The effect of cross-innervation on the tropomyosin composition of rabbit skeletal muscle.

Soleus, semitendinosus and crureus muscles of the rabbit were found to contain alpha- and beta-tropomyosin subunits and additional forms that have been provisionally designated gamma and delta. Extensor digitorum longus and psoas muscles contained only alpha and beta subunits, the relative proportions of which varied between single fibres of psoas muscle. On cross-innervation of rabbit soleus and extensor digitorum longus muscles, the fraction of the total tropomyosin present as the beta subunit remained constant. The relative proportions of alpha, gamma and delta subunits changed as would be expected from the change in speed that occurred.

Proteins in the urine associated with Duchenne muscular dystrophy and other neuromuscular diseases.

1. Up to 200 protein staining spots could be detected on two-dimensional electrophoresis of urine from healthy persons. Other minor spots were occasionally present. 2. Although the electropherograms exhibited constant characteristic features some variation in protein pattern was observed between individuals and with a given individual at different times. 3. Two additional proteins, spots C and D, were consistently present in urine from boys with Duchenne muscular dystrophy. Spot C was also present in the urine of about 60% of obligatory carriers of this dystrophy. 4. The protein responsible for spot C had a molecular weight of 26000 and an isoelectric point of 5.3. 5. Spot C was also detected in the urine of patients with other neuromuscular conditions. Neither spot C nor spot D could be detected in the urine of patients with physical disabilities other than those of neuromuscular origin. 6. It is concluded that the urinary excretion of spot C, and probably of spot D, is a consequence of muscle damage and that their detection has potential as a diagnostic tool.

A protein in urine associated with muscle disease and muscle damage.

Analysis of the protein composition of human urine by high-resolution two-dimensional electrophoresis showed that several features are associated with neuromuscular diseases, the best defined being the appearance in the urine of a small amount of a protein that migrates on the electropherogram as a characteristic spot (spot C). This spot consists of a protein of apparent molecular weight 26 000 and isoelectric point 5.3. The spot was usually present in the urine of patients suffering from diseases in which the musculature was directly affected but was rarely found in other patients and normal subjects. The protein responsible for spot C appears to be an index of muscle damage caused by a number of conditions. Attempts are being made to isolate enough of the protein to permit its identification.

Phosphorylation of cardiac myofibrillar proteins.

The P light chain of cardiac myosin is phosphorylated and dephosphorylated by highly specific enzymes. These reactions take place in the beating rabbit heart and there is evidence that dephosphorylation of the light chain occurs during the inotropic response produced by adrenaline. The extent of phosphorylation of cardiac troponin I is determined by the functional state of the beating heart. During perfusion of the rabbit heart the basal phosphate content of troponin I increased from the basal level of about 1.5 moles P per mole to about 2.7 moles P per mole at the height of the inotropic response to adrenaline. The three sites of phosphorylation on troponin I are probably located in the N terminal cyanogen bromide peptide of 48 residues.

Phosphorylation of the light-chain components of myosin from cardiac and red skeletal muscles.

1. The light-chain components of myosin from cardiac muscle (19000 and 27000 daltons) and of rabbit soleus and crureus muscles (19000, 27000 and 29000 daltons) were characterized. 2. The 19000-dalton components in carciac- and red-skeletal-muscle myosins were spontaneously modified to a component of slightly higher net negative charge. 3. The 19000-dalton component in cardiac and red skeletal muscles and their modified forms were phosphorylated by myosin light-chain kinase. 4. Evidence was obtained for the presence of myosin light-chain kinase in cardiac and red skeletal muscles. 5. Myosin light-chain kinase catalysed the phosphorylation of the whole light-chain fraction from white and red skeletal muscle at similar rates. The light-chain fraction of cardiac-muscle myosin was phosphorylated at a significantly lower rate. 6. The light-chain components of cardiac-muscle myosin and their phosphorylated froms were separated by ion-exchange chromatography and their amino acid compositions determined.

The effects of environmental temperature on the properties of myofibrillar adenosine triphosphatase from various species of fish.

1. Myofibrillar adenosine triphosphatase (ATPase) activities were measured for white myotomal muscle of 19 species of fish. 2. The activity was measured at different temperatures and after periods of preincubation at 37 degrees C. 3. The inactivation half-life at 37 degrees C depended on environmental temperature, increasing as the temperature increased. 4. Cold-water fish had higher myofibrillar adenosine triphosphatase activity at low temperatures than had warm-water fish. 5. The significance of these results is discussed.