Applications of molecular graphics to biophysics are reviewed. Biological macromolecules are different from inorganic molecules or synthesized polymers, in that they own their biological information on their tertiary structures. Molecular Graphics are the powerful techiniques, which visualize such information on their tertiary structures to give us deeper understandings to them. There have been four kinds of applications; 1) visualizing their analyzed tertiary structures, 2) assisting analyses of their tertiary structures, 3) predicting their structures, especially those with drug ligands and 4) visualizing their physical, chemical and biological properties and information together with their tertiary structures. Several examples being applied in the field of biophysics are introduced.

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Two types of demembranated cell models have been established using Characeae internodal cells; the tonoplast-free cell model and the plasmalemma-permeabilized cell model. In these models, both ATP and Mg²⁺ were essential for the maintenance of cytoplasmic streaming. Ca²⁺ inhibited the streaming in both models. However, the Ca²⁺-sensitivity of the streaming in the plasmalemma-permeabilized model was 1000 times higher than the tonoplast-free model, suggesting that some Ca²⁺-sensitizing component was dispersed or disorganized by the disintegration of the tonoplast. Using the actin bundles present in the tonoplast-free cells, the streaming was reconstituted with the endoplasm from other Characeae cells or the rabbit skeletal muscle, scallop or Physarum myosin. Ca²⁺ accelearated the streaming reconstituted with scallop myosin but inhibited that reconstituted with Physarum myosin. These opposite effects of Ca²⁺ on reconstituted streamings agree with the effects of Ca²⁺ on the respective actomyosin ATPases.

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Nucleotides play an important role in many metabolic processes. A variety of biologically active fluorescence-labeled nucleotides have been prepared which have proven extremely useful in obtaining information about such processes. For studying energy-transducing biological systems, the use of ribose-modified fluorescent nucleotides are very effective. In this review recently developed ribose-modified fluorescent nucleotides, naphthoyl, 2, 4, 6-trinitrophenyl, anthraniloyl, and N-methylanthraniloyl derivatives, and their application to biological systems, especially the myosin ATPase system, are introduced.

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