, Volume 119, Issue 2, pp 113-124

Sieve-tube proteins from Cucurbita maxima

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The two main proteins from the phloem exudate of Cucurbita maxima Duchesne have been isolated by ammonium-sulfate precipitation, DEAE-cellulose chromatography, and gel filtration, and have been characterized. They comprise about 40% each of the total protein. The amino-acid composition of these two proteins has been determined. Both are highly basic with an IEP above 9.5. The smaller protein has a molecular weight of ca. 30000 as determined by analytical ultracentrifugation, gel filtration, and SDS polyacrylamide gel electrophoresis. It easily dimerizes to a form which appears to be the naturally occurring structure. The larger protein has a molecular weight of 116000 (ultracentrifugation, SDS polyacrylamide gel electrophoresis). This protein forms a gel in the absence of SH-protecting agents. Several minor proteins have been detected by polyacrylamide gel electrophoresis.

Some results of the present article are contained in the “Staatsexamensarbeit” of J. B. and in the thesis of C. W.