Compartmentation of the starch-related R1 protein in higher plants
2000
Ritte, G. | Eckermann, N. | Haebel, S. | Lorberth, R. | Steup, M.
Starch granules were isolated from tubers or leaves of Solanum tuberosum L. and the starch associated proteins were analysed. Based on the solubilisation procedure used, two protein fractions were distinguished: Proteins that are bound to the surface of the starch particles and those enclosed within the granule. A 160 kDa starch associated protein was recovered in both fractions: in starch granule preparations isolated from darkened potato leaves it was predominantly located at the surface of the particle but in tuber starch it was mainly enclosed. In addition, the 160 kDa protein also occurs in a soluble state and resides in the stromal space of amyloplasts from tubers. By using matrix-assisted laser desorption/ionisation massspectrometry (MALDI-MS) the 160 kDa protein was identified to be the recently described R1 that appears to be involved in phosphorylation and/or degradation of starch. In a screening approach, starch granules and soluble proteins from tubers, seeds and fruits of a variety of plant species were analysed for R1 and the amount of phosphate covalently bound to starch was determined. The level of R1 did not correlate with the content of starch derived phosphate.
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