Triad Formation Research Articles

Determinants of triad junction reformation: identification and isolation of an endogenous promotor for junction reformation in skeletal muscle.

The junction of isolated triads can be mechanically broken by passage through a French press and subsequently reformed by incubation of the isolated organelles with certain salts of weak acids (e.g., K cacodylate, K propionate, and K butyrate). In contrast, other salts (e.g., KCl, K phosphate, and K benzoate) are ineffective in promoting triad formation. An endogenous factor obtained from a muscle homogenate acts in the same manner as these artificial compounds. When rabbit skeletal muscle is homogenized in a KCl solution and centrifuged to remove large cellular components and membrane fractions, an endogenous factor is extracted into the high speed supernatant which promotes the reformation of mechanically broken triads. A three-stage purification of this factor has been achieved using: ammonium sulfate fractionation, adsorption chromatography, and molecular sieve chromatography. SDS-PAGE showed that the protein was purified to homogeneity and had a subunit Mr of 34,000 daltons. This protein has the following characteristics: it exists in 0.1 M KCl as a polymeric substance with an estimated Mr = 123,000 on molecular sieve chromatography and a Mr = 155,000 on sedimentation equilibrium; it promotes the formation of triadic vesicles from isolated organelles in a low ionic strength medium; Both this protein and cacodylate share the property of specifically catalyzing the association and aggregation of junctional proteins which had previously been dissolved by neutral detergent and salt; it appears to be identical to an extrinsic constituent of terminal cisternae, which has been described as a protein of Mr = 34K. It is not clear, however, whether this protein is a necessary and integral component of the junctional feet or whether it exerts predominantly a catalytic role in the formation of the triad junction.

Genome relationships between Hordeum procerum (6x) and H. lechleri (6x)

Investigations on the meiotic behaviour of chromosomes in interspecific hybrids (2n=6x=42) between Hordeum lechleri (6x) and H. procerum (6x) and in their component haploids have been utilized to assess the nature of pairing and the extent of genome homology between the two species. In the F1 hybrids an average of 25 (60%) chromosomes associated at metaphase I, mostly as bivalents. A majority (60%) of the pollen mother cells (PMCs) in H. procerum haploids (2n=3x=21) displayed 21 univalents and even in the remainder, a maximum of two rod bivalents were formed resulting in an average of 0.52 bivalents per cell. In haploids of H. lechleri (2n=3x=21) however, 30% of chromosomes pair. The sum of the chromosomal associations in the component haploids represents only 17% of the complement, far below the observed frequency (60%) in the hybrids. Thus, the pairing displayed in hybrids between H. lechleri and H. procerum was mostly allosyndetic and suggestive of two genomes being common in these species. In haploid H. procerum 1/3 of the PMCs displayed a tripolar organisation of chromosomes leading to triad and hexad formation after divisions I and II respectively. The significance of hexad formation in the trihaploid H. procerum and a possible suppression of homoeologous pairing in H. procerum haploids are discussed.

Thermodynamics and the equilibrium state of a binary copolymer that is determined by next‐nearest neighbor intrachain effects

AbstractThe equilibrium state of an infinite molecular weight, binary copolymer which is determined by next‐nearest neighbor placements of its counits is defined in terms of the conditional probabilities describing such placements and the standard state free energies governing them. The combinatorial method is used to derive the entropy of sequence length distribution, ΔSD. When ΔSD is combined with an expression for the energy of reaction which employs the standard‐state free energies of triad formation an expression for the copolymer's free energy is obtained. Since enumeration of the interrelationships among the possible triplets reveal three independent conditional probabilities, separate differentiations with respect to each of three conditional probabilities are equated to zero in defining the equilibrium state. These equations reduce to the more special case previously derived when only nearest‐neighbor effects are considered.