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Porcine brain myosin is a cytoplasmic protein similar to, but distinct from, its muscle counterpart. It has a high K+-ATPase activity at high ionic strength in EDTA and a low Mg+2-ATPase activity that is activated fivefold by either porcine brain or rabbit skeletal muscle actin. The molecule consists of three classes of subunits, with molecular weights of approximately 195,000 , 19,000, and 16,000. Brain myosin contains less glutamic acid, less lysine, and more threonine, serine, proline, and tyrosine than skeletal muscle myosin. The brain myosin extinction coefficient at 278 nm is 0.810 cm2/mg. Hydrodynamic studies yield an S020,w of 4.95S, a D020,w of 1.07 x 10(-7) cm2/s for brain myosin, and indicate that the molecules aggregate at high ionic strength. The molecular weight of the molecule, as calculated from extrapolation of D020,w/S20,w to zero concentration, is 444,000. The intrinsic viscosity of brain myosin is 0.191 ml/mg. These data are consistent with a highly asymmetric molecular species. Circular dichroism spectroscopy indicates that brain myosin is 58-60% alpha-helical in the presence of Ca+2 ions, and that removal of Ca+2 causes a small change in the spectrum.

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SUMMARY Microanalytical techniques have been developed for the quantitative determination of actomyosinand collagen from 20 to 30-mg (wet mass) samples of myocardium. Actomyosin is the major contractile protein complex and is, therefore, an index of functional muscle; collagen is the major protein of connective and scar tissue and is, therefore, an index of fibrosis. These proteins were determined in six myocardial samples from each of four normal, four ischemic, and three hypertrophied human hearts. As determined by electrophoresis in a denaturing medium, the concentration of actomyosin in normal myocardium is 69 /tg/mg wet tissue; the concentration in ischemic myocardium is not significantly different from normal, but is approximately 45% higher than normal in hearts with left ventricular hypertrophy. These observations indicate that hypertrophy is not simply an increase in total heart mass but, rather, involves an increase in actomyosin concentration in myocardial tissue as well. Collagen is determined from amino acid analysis of whole tissue for 4-hydroxyproline, an amino acid characteristic of this protein; the concentration of collagen in normal (6.1 /ig/mg wet tissue) myocardium are not significantly different from those in hypertrophied myocardium. In focal regions of ischemic hearts, however, collagen is increased 2-to 4-fold. The concentration of collagen in myocardial tissue correlates well (r = 0.947) with the degree of fibrosis determined by conventional histological techniques. This work represents (1) a more direct biochemical determination of contractile protein concentration in whole myocardium and (2) a more direct correlation of the biochemical assay for collagen with histological data than have been reported previously.