It has long been recognized that measurements of the permeability characteristics of membranes (and of epithelia) may be strongly influenced by the presence of unstirred, or diffusion, layers adjacent to the membranes: see Dainty (1963) for the first systematic discussion of the subject in a biological context and Barry & Diamond (1983) for an important recent review. Consider a homogeneous, plane, uncharged membrane separating two solutions of the same solute at different bulk concentrations Cb+ and Cb- (Fig. 1), but at the same hydrostatic pressure and electrostatic potential (note that in this paper subscripts + and − refer to the two sides of the membrane, not to cation and anion parameters; electroneutrality is assumed throughout).

The principle of the microprobe analysis of chemical elements is illustrated in Fig. i. Some kind of radiation is directed on to the specimen, generating signals characteristic of the elements present. Local analysis in situ is achieved in one of two ways. Most often the impinging beam is finely focused so that the signal at any moment comes only from a selected microregion. Alternatively, in some instruments, the impinging beam floods a larger region but the emergent signals characteristic of a particular element may be selected and focused to give an elemental ‘map’ or ‘image’.

Selection in biochemical synthesis processes is a very important task: processes as protein or nucleic acid synthesis must be very accurate although the cell abounds with closely related molecules which, intuitively, should be difficult to distinguish. The mechanisms of selection and the underlying processes have been extensively studied in the last years, and the ideas have been developed into mathematical models to visualize the potentials of recognition and error correction. There are several aspects on this, the main aspect of the present work being the important fact that the cell must pay for the increased accuracy in terms of available free energy: processes are driven from equilibrium, and do away with appreciable dissipation.

The experimental observations described in this article indicated that a distribution of many different fluctuations is present in a globular protein. These fluctuations were characterized by observation of many natural internal probes such as the labile peptide protons and the aromatic side chains. The conditions which are necessary to get reactions of the internal probes have been discussed in detail. The structural interpretation of the data was facilitated by the development and the use of new NMR techniques which provided the identification of the resonances of all the labile peptide protons. With NOE measurements a distinction between correlated and uncorrelated exchange events was obtained. This enabled us to elucidate the exchange mechanism over a wide range of p2H and temperature and to classify different subsets of fluctuations with respect to their lifetimes. It was further demonstrated that a change of external conditions such as temperature, p2H or pressure can change the distribution of fluctuations in the protein. The mechanisms responsible for rotation of internal aromatic side chains were also found to change with temperature, and mechanistic aspects of these fluctuations were discussed.

Piezoelectricity and pyroelectricity in wool and hair were observed by Martin early in 1941. The piezoelectric effect in wood was investigated in detail by Bazhenov (1961). Both converse and direct effect of shear piezoelectricity in wood was demonstrated by Fukada (1955). Bending piezoelectricity in bone was first discovered by Yasuda (1953). Shear and longitudinal piezoelectricity in bone and tendon was quantitatively investigatged by Fukada & Yasuda (1957, 1964).

Though the structures presented in crystallographic models of macromolecules appear to possess rock-like solidity, real proteins and nucleic acids are not particularly rigid. Most structural work to date has centred upon the native state of macromolecules, the most probable macromolecular form. But the native state of a molecule is merely its most abundant form, certainly not its only form. Thermodynamics requires that all other possible structural forms, however improbable, must also exist, albeit with representation corresponding to the factor exp( — Gi/RT) for each state of free energy Gi (see Moelwyn-Hughes, 1961), and one appreciates that each molecule within a population of molecules will in time explore the vast ensemble of possible structural states.

Single unit recordings have provided us with a basis for understanding the auditory system, especially about how it behaves under stimulation with simple sounds such as clicks and tones. The experimental as well as the theoretical approach to single unit studies has been dichotomous. One approach, the more familiar, gives a representation of nervous system activity in the form of peri-stimulus-time (PST) histograms, period histograms, iso-intensity rate curves and frequency tuning curves. This approach observes the neural output of units in the various nuclei in the auditory nervous system, and, faced with the random way in which the neurons respond to sound, proceeds by repeatedly presenting the same stimulus in order to obtain averaged results. These are the various histogram procedures (Gerstein & Kiang, 1960; Kiang et al. 1965).

In a living cell membrane-bound compartments are continuously either separated or united through fusion reactions, and literally thousands of such reactions take place every minute. The formation of membrane vesicles from pre-existing membranes, and their fusion with specific acceptor membranes, constitute a prerequisite for the transport of most impermeant molecules and macromolecules into the cell by endocytosis, out of the cell by exocytosis, and between the cellular organelles (Palade, 1975; Silverstein, 1978; Evered & Collins, 1982). Less frequent, but equally crucial, are fusion events in fertilization, cell division, polykaryon formation, enucleation, etc. (for reviews see Poste & Nicholson, 1978). Although a great deal is known about the properties and consequences of individual forms of membrane fusion in cellular systems, and about fusion in artificial lipid membranes, the molecular basis for the reactions remain largely unclear.

Photosynthesis in green plants or algae may be represented by an overall equation:

The energy necessary to promote this overall reaction is derived from light through absorption by pigment molecules — chiefly the chlorophylls.

Photosynthesis occurs in chloroplasts - subcellular organelles in which all the chlorophyll pigments are located. The chloroplasts comprise membranous, structures, and can be classified into two types. To the first type belong chloroplasts with appressed stacks of lamellar membranes, termed grana. These chloroplasts occur in mesophyll cells (C3 plants). The second type of chloroplasts are those with lamellar membranes that do not form the grana structures; they occur in bundle sheath cells of maize and other monocotyledons (C4plants, Hatch & Slack, 1970). In algae a greater diversity of structure occurs (Kirk & Tilney-Basset, 1978). Fluorescence microscopy indicates that chlorophyll molecules are localized mainly in the grana membrane regions of mesophyll-type chloroplasts and uniformly throughout the bundle sheath cells (Spencer & Wildman, 1962). Mesophyll chloroplasts are flattened saucer-shaped organelles (20 or more in each cell) of between 5000 and 10000 nm in diameter, and of thickness 1000–2000 nm, whilst the individual grana are each of the order of 300–500 nm in diameter. The available evidence suggests that individual lamellar membranes are arranged to form vesicles, or sacks where the internal space is completely delimited from the external space. These individual closed membrane structures were termed thylakoids (Menke, 1962).

We shall not attempt here to enumerate the results or review in a systematic way the significant literature dealing with the use of high pressure in studies of proteins and other molecules of biological interest. Two recent reviews on this subject, one by MOrild (1981) and another by Heremans (1982), and a further article by Jaenicke (1981) on enzymes under extreme environmental conditions contain expositions and references that would render redundatn such a task. Rather we concentrate here on the examination of othe conceptual framework employed in the interpretation of high pressure experiments and in the critical discussion of our knowledge of selected areas of present interest and likely future significance.