Delbriick

Max Delbriick Center for Molecular Medicine (MDC), Berlin-Buch, Germany... 

See Fischer and Lipscomb (1988) Sarkar (1989) reconstructs the history of Delbriick s idiosyncratic anti-reductionism and the influence on him of Bohr s hope for the discovery of complementarity in biology. 

Fig. 5. Four basic illumination programs and their outputs. The top row gives the program, intensity I (linear scale) versus time t. The bottom row gives the growth output, velocity (relative to average velocity) versus time. The second and third row give the level of adaptation A, and the subjective intensity, i = I/A, calculated according to the theory developed. Note that the scale used to plot i(t) is twenty times larger for the down than for the up programs. (From Delbriick and Rei-chardt, 1956)...

Another way to express this fact is to say that the sensitivity of the system changes with the light intensity of the pretreatment. This led Delbriick and Reichardt (1956) to introduce the concept of level of adaptation, A. The level of adaptation, A, is postulated to be a biophysical or biochemical status of the cell and its magnitude is somehow proportional to the intensity of light used in the pretreatment. They assumed that after a long pretreatment at constant intensity the adaptation reaches an equilibrium with intensity, formally A = I0. 

Delbriick and Reichardt tried with a simple and elegant mathematical formulation to explain two very different effects which are caused by changes of light intensity ... 

The growth rate, however, always returns to the baseline level less than 30 min after the stimulus as shown in Fig. 7. This observation demonstrates that the model is not correct for the growth response as there must be at least two biochemical steps along the light sensory transduction chain which are subject to regulation. One sets the level of sensitivity and the other is responsible for the return of growth rate to the base-line level. Only the first step which sets the level of sensitivity obeys the simple differential equation of Delbriick and Reichardt and only then in cases where a small stimulus was employed. 

To understand the molecular mechanism of phototropism it is essential to know whether adaptation is localized in a defined region of the cell or whether it is spread throughout the cell. To determine this Delbriick and Vaiju (1961) performed a series of experiments in which they stimulated the sporangiophore with ultraviolet light in sharply bounded and narrow test areas (line width of 0.2 mm). They found that the... 

Fig. 15. Action spectra for growth response and tropic response. (From Delbriick and Shropshire, 1960)...

Delbriick et al., (1976) have recently sought to determine whether or not the stimulation of Phycomyces involves the excitation of the lowest triplet state of riboflavin. They determined an action spectrum of light-growth response between 575 and 630 nm using a tunable laser beam and taking advantage of the null method described above. This action spectrum was compared with an action spectrum obtained by computer extrapolation of a phototropic action spectrum covering 445—560 nm. 

A final criterium for the photoreceptor would be its presence at an adequate concentration. On the basis of a few reasonable assumptions Delbriick estimated the minimal theoretical concentration for photoreceptor to be about 3 x 10-7m corresponding to 109 receptor molecules per growing zone (in Bergman et al., 1969). 

Delbriick, M., Reichardt, W. Cellular Mechanism in Differentiation and Growth, pp. 3-44. 

Princeton Princeton University Press 1956 Delbriick, M., Shropshire, W. Plant. Physiol. 35, 194 (1960)... 

L. Pauling, M. Delbriick, Nature of the intermolecular forces operative in biological processes , Science, 1940, 92, 77-79. 

D6. Delbriick, A., and Poschmann, H., Uber den einfluss des rohrposttransportes auf klinisches untersuchungs material unter verschiedenen betriebsbedingungen. Z. Klin. Chem. Klin. Biochem. 6, 211-216 (1968). 

---