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R Dabrowska

Publications and source records attributed to R Dabrowska.

At least 73 records · Page 4Linked to original sources
PubMed1982

Calcium-independent myosin light chain kinase of smooth muscle. Preparation by limited chymotryptic digestion of the calcium ion dependent enzyme, purification, and characterization.

Limited alpha-chymotryptic digestion of Ca2+-, calmodulin-dependent myosin light chain kinase partially purified from smooth muscle (turkey gizzard) yielded a Ca2+-independent form of the enzyme. Digestion to yield the Ca2+-independent kinase required the enzyme complexed with Ca2+-calmodulin; when digestion was performed on the apoenzyme, i.e., in the absence of Ca2+, the dependence of kinase activity on Ca2+ was retained. The Ca2+-independent kinase was purified by ion-exchange chromatography and shown to have an apparent molecular weight of approximately 80000. The specific activity of the freshly prepared enzyme was 6.5 +/- 0.2 mumol of Pi incorporated min-1 mg-1 in the presence of Ca2+ and 8.3 +/- 0.3 mumol min-1 mg-1 in the absence of Ca2+, using the isolated light chains of gizzard myosin as the substrate. The Ca2+-independent enzyme also phosphorylated the 20000-dalton light chains of purified myosin and crude actomyosin from turkey gizzard. The Km of the Ca2+-independent kinase for Mg2+-ATP (54 muM) was not significantly different from that of the native, CA2+-dependent enzyme (68 muM). These observations indicate maintenance of the integrity of the active site after digestion with alpha-chymotrypsin. It is suggested that the loss of Ca2+ sensitivity of the kinase after limited proteolysis is due to loss of the calmodulin-binding site from the 80000-dalton fragment. The two sites of phosphorylation by the cyclic AMP dependent protein kinase were also removed by the chymotryptic hydrolysis.

Animals↗
PubMed1979

Calcium-sensitive regulation of actin-myosin interactions in baby hamster kidney (BHK-21) cells.

A fraction has been obtained from baby hamster kidney (BHK-21) cells that will stimulate the actin-moderated ATPase (ATP phosphohydrolase, EC 3.6.1.3) activity of both BHK-21 myosin and gizzard smooth muscle myosin. This activation is associated with the specific phosphorylation of the myosin 20,000-dalton light chain. The BHK-21 myosin light chain kinase preparation contains a major protein of approximately 105,000 molecular weight as determined by sodium dodecyl sulfate gel electrophoresis. Both the actin activation and phosphorylation events require the presence of Ca2+ and the so-called modulator or calcium-dependent regulator protein that has been isolated from smooth muscle, brain, and other tissues. On the basis of these results we propose that this kinase system constitutes a Ca2+-dependent regulatory mechanism for myosin-actin interactions in nonmuscle mammalian cells.

Actins↗
PubMed1978

Modulator protein as a component of the myosin light chain kinase from chicken gizzard.

The Ca2+-dependent regulation of smooth muscle actomyosin involves a myosin light chain kinase (ATP: myosin light chain phosphotransferase). It has been shown (Dabrowska, R., Aromatorio, D., Sherry, J.M.F., and Hartshorne, D.J. 1977, Biochem. Biophys. Res. Commun. 78, 1263) that the kinase is composed of two proteins of approximate molecular weights 105 000 and 17 000. In this communication it is demonstrated that the 17 000 component is the modulator protein. This conclusion is based on: (1) the identical behavior of the 17 000 kinase component and modulator protein in assays of actomyosin Mg2+-ATPase activity, phosphorylation of myosin, and phosphodiesterase activity, and, (2) the similarity of the 17 000 kinase component and the modulator protein with respect to amino acid composition, absorption spectrum, and electrophoresis in urea-polyacrylamide gels. It is shown also that the modulator protein from smooth muscle and troponin C are distinct proteins.

Adenosine Triphosphatases↗
PubMed1976

Calcium regulation in heart cells. The interaction of mitochondrial and sarcoplasmic reticulum with troponin-bound calcium.

A study has been carried out of the interaction of dog heart mitochondria and sarcoplasmic reticulum with Ca2+ bound to troponin or to its Ca2+-binding component (troponin-C). Both organelles are able to release more than 80% of the Ca2+ bound to the two proteins. However, sarcoplasmic reticulum is only able to do so in the presence of oxalate, whereas mitochondria are active also in the absence of permeant Ca-complexing anions. On the other hand, calcium uptake in heart mitochondria is severely inhibited by Mg2+. The results are discussed with reference to the problem of the control of Ca2+ in heart sarcoplasm.

Animals↗
PubMed1976

Interaction of tropomyosin with troponin components.

1. The TN-T and TN-I components of troponin both interact with tropomyosin and cause its precipitation in 0.1 M KC1 at neutral pH. The precipitate contains both end-to-end and side-by-side aggregates of tropomyosin molecules. 2. The TN-T and TN-I components change the band pattern of tropomyosin paracrystals formed in MgC1(2) solutions, although in different ways. TN-T causes the formation of hexagonal net structures, double-stranded net or paracrystals which result from the collapse of the double-stranded net. TN-I at pH 7.9 causes the formation of paracrystals with a 400 A periodic band pattern and a 200 A repeat. The same band pattern can also be seen in tropomyosin paracrystals formed at pH values below 6.0. 3. The TN-C component does not precipitate tropomyosin in 0.1 M KC1. The aggregates of tropomyosin obtained with either TN-T or TN-I can be solubilized by the addition of TN-C. No interaction of TN-C was observed with tropomyosin paracrystals formed in the presence of MgC12.

Animals↗
PubMed1975

Interaction of troponin components with F-actin and F-actin-tropomyosin complex.

1. Both TN-T and TN-I components of troponin interact with F-actin, causing its precipitation at 0.1 M KC1 and neutral pH in a form of highly ordered paracrystals, although the ability of TN-I component to precipitate of F-actin is much weaker. 2. F-actin paracrystals obtained in the presence of both TN-T and TN-I components consist of parallel arrays of F-actin filaments, although the fine structure is in each case different. 3. In the presence of tropomyosin in the proportion equal to that in muscle, less TN-T or TN-I component is needed to obtain full precipitation of F-actin. 4. Paracrystals of F-actin-tropomyosin-TN-T component and F-actin-tropomyosin-TN-I component show regular transverse striation spaced at about 380 A intervals. 5. The TN-C component of troponin solubilizes all precipitates of F-actin with TN-T or TN-I components, regardless of the presence of tropomyosin. 6. The results show that both TN-T or TN-I components can bind independently to F-actin-tropomyosin complex with the same periodicity, similar to that of the whole troponin in the living muscle.

Actins↗
PubMed1975

Composition of cardiac muscle troponin.

Preparations of troponin from cardiac muscle consist of functionally the same subunits as skeletal troponin, that is TN-T, TN-I, and TN-C. Cardiac TN-T and TN-I have, however, higher molecular weights than those of skeletal muscle. Only TN-C from both sources does not differ in respect to the molecular weight, isoelectric point, and ability to bind calcium or strontium.

Animals↗