Publisher Summary This chapter discusses the mitochondrial respiratory control and the polarographic measurement of ADP : O ratios. The polarographic oxygen electrode technique is used for measuring rapid changes in the rate of oxygen utilization by cellular and subcellular systems. Although the polarographic method measures changes in oxygen concentration of photosynthetic systems, yeast cells, and nerve, but the oxygen electrode technique is applied to a study the mitochondrial respiration and oxidative phosphorytation. The principle of the oxygen electrode has been summarized, and the design of the vibrating oxygen electrode for use with speetrophotometric studies is illustrated. The oxygen electrode apparatus can be calibrated in a number of ways. A more accurate calibration of oxygen content can be obtained by gas equilibration with various nitrogen-oxygen mixtures. When tightly coupled mitochondria are suspended in an isotonic buffer, a slow rate of oxygen uptake is measured in the presence of substrate and absence of ADP. Addition of ADP causes an immediate increase in the rate of oxygen utilization. The concentration of oxygen utilized is proportional to the amount of ADP phosphorylated to ATP. The type of oxygen electrode tracings is presented from which an ADP : O ratio (equivalent to a P : O ratio) can be directly calculated.

[7] Mitochondrial respiratory control and the polarographic measurement of ADP : O ratios

SUMMARY: Results from studies of continuous cultures of Aerobacter aerogenes growing in chemically denned media indicate that specific growth rate (R) is a function of population density (P) as well as the concentration of the limiting nutrient (S). From these observations, and those of others, the following model for bacterial growth is derived: mic-21-1-40-si1.gif where um and B are growth parameters that are constants under defined conditions. This model is believed to have general applicability and to account for bacterial growth in both batch and continuous cultures.

/pdf/kinetics-of-bacterial-growth-relationship-between-population-222gkcebl3.pdf

Kinetics of Bacterial Growth: Relationship between Population Density and Specific Growth Rate of Continuous Cultures

Tissue oxygen tension and brain sensitivity to hypoxia

Presented here is a combined historical account, current synthesis and a perspective of how the modern Fe cycle functions, and how this cycle has evolved through geologic time. We begin by highlighting how new developments in nanogeoscience demonstrate the importance of nanoparticulate Fe (oxyhydr) oxide aggregates in the modern iron cycle. We further document how these aggregates are supplied from shelf sediments, aeolian dust and icebergs to the global ocean. Based on these observations, we present a kinetic model evaluating the supply of bioavailable Fe to surface seawater by ferrihydrite dissolution, photoreduction and siderophore-aided dissolution. The model indicates that the rate of delivery of bioavailable Fe from icebergs to the Southern Ocean is at least as large as that by wind-blown dust. However estimates of all the main aqueous, nanoparticulate and colloidal (and potentially bioavailable) Fe inputs to the ocean are poorly-constrained.

We provide a historical perspective on the evolution of ideas as to how sedimentary pyrite formation is controlled and how these ideas led to the development of the Fe-based palaeoenvironmental proxies widely used today. This provides a springboard into our discussion of the ancient Fe cycle, which begins with a survey of how Fe interacts with a variety of other elements of biogeochemical interest including sulphur, oxygen and nitrogen. We highlight how interactions between these elements have evolved through geologic time, and how these interactions define the evolution of ocean and atmospheric chemistry. It is clear that the Fe cycle has gained a prominent role in regulating the biogeochemical function of the oceans through time. We offer, in the end, suggestions and a geochemical perspective as to how recent momentum in our understanding of the Fe cycle may be harnessed into catalysing future progress in the field.

I. S. Longmuir

Papers

Respiration rate of bacteria as a function of oxygen concentration.

The nature of the initial reaction of oxygen with two bacterial cytochrome oxidases