Related Experiment Video
Updated: Aug 8, 2026

Loading a Calcium Dye into Frog Nerve Endings Through the Nerve Stump: Calcium Transient Registration in the Frog Neuromuscular Junction
Published on: July 8, 2017
An Autoinhibitory Substance Produced by Platydorina caudata Kofoid
1Department of Botany, University of Kentucky, Lexington, Kentucky 40506.
Abstract:
An inhibitory substance was obtained from culture filtrates of Platydorina caudata Kofoid, (a colonial, green flagellate), in which death of the culture had occurred. The cessation of growth occurs before, and is seemingly independent of, medium depletion. The substance can be detected as early as the 15th day, and by the 25th day growth is completely suppressed. A bioassay method for quantitating the activity of the substance was devised. The substance is heat-labile, nondialyzable, acid-labile, and apparently specific for Platydorina. The substance resists short periods of freezing and bacterial contamination. Preliminary results suggest that trypsin destroys activity of the substance.
Related Concept Videos
Feedback Inhibition
Feedback Regulation of Calcium Concentration
Various transmembrane receptors, such as G protein-coupled receptors (GPCRs), elicit a response to extracellular signals by increasing cytosolic calcium. Activated GPCRs...
Ligand-Gated Ion Channel Receptor: Gating Mechanism
Calmodulin-dependent Signaling
The Ca2+-CaM complex does not have enzymatic activity by itself. Instead, the complex binds downstream target proteins, including membrane proteins or enzymes,...
Indirect-Acting Cholinergic Agonists: Mechanism of Action
Reversible inhibitors like edrophonium bind to a specific part of the enzyme called the anionic catalytic site. They form noncovalent bonds, which means they are not strongly attached to the enzyme. This creates a temporary and less stable enzyme–inhibitor complex, leading to...
Resting Membrane Potential
The Inside of a Neuron is More Negative
The membrane potential of a cell can be measured by inserting a microelectrode into a cell and comparing the charge to a reference electrode in the extracellular fluid. The...

