Remembering Jan Amesz (1934-2001): a great gentleman, a major discoverer, and an internationally renowned biophysicist of both oxygenic and anoxygenic photosynthesisa.

We present here the research contributions of Jan Amesz (1934-2001) on deciphering the details of the early physico-chemical steps in oxygenic photosynthesis in plants, algae and cyanobacteria, as well as in anoxygenic photosynthesis in purple, green, and heliobacteria. His research included light absorption and the mechanism of excitation energy transfer, primary photochemistry, and electron transfer steps until the reduction of pyridine nucleotides. Among his many discoveries, we emphasize his 1961 proof, with L. N. M. Duysens, of the "series scheme" of oxygenic photosynthesis, through antagonistic effects of Light I and II on the redox state of cytochrome f. Further, we highlight the following research on oxygenic photosynthesis: the experimental direct proof that plastoquinone and plastocyanin function at their respective places in the Z-scheme. In addition, Amesz's major contributions were in unraveling the mechanism of excitation energy transfer and electron transport steps in anoxygenic photosynthetic bacteria (purple, green and heliobacteria). Before we present his research, focusing on his key discoveries, we provide a glimpse of his personal life. We end this Tribute with reminiscences from three of his former doctoral students (Sigi Neerken; Hjalmar Pernentier, and Frank Kleinherenbrink) and from several scientists (Suleyman Allakhverdiev; Robert Blankenship; Richard Cogdell) including two of the authors (G. Garab and A. Stirbet) of this Tribute.

Mario Ageno and the status of biophysics.

This essay focuses on Mario Ageno (1915-1992), initially director of the physics laboratory of the Italian National Institute of Health and later professor of biophysics at Sapienza University of Rome. A physicist by training, Ageno became interested in explaining the special characteristics of living organisms origin of life by means of quantum mechanics after reading a book by Schrödinger, who argued that quantum mechanics was consistent with life but that new physical principles must be found. Ageno turned Schrödinger's view into a long-term research project. He aimed to translate Schrödinger's ideas into an experimental programme by building a physical model for at least a very simple living organism. The model should explain the transition from the non-living to the living. His research, however, did not lead to the expected results, and in the 1980s and the 1990s he focused on its epistemological aspect, thinking over the tension between the lawlike structure of physics and the historical nature of biology. His reflections led him to focus on the nature of the theory of evolution and its broader scientific meaning.

Wah Soon Chow, a teacher, a friend and a colleague.

To finish this special issue, some friends, colleagues and students of Prof. Chow (Emeritus Professor, the Research School of Biology, the Australian National University) have written small tributes to acknowledge not only his eminent career but to describe his wonderful personality.

Howard Berg's Random Walk through Biology.

This minireview presents the career of biophysicist Howard Berg from his first interest in bacterial chemotaxis and motility through the present. After a summary of some of his early work, a series of reminiscences of students, postdocs, colleagues, and family members is presented. In sum, these recollections capture the effect that Howard's scientific life has had on the field of bacterial chemotaxis and motility and on the careers and lives of those who have interacted with him.

Developments in tandem ion mobility mass spectrometry.

Ion Mobility (IM) coupled to mass spectrometry (MS) is a useful tool for separating species of interest out of small quantities of heterogenous mixtures via a combination of m/z and molecular shape. While tandem MS instruments are common, instruments which employ tandem IM are less so with the first commercial IM-MS instrument capable of multiple IM selection rounds being released in 2019. Here we explore the history of tandem IM instruments, recent developments, the applications to biological systems and expected future directions.

Christiaan Sybesma (August 31, 1928-January 31, 2018), an extraordinary biophysicist of our time.

We provide here a brief Tribute to Christiaan Sybesma (1928-2018), a highly respected biophysicist of our time. We remember him by giving a brief highlight of his life and a glimpse of his outstanding contributions in photosynthesis. He was a charming and highly respected scientist of our time.

Eugene I. Rabinowitch: A prophet of photosynthesis and of peace in the world.

More than 45 years have passed since Eugene I. Rabinowitch died, on May 15, 1973, at the age of 75, but many still remember him as a photosynthesis giant, the author of a 2000-page "Bible" on photosynthesis, a great chemist and physicist, a discoverer of several basic photoreactions, one of the founders of modern biophysics, a peacemaker, a poet, an architect, an artist, a wonderful human being, and above all a great mentor. Sir John Rotblatt cited Eugene Rabinowitch, together with Bertrand Russell, for their key contributions that led to the Nobel Peace Prize awarded in 1995 jointly to Rotblatt and the Pugwash Conferences on Science and World Affairs "for their efforts to diminish the part played by nuclear arms in international politics and, in the longer run, to eliminate such arms." Already in 1965, Eugene Rabinowitch had received the prestigious Kalinga Prize from UNESCO "in recognition of his work to encourage international cooperation among scientists and to bring to light the potential dangers of science to the public."

Tribute in memory of Jacques Breton (1942-2018).

