The x-ray structure of chicken skeletal muscle troponin C (TnC), the Ca2+-binding subunit of the troponin complex, shows that the protein is about 70 angstroms long with an unusual dumbbell shape. The carboxyl and amino domains are separated by a single long alpha helix of about nine turns. Only the two high-affinity Ca2+-Mg2+ sites of the COOH-domain are occupied by metal ions resulting in conformational differences between the COOH- and NH2-domains. These differences are probably important in the triggering of muscle contraction by TnC. Also the structure of TnC is relevant in understanding the function of other calcium-regulated proteins, in particular that of calmodulin because of its strong similarity in amino acid sequence.
BERGSTROM, R. M. (1969).A n Entropy Model of the Developing Brain. DEVELOPMENTAL PSYCHOBIOLOGY, 2(3): 139-152.From experimental work on fetal development of neural processes, a qualitative entropy model of the brain is derived. T h e developing brain is structurally organized in a primitive core with a random geometry, surrounded by more highly developed shells with increasing structural order in the connections between neuronal units. Paralleling this development, the sensory-motor transfer function of the brain changes from a transfer of low-grade to high-grade energy. I n proportion to the entropy content of their input and output energies, the core and shells exhibit in their signalling functions different degrees of randomness, with negative entropy of the neural process increasing from the core to the peripheral shells. This implies that the genetic span in the brain is represented as a nonstable domain, which extends structurally from the reticular core to the cerebral cortex, and functionally from the maximum entropy to the maximum negentropy of the system. The nonstable domain, measurable as the difference between the maximum equilibrium and non-equilibrium of the system, represents the information capacity of the brain and increases with the developmental stage of the system. brain developmental neurophysiology maturation central nervous system development entropy models information theory
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