Key result
Semimembranosus myosin demonstrates lower heat stability than vastus intermedius at ultimate but not matched pH.
Why the study?
The thermal behaviors and heat stability of myosin from two bovine muscle types at their respective ultimate pH values were compared to understand differences in denaturation and aggregation.
The thermal stability of bovine myosin depends on both the muscle type (red vs. white) and the pH environment.
Bovine findings warrant no clinical changes; leaves open isoform-specific myosin research in human cardiac muscle.
The thermal behaviors of myosin from bovine vastus intermedius (VI, predominantly red muscle) and semimembranosus (SM, predominantly white muscle) at pH 6.05 (ultimate pH of VI muscle) and 5.50 (ultimate pH of SM muscle) were compared. Differential scanning microcalorimetry and turbidity measurements were used to monitor changes in myosin during heating from 25 to 80 degrees C at 1 degrees C/min. VI and SM myosin heavy chain isoforms were identified on gradient SDS-PAGE. Endotherms of VI myosin at pH 6.05 had three transition temperatures (T(m)) of 45, 53, and 57 degrees C, whereas at pH 5.50 two transitions were observed at 42 and 59 degrees C. SM myosin had two T(m) values of 46 and 58 degrees C at pH 6.05 and T(m) values of 43 and 62 degrees C at pH 5.5. SM myosin at its ultimate pH was less heat stable than VI myosin at its ultimate pH; however, when SM and VI myosin were compared at the same pH, VI myosin was less stable.
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Vega-Warner et al. (2001) studied this question. Bovine muscle myosin (vastus intermedius vs semimembranosus) at different pH levels was evaluated on Thermal transition temperatures (Tm). Semimembranosus myosin at its ultimate pH was less heat stable than vastus intermedius myosin at its ultimate pH, but vastus intermedius myosin was less stable when compared at the same pH.
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