Showing papers by "University of Konstanz published in 1968"

Binding of glycolytic enzymes to structure proteins of the muscle.

Abstract: 1 Only 60–70% of the total activity of aldolase can be extracted from rat or rabbit muscle homogenates with aqueous solutions of relatively low ionic strength. The extraction of aldolase from muscle tissue is only complete in aqueous solutions with an ionic strength greater than 0.2. The fraction of aldolase which is set free at high ionic strength is not located within a special cellular compartment but is present in a bound form and is desorbed in dependence of the ionic strength of the extraction medium. 2 F-actin, myosin, acto-myosin and stroma-protein were prepared from rabbit muscle and the binding of aldolase to each of these structure proteins was studied in vitro. A completely reversible binding of aldolase to F-actin, actomyosin, myosin and stroma protein was found. F-actin possesses by far the highest binding capacity. 100% of the enzyme is bound when 1 mg of aldolase is added to 1 mg of highly purified F-actin. Under identical experimental conditions acto-myosin binds 40%, myosin 25%, and stroma protein only 15% of the aldolase activity. 3 A modified Langmuir isotherm is derived, and the analytical evaluation supports the assumption that the binding of aldolase to F-actin occurs at two different binding sites. 4 The binding of aldolase to F-actin and other structure proteins depends on the ionic strength. At 150 mM KCl, a complete desorption occurs, and 50% of the actin-bound aldolase is set free at a concentration of 80 mM KCl. The sigmoid shape of the desorption curve indicates a cooperative mechanism of the binding phenomenon. 5 Within the physiological range, the pH does not influence the binding of aldolase to F-actin. 6 Similar to aldolase, glyceraldehydephosphate dehydrogenase is bound to F-actin, and under the experimental conditions, 1 mg of F-actin binds up to 1.2 mg of glyceraldehydephosphate dehydrogenase. 7 Studies with a purified preparation of myogen reveal that also fructose-6-phosphate kinase, and in a lower degree phosphoglycerate kinase, pyruvate kinase and lactate dehydrogenase can be adsorbed to F-actin. No binding occurs in the case of creatine kinase. 8 The possible significance of the binding phenomenon is discussed with respect to the location of the Embden-Meyerhof system at the site of the actin filaments within the isotropic zones of the cross-striated muscle fiber.

An electron microscopical study of spider muscles

Abstract: Die Pasern aus den Beinmuskeln der Vogelspinne Dugesiella hentzi sind zwischen 100 und 250 μm dick und durch tiefe Einfaltungen des Sarcolemms in Untereinheiten gegliedert. Die meist bandformigen Myofibrillen liegen darin in radiarer Anordnung. A-Bandbreite und Sarcomerenlange variieren sehr stark (Extremwerte 2,8 und 5,6 bzw. 3,0 und 7,3 μm). Ausrichtung und Anordnung der Myofilamente sind wenig exakt. Auf ein Primarfilament (Durchmesser 230–235 A) kommen durchschnittlich 4–4,5 Sekundarfilamente (70–80 A). Das sarcoplasmatische Reticulum (SR) ist extensiv und in Form eines unregelmasigen Netzes aus schlauchartigen Elementen ausgebildet. Im Bereich des A-Bandes erweitern sich einzelne Schlauche zu Cisternen, die mit den Tubuli des Transversalsystems Dyaden bilden. Die SR-Membran zeigt dabei im Dyadenbereich charakteristische Strukturen: punktformige Membranverdickungen, die ein Muster von groser Regelmasigkeit bilden. Lage und Zahl der Dyaden sind sehr variabel (Durchschnitt 3–4 pro Sarcomer).

Free radicals of biological interest as studied by electron spin resonance

Abstract: Electron spin resonance has become a major tool for investigating biological one-electron or radical group transfer. The scope and limitations of this method are considered and emphasis is placed on the first of the following two questions that govern the field: (1) What is the structure, stability and potential biological function of radicals that might occur as biological intermediates? (2) Which radicals have been demonstrated up to now as ( a ) occurring in biological reactions, ( b ) being essential biological intermediates? The two questions deserve independent consideration and supplement each other. However, the second question can hardly be decided before the first one, though there may be a severe temptation to claim the occurrence or even stabilization of a certain radical without any structural evidence. Among the free radicals considered here are phenoxyls, mercaptyls, semidiones, (aza)semi-quinones (from flavins and pteridines), and metal-stabilized radicals.

Aktivierung von Sauerstoff in Modellsystemen

Abstract: Eine direkte Untersuchung der Reaktionen des Sauerstoffmolekuls stost auf erhebliche Schwierigkeiten, die vor allem durch die relativ komplizierte elektronische Struktur und die hohe Reaktionsgeschwindigkeit des Sauerstoffs und seiner verschiedenen Reduktionsstufen begrundet sind. Es hat deshalb nicht an Versuchen gefehlt, die Biochemie des Sauerstoffs mit Hilfe von Modellreaktionen aufzuklaren. Vor allem das Problem der „Aktivierung des Sauerstoffs“durch Enzyme ist schon sehr fruh diskutiert worden und Gegenstand vieler Arbeiten von Traube [1], Engler [2], Bach [3], Wieland [4] und Warburg [5]. Die neueren Untersuchungen zu dem Thema Sauerstoffaktivierung sind so zahlreich, das hier nur Modellreaktionen fur diejenigen Enzyme besprochen werden sollen, bei denen die Bildung eines aktiven Sauerstoffs nachgewiesen ist oder postuliert werden mus. Das trifft praktisch nur fur die Oxy-genasen zu und schliest die Oxidasen und sauerstofftransportierenden Enzyme aus, bei denen gerade keine aktiven Formen des Sauerstoffs gefunden wurden und fur den Enzymmechanismus auch nicht benotigt werden.