The Cyanelles (Organelles of a Low Evolutionary Scale) Possess a Phosphate‐Translocator and a Glucose‐Carrier in Cyanophora paradoxa

Abstract

Cyanelles from Cyanophora paradoxa can easily be isolated and assayed for their carrier composition by the silicone oil filtering technique. The present investigation demonstrates a Pi‐translocator transferring phosphate, dihydroxyacetone phosphate and 3‐phosphoglycerate in a counter exchange mode in cyanelles as in chloroplasts of higher plants. The uptake of Pi is inhibited by dihydroxyacetone phosphate, phosphoglycerate and glucose‐6‐P, only poorly by phosphoenolpyruvate and not by 2‐phosphoglycerate. The inhibitors pyridoxalphosphate and 4,4′diisothiocyanostilbene‐2,2K'disulfonic acid at low concentration also affect Pi‐uptake. Cyanelles probably transport photosynthate (reductant and ATP) by triosephosphates. This is the first demonstration of a phosphate translocator in an organism of a low evolutionary scale. Cyanelles also transport glucose which proceeds in two phases. In the lower concentration range (≤ 2.5 mM), glucose penetrates by facilitated diffusion, whereas transport follows first‐order kinetics at higher amounts (> 2.5 mM). In the low concentration range, glucose‐transport is affected by high concentrations of 3‐O‐methylglucose and fructose. The physiological role of the glucose‐transport carrier in Cyanophora is doubtful. It may function in transporting glucose into cyanelles if the carbon level inside them becomes limiting, e.g. in dark periods.

In vitro import of pre‐ferredoxin‐NADP+‐oxidoreductase from Cyanophora paradoxa into cyanelles and into pea chloroplasts

“…Only the internalized and processed mature FNR was protected, regardless if additional thermolysin treatment took place. Data from metabolite exchange studies [10,14] made it possible to simulate a 'cytosolic' environment for cyanelles during the isolation steps and to establish genuine in vitro conditions. Using BSM, cyanelles could be held stable for several hours.…”

The Transition from Glycogen to Starch Metabolism in Cyanobacteria and Eukaryotes

“…This transport is in fact an exchange reaction between glucose-6-P and orthophosphate. This type of transport had been previously demonstrated to operate on purified Cyanophora paradoxa muroplasts (Schlichting and Bothe 1993). The UhpC gene was acquired by all three Archaeplastida clades, and displays a monophyletic origin in Archaeplastida.…”

Single, Ancient Origin of a Plastid Metabolite Translocator Family in Plantae from an Endomembrane-Derived Ancestor

“…Although we do not have glaucophyte translocators in the tree, the signature activity of plastidic phosphate translocators has been detected in isolated cyanelles of Cyanophora paradoxa, indicating the presence of plastidic phosphate translocators (21). We therefore hypothesize that the insertion of a phosphate translocator into the plasma membrane of the endosymbiont occurred before the split of the Plantae and was probably a critical step in rendering the association between the cyanobacterium and the mitochondriate eukaryote irreversible.…”