Jacques Breton spent his 39 years of professional life at Saclay, a center of the French Atomic Energy Commission. He studied photosynthesis with various advanced biophysical tools, often developed by himself and his numerous coworkers, obtaining a large number of new information on the structure and the functioning of antenna and of reaction centers of plants and bacteria: excitation migration in the antenna, orientation of molecules, rate of primary reactions, binding of pigments and electron transfer cofactors. Although it is much too short to illustrate his impressive work, we hope that this contribution will help maintaining the souvenir of Jacques Breton as an active and enthusiastic person, full of qualities, devoted to research and to his family as well. We include personal comments from N. E. Geacintov, A. Dobek, W. Leibl, M. Vos and W. W. Parson.

Vyacheslav (Slava) Klimov (1945-2017): A scientist par excellence, a great human being, a friend, and a Renaissance man.

Vyacheslav Vasilevich (V.V.) Klimov (or Slava, as most of us called him) was born on January 12, 1945 and passed away on May 9, 2017. He began his scientific career at the Bach Institute of Biochemistry of the USSR Academy of Sciences (Akademy Nauk (AN) SSSR), Moscow, Russia, and then, he was associated with the Institute of Photosynthesis, Pushchino, Moscow Region, for about 50 years. He worked in the field of biochemistry and biophysics of photosynthesis. He is known for his studies on the molecular organization of photosystem II (PSII). He was an eminent scientist in the field of photobiology, a well-respected professor, and, above all, an outstanding researcher. Further, he was one of the founding members of the Institute of Photosynthesis in Pushchino, Russia. To most, Slava Klimov was a great human being. He was one of the pioneers of research on the understanding of the mechanism of light energy conversion and of water oxidation in photosynthesis. Slava had many collaborations all over the world, and he is (and will be) very much missed by the scientific community and friends in Russia as well as around the World. We present here a brief biography and some comments on his research in photosynthesis. We remember him as a friendly and enthusiastic person who had an unflagging curiosity and energy to conduct outstanding research in many aspects of photosynthesis, especially that related to PSII.

Manfred Eigen: the realization of his vision of Biophysical Chemistry.

Manfred Eigen turned 90 on May 9th, 2017. He celebrated with a small group of colleagues and friends on behalf of the many inspired by him over his lifetime-whether scientists, artists, or philosophers. A small group of friends, because many-who by their breakthroughs have changed the face of science in different research areas-have already died. But it was a special day, devoted to the many genius facets of Manfred Eigen's oeuvre, and a day to highlight the way in which he continues to exude a great, vital and unbroken passion for science as well as an insatiable curiosity beyond his own scientific interests. He continues to dismiss arguments such as, that scientific problems cannot be solved because of a current lack of appropriate tools, or because of the persuasion of the community that certain things are immeasurable. He has lived up to and accepted only the highest scientific standards with his fundamental contributions in widely differing research fields, for which he has received numerous prizes and honorary doctorates, including the Nobel Prize for Chemistry in 1967. Some of his outstanding contributions to science and technology are honored in the following chapters. Here, we will report some characteristic traits of Manfred Eigen, and his personal development. We highlight his visionary foresight regarding how multidisciplinary science should combine to study the complex processes of life and its evolution in establishing an institute that applied biological, chemical, and physical methods, and how his vision became sustained reality.

Colin A. Wraight, 1945-2014.

Colin Allen Wraight, a central figure in photosynthetic electron transfer research since the 1970s, died in Urbana, Illinois, on July 10, 2014. Born in London, England, on November 27, 1945, he had only recently retired from his position as a Professor in Biochemistry, Biophysics & Quantitative Biology, and Plant Biology at the University of Illinois at Urbana-Champaign. Wraight was known especially for his pioneering studies on electron and proton transfer in the photochemical reaction center, and for his careful quantitation of the remarkable quantum efficiency of this device.

Louis Nico Marie Duysens (March 15, 1921-September 8, 2015): a leading biophysicist of the 20th century.

Louis Nico Marie (L. N. M.) Duijsens (Duysens) was one of the giants in the biophysics of photosynthesis. His PhD thesis "Transfer of Excitation Energy in Photosynthesis" (Duysens, 1952) is a classic; he introduced light-induced absorption difference spectroscopy to photosynthesis research and proved the existence of reaction centers, introducing advanced methods from physics to understand biological processes. Further, it is his 1959-1961 seminal work, with Jan Amesz, that provided evidence for the existence of the series scheme for the two light reactions in oxygenic photosynthesis. In one word, he was one of the master biophysicists of the 20th century-who provided direct measurements on many key intermediates, and made us understand the intricacies of photosynthesis with a simplicity that no one else ever did. We present here our personal perspective of the scientist that Lou Duysens was. For an earlier perspective, see van Grondelle and van Gorkom (Photosynth Res 120: 3-7, 2014).

Enhancing the Hodgkin-Huxley Equations: Simulations Based on the First Publication in the Biophysical Journal.

