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Well-maintained mitochondrial functioning is crucial for cellular physiology. Thus, multiple mechanisms are in place to preserve mitochondrial welfare upon homeostatic challenges. One such mechanism - known as protein quality control (PQC) - comprises a network of conserved proteases distributed across mitochondrial compartments. An emerging key PQC component is the ATP-independent metalloprotease Oma1, which has been identified as a key regulator of mitochondrial dynamics under normal and pathological states. Oma1 is activated by various stress stimuli - likely via conformational changes within the Oma1 homo-oligomeric complex. Here we provide evidence for the presence of a redox-dependent mechanism of Oma1 activation that appears to involve two conserved cysteine residues. First, we show that Oma1 oligomerization and protein stability are significantly impaired by the C332A mutation. Additional mutation of the conserved Cys-272 residue stabilizes the latter producing a functional Oma1 complex. However, this complex displays a lower activation threshold, likely due to altered conformational state. Second, the proteolytic activity of Oma1 is negatively regulated by the presence of thiol-containing reducing agents, but is not affected by non-thiol reductants. Consistently, proteolysis by the enzyme harboring both mutated cysteine residues displays lower sensitivity towards thioreduction. Lastly, the analyses in yeast model indicate that the Cys-272 and Cys-332 residues are in the oxidized state, which remains largely unchanged upon stress-activation. The human Oma1 appears to be following the same trend. Our data suggest a novel redox-sensitive mechanism for Oma1 activation and highlight an important role of the enzyme’s intermembrane space-exposed cysteines in this process.

Heme is an essential cofactor involved in a plethora of vital functions. Heme is required to be in most subcellular compartments, but the way, in which it is transported from the mitochondria - its site of synthesis - to those compartments is poorly understood. Utilizing ratiometric, fluorescent heme sensors, we found that the GTPases in control of mitochondrial fusion, Mgm1 and fission, Dnm1, are positive and negative regulators of heme trafficking to the nucleus, respectively. Furthermore, we discovered that mitochondrial network morphology is under the control of heme biosynthesis. Our results indicate that mitochondrial dynamics and heme trafficking are integrally coupled.

Objective Knowledge about the long-term course of spinal neuronal function after spinal cord injury (SCI) is important if regeneration therapies become available in the future. The objective of this study was to examine the behavior of locomotor EMG activity and of spinal reflexes in patients with chronic motor-complete SCI. Methods EMG activity from rectus femoris (RF), biceps femoris (BF), medial gastrocnemius (GM) and tibialis anterior (TA) of both sides was investigated during locomotor movements assisted by a robotic device in 10 chronic (>1 year after accident) complete SCI and 5 healthy subjects. H-reflexes (recorded from GM) were induced during the onset and flexion reflexes (recorded from BF and TA) at the end of the stance phase. Results Only in the chronic SCI subjects an exhaustion of EMG activity—i.e. a decrease in amplitude—occurred within a few minutes in all leg muscles. The EMG exhaustion was not associated with a change in the H- or flexion reflex amplitude during a walking session. Conclusions Exhaustion of neuronal function in chronic complete SCI might be restricted to unused motor tasks, i.e. locomotion. The fact that H- and flexion reflexes show a normal behavior might be due to the fact that they still become activated. Significance Training/pharmalogical approaches may be required to maintain neuronal function of unused tasks as a basis for future successful regeneration therapies.

An experimental setup to directly monitor the rates of light induced dry etching reactions is presented. We use an etching cell kept inside an ultrahigh vacuum chamber which allows in situ sample preparation and the combination with a vacuum ultraviolet monochromator for synchrotron radiation. The sample material is evaporated on a polished quartz crystal which serves to monitor the reaction rates via the frequency changes. As a model system measurements for Cu samples are presented with Cl2 as etching gas and Ar as carrier gas. We distinguish between processes originating from gas phase excitation (non-selective) and from surface excitation (selective). In addition the dark reaction is separated.

