Studies on the entry of fructose-2,6-bisphosphate into chloroplasts.

Autor: Smeekens S; Division of Molecular Plant Biology, University of California, Hilgard Hall, Berkeley California 94720., Macdonald FD, Buchanan BB
Jazyk: angličtina
Zdroj: Plant physiology [Plant Physiol] 1989 Apr; Vol. 89 (4), pp. 1270-4.
DOI: 10.1104/pp.89.4.1270
Abstrakt: The regulatory metabolite fructose-2,6-bisphosphate (Fru-2,6-P(2)) has an important function in controlling the intermediary carbon metabolism of leaves. Fru-2,6-P(2) controls two cytosolic enzymes involved in the interconversion of fructose-6-phosphate and fructose-1,6-bisphosphate (fructose-1,6-bisphosphatase and pyrophosphate, fructose-6-phosphate 1-phosphotransferase) and thereby controls the partitioning of photosynthate between sucrose and starch. It has been demonstrated that Fru-2,6-P(2) is present mainly in the cytosol. Here we present evidence that Fru-2,6-P(2) can be taken up by isolated intact chloroplasts but at a very slow rate (about 0.01 micromoles per milligram of chlorophyll per hour). This uptake is time and concentration dependent and is inhibited by PPi. When provided a physiological concentration of Fru-2,6-P(2) (10 micromolar), chloroplasts accumulated up to 0.6 micromolar Fru-2,6-P(2) in the stroma. Elevated plastid Fru-2,6-P(2) levels had no effect on overall photosynthetic rates of isolated chloroplasts. The results indicate that, while Fru-2,6-P(2) enters isolated chloroplasts at a sluggish rate, caution should be exercised in ascribing physiological importance to effects of Fru-2,6-P(2) on chloroplast enzymes.
Databáze: MEDLINE