The connective tissue of a lethal EDS IV case was investigated for the reasons of the manifested disturbances of the arterial wall. This functional disorder was attributed to the mechanical decoupling of elastin and collagen, with the premise of a composite material consisting of cellular, fibrillar, lamellar and other matrix components. A conceivable relation between the manifested deficiency of type III collagen and a disturbed anchoring of elastin is shown. These findings are supported by biochemical, morphological, x-ray and mechanical data.

Die Strukturdynamik von Sehnenfasern, d. h. die Ermittlung bestimmter Parameter an in Bewegung befindlichen Kollagenmolekülen, wird an nativen und an mit Hexamethylendiisocyanat (HMDI) künstlich vernetzten Sehnenfasern aufgezeigt. Das Ziel dieser Untersuchungen ist die analytische Erfassung und Lokalisation künstlich eingeführter Querbrücken mit Aussagewert für natürlicherweise vorkommende Vernetzungen. Voraussetzung hierfür ist der Einsatz neuer Technologien, so z. B. der Synchrotronstrahlung zur Erzeugung von Röntgenmeßdaten sehr schnell ablaufender dynamischer Vorgänge sowie die überraschende Tatsache, daß mit HMDI vernetzte Fasern ein von nativen Objekten nicht unterscheidbares Röntgendiagramm liefern.

The dynamic behaviour of collagen fibrils is revealed by time-resolved X-ray investigations of native rat tail tendon fibres in tensile tests.

The stretching of native fibres from rat tail tendons (RTT) was monitored in time-resolved X-ray measurements using synchotron radiation, by registering one meridional small angle diffraction pattern every second. The time course of this dynamic molecular process was analyzed quantitatively with the help of model calculations based on the amino acid sequence. The results show that two mechanisms contribute to the elongation of fibrils, namely the stretching of the collagen triple helices and their sliding relative to each other (increase of the D stagger). The results further show that these two processes do not take place simultaneously. The first increase of the D period from 67.0 nm to about 67.6 nm is correlated with a stretching of the triple helices. The further increase of the D period is due to a continuous increase of the D stagger. This succession is independent of the age of the animals and also independent of the stretching velocity. The stretching process is shown to be reversible at the molecular level up to a D period of about 68.4 nm.

Water has been found to be essential in the maintainance of collagen in its native conformation and is considered as an integral element of the collagen structure. The collagen triple helix differs from both the α-helix and the β-sheet structures in that not all hydrogen bonding sites on the backbone are occupied within the macromolecular structure. Only every third C=O and NH group of the backbone is involved in intramolecular hydrogen bonding. Water molecules stabilize the triple helical structure by intramolecular bridges by binding to the unoccupied hydrogen donor and acceptor groups on the protein backbone (Traub 1971; Ramachandran 1976).

X-ray diffraction analysis of connective tissue samples, which contain type I and type III collagen shows that twisted collagen fibrils are a general principle of assembly. The occurrence of twisted fibrils in native wet Chordae tendineae, skin and Aorta is combined with a shorter axial periodicity of about 65 nm. This shorter D period is shown to be directly related to the tilt of the molecules, which have to be curved to build-up twisted fibrils.

The differentiation between intermolecular and Interfibrillar cross‐linking has been achieved experimentally for collagen fibers for the first time. Decisive for this success was the use of a diisocyanate instead of dialdehydes to carry out the cross‐linking as well as the use of synchrotron radiation. The extent of intermolecular cross‐linking depends on the reaction time. These results should be applicable not only to collagen fibers but also to other fibrous biological polymers and high polymers whose structural dynamics can be studied by X‐ray diffraction analysis.

Small-angle x-ray diffraction spectra of dermatosparactic tendon collagen show a decreased intensity of the first order reflection. We interprete this finding to be due to the N-terminal propeptide which fills the intermolecular gap region partially.

Native collagen fibers were exposed to different dynamic loads to simulate damage to tendons and ligaments relevant clinically and for sports medicine. The results suggest that the rupture of a tendon is caused at the submicroscopic fibrillar level. Not only slow or very fast elongation, but also very fast unloading of stretched fibers seems to be responsible for disseminated damage, which reduces the stability of a fiber. This damage is induced by intrafibrillar sliding processes, which occur only a few seconds before macroscopic slippage takes place. The significance of these events for the beginning and progress of repair in vivo is discussed. The conclusions are supported by simultaneous mechanical and radiological measurements, as well as by light- and electron-microscopic results.

