Journal
AMERICAN JOURNAL OF PHYSIOLOGY-HEART AND CIRCULATORY PHYSIOLOGY
Volume 283, Issue 4, Pages H1446-H1454Publisher
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/ajpheart.00274.2002
Keywords
contractile proteins; heart; motility assay; molecular motor
Funding
- NHLBI NIH HHS [HL-52318, HL-66157] Funding Source: Medline
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Two myosin isoforms are expressed in myocardium, betabeta-homodimers (V-1) and betabeta-homodimers (V-3). V-1 exhibits higher velocities and myofibrillar ATPase activities compared with V-3. We also observed this for cardiac myosin from normal (V-1) and propylthiouracil-treated (V-3) mice. Actin velocity in a motility assay (V-actin) over V-1 myosin was twice that of V-3 as was the myofibrillar ATPase. Myosin's average force (F-avg) was similar for V-1 and V-3. Comparing Vactin and F-avg across species for both V-1 and V-3, our laboratory showed previously (VanBuren P, Harris DE, Alpert NR, and Warshaw DM. Circ Res 77: 439-444, 1995) that mouse V-1 has greater V-actin and F-avg compared with rabbit V-1. Mouse V-3 V-actin was twice that of rabbit V-actin. To understand myosin's molecular structure and function, we compared alpha- and beta-cardiac myosin sequences from rodents and rabbits. The rabbit alpha- and beta-cardiac myosin differed by eight and four amino acids, respectively, compared with rodents. These residues are localized to both the motor domain and the rod. These differences in sequence and mechanical performance may be an evolutionary attempt to match a myosin's mechanical behavior to the heart's power requirements.
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