentation in the mitochondrial intermembrane space for ADP-channelling into the mitochondria are discussed.     

Electron microscopic structural analysis of Photosystem I,Photosystem II,and the cytochromeb6/f complex from green plants and cyanobacteria

Electron microscopy (EM) in combination with image analysis is a powerful technique to study protein structure at low- and high resolution. Since electron micrographs of biological objects are very noisy, substantial improvement of image quality can be obtained by averaging individual projections. Crystallographic and noncrystallographic averaging methods are available and have been applied to study projections of the large protein complexes embedded in photosynthetic membranes from cyanobacteria and higher plants. Results of EM on monomeric and trimeric Photosystem I complexes, on monomeric and dimeric Photosystem II complexes, and on the monomeric cytochromeb6/f complex are discussed.     

Cloning and molecular analysis of the poly(3-hydroxybutyric acid) biosynthetic genes of Thiocystis violacea

From a genomic library of Thiocystis violaceae strain 2311 in L47, two adjacent EcoRI restriction fragments of 5361 base pairs (bp) and of 1978 bp were cloned. The 5361-bp EcoRI restriction fragment hybridized with a DNA fragment harbouring the Alcaligenes eutrophus poly(3-hydroxyalkanoate) (PHA) synthase operon (phbCAB) and restored the ability to synthesize and accumulate PHA in PHA-negative mutants derived from A. eutrophus. The nucleotide sequence analysis of both fragments revealed five open-reading frames (ORFs); at least three of them are probably relevant for PHA biosynthesis. The amino acid sequences of the putative proteins deduced from these genes indicate that they encode a -ketothiolase [phbA _Tv, relative molecular mass (M_r) 40850], which exhibited 87.3% amino acid identify with the -ketothiolase from Chromatium vinosum. The amino acid sequences of the putative proteins deduced from ORF2_Tv (M_r 41 450) and phbC _Tv (M_r 39 550), which were located upstream of and antilinear to phbA _Tv, exhibited 74.7% and 87.6% amino acid identify, respectively, with the corresponding gene products of C. vinosum. Downstream of and antilinear to phbC _Tv was located ORF5, which encodes for a protein of high relative molecular mass (M_r 76428) of unknown function. With respect to the divergent organisation of ORF2_Tv and phbC _Tv on one side and of phbA _Tv on the other side and from the homologies of the putative gene products, this region of the T. violaceae genome resembled very much the corresponding region of C. vinosum, which was identified recently. Correspondence to: A. Steinbüchel