Small-angle x-ray diffraction spectra of dermatosparactic tendon collagen show a decreased intensity of the first order reflection. We interprete this finding to be due to the N-terminal propeptide which fills the intermolecular gap region partially.

Molecular rearrangements in native fibres of rat-tail tendons (RTT) and human finger flexor tendons are registered with the help of short time diffraction spectra using synchrotron radiation. There is a tension-induced increase of the 67 nm long period as well as changes in the intensities of some meridional small angle reflections (fig. 1). Both effects are reversible when unloading the fibre, but are preserved when the load is held constant until the fibre tears. The increase in the long period is due partly to an inhomogeneous molecular process as indicated by the change in the intensities and partly to a stretching of the triple helices themselves. The inhomogeneous behaviour is due to an increase of the D-stagger from 234 to for example 236 amino acid residues, caused by sliding of the triple helices relative to each other, which results in a change of the length of the gap and overlap regions. This sliding of triple helices which are aligned according to the scheme of Hodge and Petruska is coupled with a stretching of the cross-linked telopeptides. This interpretation is supported by calculated axial electron density distributions under consideration of the relative intensities derived from models with varying length of gap and overlap regions, as well as by comparison with model calculations which include telopeptides.

Tension-induced molecular rearrangements in wet native fibres of rat-tail tendons and human finger flexor tendons are registered with the help of time-resolved diffraction spectra using synchrotron radiation. The tension-induced increase of the 67 nm D period is combined with changes in the intensities of some orders of the meridional small angle reflection. Both effects are reversible when unloading the fibre, but are preserved when the load is held constant until the fibre tears. The increase in the D period is partly due to a sliding of the triple helices relative to each other and partly due to a stretching of the triple helices themselves. The sliding of the triple helices results in an alteration of the D stagger, leading to a change in the length of the gap and overlap regions, and to a stretching of the cross-linked telopeptides. This interpretation is supported by comparison with the relative intensities derived from a model with varying length of gap and overlap regions, as well as by comparison with model calculations that include the telopeptides.

X-ray diffraction data of collagen molecules modified with 2-propanol favour a quasi-hexagonal lateral packing over a quasi-tetragonal one.

The exchange of the structural water of collagen for alcanols was investigated using X -ray diffraction combined with mechanical measurements. The stepwise dehydration with methanol, ethanol or 1-propanol is reflected by the reversible loss of the characteristic equatorial reflexions of native rat tail tendons. The exchange for 1-alcanols in ascending homologous order is characterized by: 1. an increase in the distance between the axes of the triple helices depending on the number of carbon atoms of the alkyl chain, 2. a shortening of the long-spacing of 67 nm characteristic of native collagen and 3. the herewith correlated increase in tension on isometrically measured fibres. The stepwise dehydration with 2-propanol leads first to a loss of the equatorial reflexions that are characteristic of native collagen, then to their reappearance at smaller diffraction angles. The exchange for 2-alcanols in ascending homologous order is characterized by: 1. a splitted equatorial reflexion at 4.1 ± 0 .1 nm, that stays constant up to 2-nonanol, and moves to 4 .8 - 5 .0 ± 0 .1 nm with more than 9 carbon atoms in the alkyl chain, 2. a shortening of the long spacing of 67 nm characteristic of native collagen and 3. the herewith correlated increase in tension on isometrically measured fibres. Stereochemical requirements are discussed as well as consequences for the structural model of collagen.

Mechanochemically induced molecular transformations of collagen fibres were analysed using time-resolved small-angle diffraction spectra and histomechanical measurements. In particular, the influence of aqueous and methanolic perchlorate solutions was examined. According to a transformation continuing from the periphery towards the centre, the macroscopic contraction that is completed less than five minutes after incubation with perchlorate is caused by peripherally transformed fibrils only, whereas the centrally situated fibrils first undergo an accordion-like folding, but after more than 20 minutes are transformed similarly. The triple-helical transformation is preceded by a structure-breaking effect on structural water that can be monitored in time-resolved diffraction spectra. The combined loss of meridional low-angle reflections and cross-striated fibrils in micrographs is irreversible. By dialysis of colloidally dissolved collagen against a solution of ATP, however, segment-long spacing aggregates are obtained. Under isometric conditions, an instantaneous transformation of intermittent regions leads to an increase in the long period of adjacent, still structured regions of the same fibril that is correlated with a delayed increase intension in the fibre. Increase of tension under isometric conditions as well as the flow-properties of a fibre relaxed in perchlorate are interpreted in terms of the parallel sliding of subunits of varying lengths, which has been demonstrated by diffraction analysis.