The pulse radiolysis technique is based on a perturbation of a system by a short pulse (<1μsec) of high energy radiation. This technique has been employed for the study of the mechanism of action of the oxidation-reduction proteins with high time resolution. This review deals with studies of pulse radiolisis in biological systems: (1) principles, (2) experimental methods, (3) examples, and (4) the mechanism of reduction of electron transfer proteins by hydrated electron (eaq-). The eaq- reacts with the redox site of electron transfer protein good yield, compared with other proteins. This reduction is assigned mainly to a direct reaction proceeding via the exposed edge of the redox site. In other cases, eaq- does not reduce the redox site in the protein and reacted with the amino acid residues. These results suggests that electron captured by the protein does not necessarily migrate the redox site in the protein.
The prestalk/prespore pattern within a slug of the cellular slime molds presents a simple model system to the studies of biological pattern formation. Formation of a slug is accompanied by differentiation of prestalk and prespore cells which occupy the front part and the rear part of a slug, respectively. The proportion of the prestalk to prespore cells is regulated to be constant irrespective of the slug size. Isolated prespore and prestalk portion can regenerate the normal pattern by cell type conversion. Many experiments indicate that sorting out of the cells play an important role in both formation and regulation of the pattern. Differences between prestalk and prespore cells in chemotaxis toward cAMP are likely to be involved in the sorting out. Cells similar to prestalk cells in many respect are scattered in the prespore region. They are different from prestalk cells in behaviour and called "anterior-like cells". Our observations indicate that they are constantly exchanging with prestalk cells during migration of the slug. Several experimental systems have been deviced in which cells can differentiate without morphogenesis. It has also been found that the normal spatial pattern of prestalk and prespore cells is not necessarily required of the proportion regulation between them.