Introduction Using EMG and tension recordings during treadmill walking in spastic patients, the authors provide arguments that changes in mechanical muscle fibre properties contribute to spastic muscle hypertonia. Material and methods EMG activity and tension of the gastrocnemius and tibialis anterior muscles are registered in 15 hemiplegic patients during treadmill walking with and without disturbances. Results In the unaffected leg, tension and EMG activity were closely related. On the contrary, in the hemiplegic leg, the tension is increased throughout the stance phase while the EMG activity is depressed. When the foot is displaced backward, short and polysynaptic reflexes are presented in the unaffected leg while the polysynaptic reflexes are depressed in the hemiplegic leg. Discussion and conclusion The data suggest that the increased stretch reflexes are not the main mechanism responsible for the spastic movement disorder and that at least part of the impaired function is due to changes in mechanical muscle fibre properties.

The adaptation of leg movements to split-belt conditions was studied during treadmill walking in 10 healthy subjects. Four different belt speeds (0.5/1.0/1.5/2.0 m/s) were offered in all possible combinations for the left and right leg. All subjects automatically adapted to split-belt conditions. Although in all subjects and in all conditions the adaptation of leg movements within the stride cycle resulted in a walking pattern, the stepping pattern in conditions with extreme speed differences could be best described as limping. Regardless of the speed combination offered to the left and right leg, the adaptation to differences in left and right belt speed always involved: (1) Changes in stride cycle duration. The stride frequency in split-belt conditions was always intermediate to the values found during normal walking at speeds corresponding to the left and right belt speeds. There was a tendency towards the normal value of the faster belt, however. (2) An asymmetrical adaptation of the amplitude of leg movements. The support length of a leg generally tended towards the normal value for the speed offered to this leg. Thus, within the same cycle duration, the leg on the faster moving belt always made larger amplitudes than the slower leg. (3) An altered timing of support, swing and double support durations within the stride cycle. An increase in the relative duration of the support phase of the slower leg and the swing phase of the faster leg allowed for the larger amplitude of leg movements of the faster leg. Contrary to the asymmetric adaptation in support and swing durations the adaptation in the durations of both double support periods were more or less symmetric. The results of this split-belt walking study point to a high degree of flexibility in the relative timing of leg movements during walking. It is argued that the adaptation to split-belt conditions involves the tuning of low level coordinative mechanisms to the specific task requirements during split-belt walking by means of the afferent feedback resulting from the movement pattern.

Aluminum films of ∼ 5 μm thickness were deposited on oxidized Si wafers at T ≈ 260° C by UHV evaporation under simultaneous Kr or Xe bombardment. Normalized energies, En, ranged from 0 to 200 eV/at. mustructural characterization using X-ray diffraction, transmission electron muscopy, small-angle X-ray scattering and thermal desorption spectroscopy gave the following results: (1) Ion bombardment leads to a reduction of the grain size, especially near the film substrate interface by more than an order of magnitude. (2) For En ⩾ 80 eV/at. a { 111 } “single-crystal” texture develops with the crystals aligned to the ion beam direction. (3) For En ⩾ 30 eV/at. the gas content saturates at about 1 and 3 at.% for Xe and Kr, respectively. (4) The enclosed rare gas precipitates in a solid phase in small bubbles of ∼ 2 nm diameter. The resulting Xe and Kr crystals have fcc structure and are epitaxially aligned with the surrounding Al lattice. (5) In addition to the small bubbles there are but fewer large voids of a typical diameter of ∼ 10 nm. The evolution of film stress and grain size with En will be discussed in terms of gas incorporation and precipitation.

Ion bombardment during deposition enables the microstructure and properties of thin films to be manipulated in a controlled manner. Aluminium films approximately 5 μm thick were deposited on oxidized silicon wafers at T≈250 °C by ultrahigh vacuum electron beam evaporation. For normalized energies En in the range 0–200 eV (Al atom)-1 the influence of krypton and xenon ion bombardment during evaporation was investigated by X-ray diffraction, transmission electron microscopy, small angle X-ray scattering, scanning electron microscopy and thermal desorption spectroscopy. The results are discussed in terms of the change in texture, stress, grain size and content of gas bubbles. For 5 eV 40 eV the average rare gas content saturates at about 1 at.% and 3 at.% for xenon and krypton respectively. The gas precipitates within smaller bubbles as high-density f.c.c. solid epitaxially oriented with the aluminium. The distribution of bubbles is rather inhomogeneous even within individual grains.