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Biomedical subjects

U Jahnke

Publications and source records attributed to U Jahnke.

26 records · Page 2Linked to original sources
PubMed1984

[Not Available].

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Education, Medical↗
PubMed1983

Ca2+ and Mg2+-dependent complex formation of tropomyosin with phosphotroponin (P1TI2C) or dephosphotroponin (TI2C).

The reduced viscosity of troponin and dephosphotroponin is independent of the protein concentration in both states, either metal-free or with troponin C saturated with Ca2+ or Mg2+; that of tropomyosin increases linearly as function of the protein concentration, indicating aggregation. Addition of troponin to tropomyosin increases the reduced viscosity over the expected value being maximal at a 1:1 molar ratio of both proteins. The reduced viscosity of a 1:1 molar mixture of phosphotroponin-Mg4 or dephosphotroponin-Mg3 increases in two phases as function of the total protein concentration, indicating the formation of two kinds of troponin-tropomyosin complexes. In the first phase, troponin and tropomyosin form a non-aggregating 1:1 complex, which is characterized by a value of 0.45 dl/g for the intrinsic viscosity and a sedimentation coefficient of 3.6 S. Employing these two values a molecular weight of 150 000 can be calculated, which is in the range of the sum of molecular weights for troponin and tropomyosin (156 000). In the second phase the troponin-tropomyosin complex aggregates further, a process described by:n (troponin-tropomyosin) leads to (troponin-tropomyosin)n. This further aggregation occurs upon saturation of the Ca2+-specific sites in troponin C. A model is discussed which explains the shortening of 1.5 nm per tropomyosin molecule upon the shift of tropomyosin from the periphery into the groove of the actin filament by tropomyosin aggregation.

Animals↗
PubMed1980

Comparison of the Mg2+ and Ca2+ binding properties of troponin complexes P1-TI2C and TI2C.

The phosphoserine present in troponin T of freshly isolated skeletal muscle troponin P1-TI2C was dephosphorylated by alkaline phosphatase and the resulting troponin TI2C characterized by phosphorous content and gel electrophoresis in presence of sodium dodecylsulfate. Both complexes bind Ca2+ in an identical manner with a K0.5 of 5.3 X 10(-9) M for the Ca2+/Mg2+ binding sites and of 1.1 X 10(-6) M for the Ca2+-specific sites. 3.5 mM Mg2+ lowers the K0.5 value at the Ca2+/Mg2+ binding sites of 1.3 X 10(-7) M in the phospho-troponin P1-TI2C and leaves nearly unchanged the value of the dephosphorylated troponin TI2C at 1.2 X 10(-8) M. At 10 mM Mg2+ only one dissociation constant of about 1.0 X 10(-6) M is determined with both complexes. In analogy dephosphorylation of troponin P1-TI2C reduces the affinity for Mg2+ at the Ca2+/Mg2+ binding sites from 6.7 X 10(-5) M to 2.0 X 10(-3) M. Again the Mg2+-specific sites are uninfluenced. The possibility is discussed that removal of the phosphate group from troponin T allows the interaction of the N-terminal domain of troponin T with other amino acid side chains of troponin.

Alkaline Phosphatase↗