Structure of thick filaments from insect flight muscle.

The supramolecular organization of thick (myosin) filaments isolated from insect flight muscle was studied using negative staining and shadowing techniques. The electron microscopical findings favour the two-stranded arrangement of double cross-bridges rather than a four- or six-stranded structures of single cross-bridges. The thick filament backbone consists of 12-subfilaments of myosin rods with a diameter of about 4 nm in agreement with the X-ray data.

How actin filament polarity affects crossbridge force in doubly-overlapped insect muscle.

We wished to find out why the internal resistance to shortening, which is negligible above rest length, becomes progressively more important with shortening below rest length. For this reason the movement of detached actin filaments in isometric sarcomeres treated with activating solution has been studied in insect flight muscle after breaking the filaments from the Z lines by stretching fibres in rigor. Evidence of sliding motion of such filaments has been produced by experimentally inducing double overlap zones in activating solution.

Cross-bridge interaction with oppositely polarized actin filaments in double-overlap zones of insect flight muscle.

An unresolved problem in understanding muscular contraction is why the internal resistance to sarcomere shortening increases progressively during contraction. We have addressed this problem here by investigating the movement of detached acting filaments in the sarcomeres of insect flight muscle. The final position of the detached actin filaments shows that they were able to slide freely into regions where they have the wrong polarity to interact actively with myosin (double-overlap zones) but where they prevent the exertion of force by cross-bridges between myosin and the correctly polarized acting filaments.

The continuity of thick filaments between sarcomeres in honey bee flight muscle.

One of the most frequently discussed problems of insect flight muscle morphology is the structure of the thick filaments, especially at the Z line. Many attempts have been to solve these problems but no unequivocal answers have been given so far. It is well known that physiological specialisation is accompanied by certain anatomical features in the myofibrillar level; the myofibrils have very short I bands in the resting state and the muscle acts under nearly isometric conditions.

X-ray microanalytical studies on native myofibrils and mitochondria isolated by microdissection from honey-bee flight muscle.

The distribution of elements was studied by means of energy dispersive X ray microanalysis in the honey-bee flight muscle. Semi-quantitative analysis of bulk muscle specimen, isolated mitochondria and isolated myofibrils either in resting or stretched state was performed. High K peak was observed in the spectra of bulk muscle specimen resembling the spectra of myofibrils and high P peak resembling the spectra of mitochondria.