Ubiquitin-calmodulin conjugating activity from cardiac muscle

Enzyme activity capable of covalently linking ubiquitin to bovine calmodulin in an ATP-dependent manner has been detected in rabbit cardiac muscle demonstrating that this enzyme occurs not only in reticulocytes but also in other tissues and possibly all tissues and cells which contain calmodulin as intracellular Ca2+-acceptor protein. This is of special interest since a ubiquitin-dependent proteolytic activity could previously not be detected in cardiac muscle. The name ubiquityl-calmodulin synthetase [uCaM-synthetase, ubiquityl:calmodulin ligase (EC 6.3.?.?)] is therefore suggested for this enzyme. In crude cardiac muscle extracts uCaM-Synthetase displays a specific activity of 93 nUnits/mg in comparison to reticulocyte lysate with 270 nUnits/mg as measured by the fluphenazine-Sepharose affinity adsorbent test (FP-test). Analysis of the ubiquitination product (125I-uCaM) by polyacrylamide electrophoresis in the presence of SDS followed by autoradiography reveals a major double band with molecular masses of 27 and 29 kDa (mono-ubiquitination products) respectively. In addition two novel minor bands (17 and 20 kDa) of smaller molecular mass than the monoubiquitination products were detected. These are probably proteolytic breakdown products of uCaM. A model is suggested for a specific function of this synthetase in the Ca2+-dependent breakdown of calmodulin in vertebrate (eukaryotic) cells.     

Catalase in skeletal muscle fibers.

Catalase has been localized immunocytochemically with anti-bovine catalase in long thin filament structures in aerobic type I fibers in the skeletal muscles of normal and genetically dystrophic hamsters. The filaments range in length from 1 to 60 micron, are orientated regularly along the long axis of the fibers, and also seem to surround and project from muscle nuclei. The enzyme thus appears to be more prominent in the sarcoplasmic reticulum than in peroxisomes, and in this situation is suitably placed for destroying toxic hydrogen peroxide which may be continously generated in aerobic fibers.     

Catalase activity of hydrocarbon-oxidizing bacteria

The dynamics of catalase activity of the hydrocarbon-oxidizing bacteria Gordona terrae, Rhodococcus rubropertinctus, and Rhodococcus erythropolis during petroleum product destruction has been studied. A direct relationship between decreasing catalase activity of hydrocarbon-oxidizing microorganisms and the intensity of petroleum product destruction has been established experimentally. The revealed dependence allows one to consider the catalase activity of bacteria as an indicator of the initial stage of petroleum product oxidation and may be used for choosing destructor strains to construct biopreparations suitable for natural ecosystem remediation.     

Chloride activity and its control in skeletal and cardiac muscle

Ion-selective microelectrodes have been used to compare the mechanisms controlling intracellular Cl- activity in skeletal and cardiac muscle. In frog Sartorius skeletal muscle fibres, Cl- levels are low (about 3 mM) and are determined mainly passively. The effect of any Cl- transport system will be quickly short-circuited through the high membrane Cl- conductance. In contrast, the sheep-heart Purkinje fibre, like other cardiac tissues, contains higher than passive levels of intracellular Cl- (20-30 mM). Many Cl- movements occur, not through Cl- channels (the permeability for Cl- is low), but by a Cl- -HCO3- countertransport system. High internal Cl- levels are achieved by an exchange of extracellular Cl- for intracellular HCO3-, which acidifies the fibre by 0.3 pH. Anion exchange in heart differs from that proposed for other excitable cells in that it is not specialized to compensate for an intracellular acidosis. Instead, it can prevent the fibres from becoming too alkaline by promoting a bicarbonate efflux and a chloride influx whenever internal bicarbonate levels rise. Possible reasons for this are briefly discussed.     

Carbonic anhydrase activity in mammalian skeletal and cardiac muscle.

1. The presence of extravascular carbonic anhydrase activity in skeletal muscle, and its absence from cardiac muscle, were demonstrated in the rat. 2. The activity in skeletal muscle is approximately correlated with the proportion of dark fibres present in the middle fibre bundles.     

DNA synthesis and DNA polymerase activity in differentiating cardiac muscle

DNA synthesis in cardiac muscle of the rat declines rapidly following birth and is essentially “turned off” by the 17th day of postnatal development. Soluble DNA polymerase activity also decreases progressively with age, reaching adult levels of almost zero by the 17th day of development. These results indicate that cessation of DNA synthesis in differentiating cardiac muscle may be attributed to the loss or inactivation of DNA polymerase.