Failure to corroborate claims that the developing endosperm of wheat (Triticum aestivum) contains significant activities of fructose-1,6-bisphosphatase.

This work was done to test claims (Sangwan and Singh, Physiol. Plant. 73: 21-26) that the developing endosperm of wheat (Triticum aestivum L.) contains a cytosolic and a plastidic fructose- 1,6-bisphosphatase (EC 3.1.3.11; FBPase). Repetition of the procedure of Sangwan and Singh with extracts of developing endosperm of Triticum aestivum cv. Mercia produced two peaks of apparent FBPase activity on elution from DEAE-cellulose. Both peaks showed high activity of pyrophosphate:fructose-6-phos-phate 1-phosphotransferase [EC 2.7.1.90; PFK(PP(i) )]. The apparent FBPase activity in both peaks was stimulated by 20 μM fructose-2,6-bisphosphate and inhibited by antibodies to PFK(PP(i) ). Antibody to plastidic FBPase did not react positively in an immunoblot analysis with any protein of M(r) comparable to that of known FBPase in either peak. It is argued that the ability of each peak to convert fructose-1,6-bisphosphate to fructose-6-phosphate was due to PFK(PP(i) ). and that there remains no substantiated evidence for the presence of a plastidic FBPase in the developing endosperm of wheat.