PMID: 6540038Jan 1, 1984Paper

A-band mass exceeds mass of its filament components by 30-45%

Advances in Experimental Medicine and Biology
Mary C Reedy, C Lucaveche

Abstract

We have measured filament lattice spacing in fibrils using X-ray diffraction, and find that STEM-determined mass/length values reported for myofilaments should give 13% w/v as the filament protein concentration in the lattice of the AO-band (filament overlap zone) of both insect flight muscle (IFM) and vertebrate skeletal muscle ( VSkM ). This is well below the actual mass concentration of AO-bands as measured by immersion refractometry of detergent-washed rigor myofibrils under the phase microscope. This technique identifies an immersion fluid of suitable refractive index (RI) for matching out all image contrast between background and the selected cross-band. We used RI fluids in which the effective RI matching component is a large-particle solute (Percoll or hemocyanin) excluded by the filament lattice. The measured RI indicates that protein concentration in AO-bands is 16-17% in Lethocerus and other IFM fibrils including CAF-digested fibrils, and is 18-19% in rabbit VSkM fibrils. On IFM fibrils we also measured absolute buoyant density in Percoll as greater than or equal to 1.042; this supports the value for mass concentration as determined by RI. The mass discrepancy between fibrils and filaments does not seem to arise from...Continue Reading

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