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Ionic strength and myofibrillar protein solubilization
Abstract:
Myofibrils from bovine longissimus muscle were obtained at 2 h postmortem and incubated in .10 to .35 M ionic strength buffers under various conditions in vitro. Increasing ionic strength or increasing the incubation time from 1 to 72 h decreased the turbidity of suspensions of myofibrils and increased myofibrillar solubilization (P less than .01 for both measures). The use of KCl or NaCl to elevate ionic strength gave essentially identical results, but lactate generally was ineffective in changing either the percentage myofibrillar solubilization or the turbidity of suspensions of myofibrils. Gel electrophoresis under denaturing conditions indicated that KCl was more effective than NaCl in causing the release of C-protein from myofibrils, and both salts were quite effective in dissociating M-protein, actin, troponin-T, tropomyosin, myosin light chain-3 and a 30,000-dalton molecular weight protein from myofilaments. Small increases in alpha-actinin also were observed, especially in samples incubated for 72 h. Substantially more myosin light chain-3, tropomyosin (or paratropomyosin) and troponin-T, and less actin and the 30,000-dalton protein, were released in samples incubated at pH 5.5 than at pH 7.0 (P less than .05). Electron micrographs indicated loss of thick filament ultrastructure after incubation for 24 h in either .1 or .3 M ionic strength, but the Z-lines were largely unaffected. In samples that had first been incubated with trypsin for 10 min, the Z-lines were virtually indistinguishable at .1 M ionic strength, and absolutely no myofibrillar structures could be discerned in samples incubated in .3 M ionic strength buffer.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
High ionic strength and extended incubation solubilize bovine myofibrils, releasing key proteins like actin and myosin. pH 5.5 further impacts protein release and myofibril structure.
Area of Science:
- Meat Science
- Protein Biochemistry
- Muscle Biology
Background:
- Myofibrils are the primary contractile units in muscle tissue.
- Understanding myofibrillar protein behavior is crucial for meat quality and processing.
Purpose of the Study:
- To investigate the effects of ionic strength, incubation time, and pH on bovine myofibril structure and protein solubility.
- To identify specific myofibrillar proteins affected by these in vitro conditions.
Main Methods:
- Incubation of bovine longissimus muscle myofibrils in varying ionic strength buffers (0.10–0.35 M KCl or NaCl).
- Analysis of protein solubilization and suspension turbidity over time (1–72 h).
- Gel electrophoresis (SDS-PAGE) to identify released proteins; electron microscopy for structural changes.
Main Results:
- Increased ionic strength and incubation time led to decreased turbidity and increased myofibrillar solubilization.
- KCl and NaCl effectively dissociated M-protein, actin, troponin-T, tropomyosin, and myosin light chain-3.
- pH 5.5 significantly altered the release of specific proteins compared to pH 7.0.
- Thick filament ultrastructure degraded over time, while Z-lines were more resistant unless treated with trypsin.
Conclusions:
- Ionic strength and incubation time are key factors influencing myofibrillar protein solubility and structure.
- Specific protein dissociation patterns vary with salt type and pH.
- These findings provide insights into in vitro muscle protein behavior relevant to meat science.