Effect of the N-terminal extension in myosin essential light chain A1 on the mechanism of actomyosin ATP hydrolysis.

Myosin essential light chains A1 and A2 are identical isoforms except for an extension of ∼40 amino acids at the N terminus of A1 that binds F-actin. The extension has no bearing on the burst hydrolysis rate (M-ATP → M-ADP-Pi) as determined by chemical quench flow (100 μM isoenzyme). Whereas actomyosin-S1A2 steady state MgATPase (low ionic strength, 20 °C) is hyperbolically dependent on concentration: V 7.

Demonstration of beta-tropomyosin (Tpm2) and duplication of the alpha-slow tropomyosin gene (TPM3) in Atlantic salmon Salmo salar.

Beta tropomyosin (Tpm2) is demonstrated for the first time at the protein level in a fish species, using a combination of electrophoresis, mass spectrometric peptide mapping and end-group analysis. Tpm2 accounts for 50% of the total tropomyosin in slow trunk muscle of the adult Atlantic salmon as determined by quantitative carboxypeptidase digestion and is also present in the head and pectoral fin. It is absent in the fast skeletal (lighter-toned) trunk muscle, the most abundant muscle, which is composed solely of an alpha-fast (Tpm1) isoform.