Instituto Fitotecnico Santa Catalina (FCAyF, UNLP)


Electrophoretic studies on maize endosperm proteins: modifications to Laemmli´s SDS-Page technique --Corcuera1, VR, Bernatene2, E, Naranjo3, CA

1. Technician of CIC 2. Technician of CONICET 3. Researcher of CONICET

Laemmli´s SDS polyacrylamide gel electrophoresis is based on conditions that assure protein dissociation into their individual polypeptides, minimizing the risk of their aggregation. Electrophoresis is then run, in a discontinuous buffer system using a running buffer with a different pH than the one used to prepare the stacking and resolving gels. These systems were originally developed by Ornstein (1964) and Davis (1964). In our laboratory, electrophoretic studies on maize endosperm proteins were carried out using a Hoeffer Vertical Slab Unit SE 600 and a power source Hoeffer Mighty Slim SX 250. The modifications suggested to the original Laemmli´s technique are listed below:

A. Maize endosperms have to be milled to 100 mesh and the flours defatted with n-hexane using a ratio 1:10 (sample:solvent) at 4 C and stirring during one hour.

B. Several sample:buffer ratios were tested. The ratios examined were 40 mg flour:1000 uL buffer, 70:1000 and 100:1000.

C. Proteins were extracted from meal for 2, 6, 12 and 24 hours at room temperature using SDS-extraction buffer prepared as follows: 18.0 ml water + 7.65 ml 3x buffer + 1.35 ml 2-ME. The 3x buffer contained: 6.25 ml Tris HCl (ph: 6.8) + 12.05 ml tap water + 2.0 g SDS + 10.0 mg gamma pironine + 10.0 ml glycerol. During the extraction time, the samples were vortexed periodically.

D. Protein extracts were heated in boiling water for 10 minutes with later cooling under water flow up to room temperature.

E. The extracts were clarified by centrifugation for 10, 12 or 15 minutes at 12,500 - 13,000 and 14,000 x G.

F. 10 and 12% gels were used, so different monomer concentrations (%T) were analyzed.

G. 50 uL of each extract were loaded onto each lane of the gels. Electrophoresis was run at constant current and variable voltage (20 to 35 ampere/gel).

H. Bands were fixed using a mixture containing 440 ml tap water + 35 ml acetic acid + 25 ml methanol during 3 hours using a shaker. Later on, gel staining was done using a mixture of 500 mg Coomasie Blue R + 250 ml methanol + 200 ml tap water + 50 ml acetic acid during 3 hours using a shaker. Finally, gel decolouring was done employing a mixture of 335 ml tap water + 40 ml acetic acid +125 ml ethanol during 3 to 4 hours using a shaker and with constant changes of the mixture. Between each step, the gels were washed three times with deionized water.

After testing all the modifications listed above, it can be said that for maize endosperm proteins, the best electrophoretic results are obtained using the following procedures:

1. Better results are obtained using fine milling and defatted endosperm flours.

2. The best sample:buffer ratio was 70:1000. When 100:1000 ratio was used, the bands heaped upon themselves producing spots and changing the electrophoretic pattern.

3. The best extracts were obtained after 24 hours extraction, shaking 4 times in a vortex 40 minutes each within the period.

4. Better results are obtained using 12% gels, as they give better definition of the bands. 10% gels are not suitable as some bands do not appear and others join amongst themselves looking like spots or single bands.

5. Better results are also obtained centrifugating 15 minutes at 14,000 x G to clarify the extracts.

The maize samples used belong to different types of endosperm: flint, opaque-2 and waxy. When SDS-PAGE was run according to the above procedures, 19 bands could be observed. The electrophoretic pattern varied with the maize type. Flint maizes present all the bands except band thirteen. Bands 1,2,3,5,6 and 18 are absent in waxy and opaque-2 materials. On the other hand, band 16 is absent in opaque-2 maizes and band 14 was not observed in waxy maizes. It can be said that polypeptide electrophoretic pattern is suitable to differentiate amongst groups of maize with different endosperm natures, though it does not allow distinguishing phenotypes within the group. For this purpose, protein fractionation must be done.

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.

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