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Related Concept Videos

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Channel Rhodopsins

Most organisms use photoreceptors to sense and respond to light. Examples of photoreceptors include bacteriorhodopsins and bacteriophytochromes in some bacteria, phytochromes in plants, and rhodopsins in the photoreceptor cells of the vertebral retina. The light-sensitive property of these receptors is because of the bound chromophores, such as bilin in the phytochromes and retinal in the rhodopsins.
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Red algae, also known as rhodophytes, are primarily found in marine environments, though some species inhabit freshwater and terrestrial ecosystems. These organisms exist in both unicellular and multicellular forms, with some multicellular varieties reaching macroscopic sizes.As phototrophic organisms, red algae contain chlorophyll a; however, their chloroplasts lack chlorophyll b. Instead, they possess phycobiliproteins, which serve as major light-harvesting pigments, similar to those found in...
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Reaction centers are pigment-protein complexes that initiate energy conversion from photons to chemical entities. Therefore, photochemical reaction center is a more appropriate term that describes these complexes. The Nobel laureates Robert Emerson and William Arnold provided the first experimental evidence of photochemical reaction centers by demonstrating the participation of nearly 2,500 chlorophyll molecules for the release of just one molecule of oxygen. Despite thousands of photosynthetic...
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The equilibrium binding constant (Kb) quantifies the strength of a protein-ligand interaction. Kb can be calculated as follows when the reaction is at equilibrium:

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Related Experiment Video

Updated: Jun 19, 2026

Measuring Cation Transport by Na,K- and H,K-ATPase in Xenopus Oocytes by Atomic Absorption Spectrophotometry: An Alternative to Radioisotope Assays
12:48

Measuring Cation Transport by Na,K- and H,K-ATPase in Xenopus Oocytes by Atomic Absorption Spectrophotometry: An Alternative to Radioisotope Assays

Published on: February 19, 2013

Specific Binding of Rubidium in Chlorella.

D Cohen1

  • 1Department of Agriculture, University of Oxford, England.

The Journal of General Physiology
|October 30, 2009
PubMed
Summary

Researchers identified specific binding sites for potassium (K) in Chlorella by examining rubidium (Rb) uptake. These sites exhibit selective affinity for ions with a specific crystalline radius and high polarizability, crucial for active transport mechanisms.

Area of Science:

  • Plant Physiology
  • Biochemistry
  • Ion Transport

Background:

  • Chlorella utilizes active transport for potassium (K) uptake.
  • Specific binding sites are hypothesized to be involved in this K+ transport mechanism.

Purpose of the Study:

  • To characterize the specific binding sites for potassium in Chlorella.
  • To determine the ion binding properties and affinities of these sites.

Main Methods:

  • Utilized rubidium-86 (Rb(86)) as a tracer to study potassium binding sites.
  • Measured Rb(86) uptake and displacement by various ions at different concentrations.
  • Assessed ion affinity by determining the concentration required for 50% displacement of Rb(86).
  • Investigated the effect of cell treatment (freezing, boiling) on ion affinity.

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Main Results:

  • Identified heterogeneous binding sites for potassium (K) in Chlorella.
  • Determined the order of ion affinity for these sites, which remained consistent after cell treatments.
  • Found that affinity is maximal for ions with a crystalline radius of 1.3–1.5 Å and high polarizability.
  • Observed that affinity is not correlated with hydrated radius or valency.

Conclusions:

  • The specific binding sites for potassium (K) in Chlorella exhibit selectivity based on ion size and polarizability, not hydrated radius or charge.
  • The structural arrangement of binding groups within the site favors ions with specific diameters (2.6–3.0 Å) and high polarizability.
  • These findings provide insights into the molecular basis of active potassium transport in plant cells.