The experiments in the Cole and Moore article in the first issue of the Biophysical Journal provided the first independent experimental confirmation of the Hodgkin-Huxley (HH) equations. A log-log plot of the K current versus time showed that raising the HH variable n to the sixth power provided the best fit to the data. Subsequent simulations using n(6) and setting the resting potential at the in vivo value simplifies the HH equations by eliminating the leakage term. Our article also reported that the K current in response to a depolarizing step to ENa was delayed if the step was preceded by a hyperpolarization. While the interpretation of this phenomenon in the article was flawed, subsequent simulations show that the effect completely arises from the original HH equations.

The Cole-Moore Effect: Still Unexplained?

In the first issue, on the first page of the Biophysical Journal in 1960, Cole and Moore provided the first confirmation of the Hodgkin and Huxley formulation of the sodium and potassium conductances that underlie the action potential. In addition, working with the squid giant axon, Cole and Moore noted that strong hyperpolarization preceding a depolarizing voltage-clamp pulse delayed the rise of the potassium conductance: once started, the time course of the rise was always the same but after significant hyperpolarization there was a long lag before the rise began. This phenomenon has come to be known as the Cole-Moore effect. Their article examines and disproves the hypothesis that the lag reflects the time required to refill the membrane with potassium ions after the ions are swept out of the membrane into the axoplasm by hyperpolarization. The work by Cole and Moore indirectly supports the idea of a membrane channel for potassium conductance. However, the mechanism of the Cole-Moore effect remains a mystery even now, buried in the structure of the potassium channel, which was completely unknown at the time.

Light and life in Baltimore--and beyond.

Baltimore has been the home of numerous biophysical studies using light to probe cells. One such study, quantitative measurement of lateral diffusion of rhodopsin, set the standard for experiments in which recovery after photobleaching is used to measure lateral diffusion. Development of this method from specialized microscopes to commercial scanning confocal microscopes has led to widespread use of the technique to measure lateral diffusion of membrane proteins and lipids, and as well diffusion and binding interactions in cell organelles and cytoplasm. Perturbation of equilibrium distributions by photobleaching has also been developed into a robust method to image molecular proximity in terms of fluorescence resonance energy transfer between donor and acceptor fluorophores.

Model building with wind and water: Friedrich Ahlborn's photo-optical flow analysis.

Around 1900, several experimenters investigated turbulences in wind tunnels or water basins by creating visualizations. One of them, the German zoologist Friedrich Ahlborn (1858-1937), was familiar with the works by his contemporaries but he struck a new path. He combined three different kinds of photographs taken at the same time and showed the same situation in his water trough-but each in a different way. With this first basic operation, Ahlborn heuristically opened up a previously non-existent space for experimentation, analysis, and recombination. He generated an astonishing diversity of information by adopting the tactics of 'inversions' in which he interpreted one part of the experimental setup, or its results, in different ways. Between the variants of the 'autographs' which he developed, he defined areas of intersection to be able to translate results from individual records into each other. To this end, Ahlborn created other sets of visual artifacts such as drawn diagrams, three-dimensional wire frame constructions, and clay reliefs. His working method can be described as a cascading array of successive modeling steps, as elaborated by Eric Winsberg (1999), or of inscriptions in Bruno Latour's words (Latour, 1986). By examining Ahlborn's procedures closely we propose conceptualizations for the experimenter's various operations.

Hugh E. Huxley: the compleat biophysicist.

The sliding filament model of muscle contraction, put forward by Hugh Huxley and Jean Hanson in 1954, is 60 years old in 2014. Formulation of the model and subsequent proof was driven by the pioneering work of Hugh Huxley (1924-2013). We celebrate Huxley's integrative approach to the study of muscle contraction; how he persevered throughout his career, to the end of his life at 89 years, to understand at the molecular level how muscle contracts and develops force. Here we show how his life and work, with its focus on a single scientific problem, had impact far beyond the field of muscle contraction to the benefit of multiple fields of cellular and structural biology. Huxley introduced the use of x-ray diffraction to study the contraction in living striated muscle, taking advantage of the paracrystalline lattice that would ultimately allow understanding contraction in terms of single molecules. Progress required design of instrumentation with ever-increasing spatial and temporal resolution, providing the impetus for the development of synchrotron facilities used for most protein crystallography and muscle studies today. From the time of his early work, Huxley combined electron microscopy and biochemistry to understand and interpret the changes in x-ray patterns. He developed improved electron-microscopy techniques, thin sections and negative staining, that enabled answering major questions relating to the structure and organization of thick and thin filaments in muscle and the interaction of myosin with actin and its regulation. Huxley established that the ATPase domain of myosin forms the crossbridges of thick filaments that bind actin, and introduced the idea that myosin makes discrete steps on actin. These concepts form the underpinning of cellular motility, in particular the study of how myosin, kinesin, and dynein motors move on their actin and tubulin tracks, making Huxley a founder of the field of cellular motility.