Background: Starch is the major component of cereal yield, yet the biochemical regulation of its synthesis is poorly understood. Results: Starch branching enzyme IIb is phosphorylated at three sites by two Ca 2ϩ -dependent protein kinases. Conclusion: Two phosphorylation sites represent a general mechanism of control in plants, the third is cereal specific. Significance: Identification of post-translational regulatory mechanism offers possibilities for targeted manipulation of starch.

The metabolism of polyamines was studied in K+-dependent strains of Escherichia coli. When these stringent organisms were in a medium containing Na+ instead of K+, protein synthesis was arrested, but synthesis of ribonucleic acid continued as it would in a relaxed organism. The Na+ medium inhibited synthesis of spermidine and S-adenosylmethionine. However, the synthesis of putrescine was accelerated at least fiveto eightfold. Exogenous ornithine doubled even this rate of putrescine synthesis but did not increase the low level of putrescine synthesis in the K+ medium. In K+ or Na+ media, with or without 0.3 mm arginine, putrescine was derived almost entirely from ornithine via ornithine decarboxylase. Addition of spermidine (5 mM) to a Na+ culture markedly inhibited putrescine synthesis. The ornithine decarboxylase of an extract of a K+-dependent strain prepared at low ionic strength was separated from ribosomes, deoxyribonucleic acid, and associated polyamines by centrifugation, and from many ions by ultrafiltration and fractionation on Sephadex G-100. Addition of Na+ and K+ salts to 200 mm was markedly inhibitory. The combined reductions both in synthesis of the inhibitor spermidine and in intracellular ionic strength may explain the in vivo activation of this enzyme.