Amino starches synthesis

Because of the importance of ADPGlc synthetase for plant starch synthesis, efforts have been made to determine the structure of the enzyme and to relate catalytic and allosteric function to structure. The spinach leaf enzyme is composed of two subunits of 51 and 54 kd mass (5,6). The molecular mass of the native enzyme is 206,000 and presumably is a tetramer composed of two of each subunit. The subunits are antigenically dissimilar, exhibit different peptide patterns on HPLC after trypsin digestion and their N-terminal amino acid sequences are different (7). Thus it is likely that the peptide subunits are products of different genes. 

Kida T, Shibai H. Inhibition by hadacidin. duazomycin A. and other amino acid derivatives of de novo starch synthesis. Agric Biol Chem 1985 49 3231-3237. 

Schlesinger and Anderson (44) separated the isozymes on starch-gel and DEAE-cellulose at various times after 14C-amino acids were added to a culture of E. coli synthesizing alkaline phosphatase. They found that initially most of the counts appeared in isozyme I, but later they appeared mainly in isozymes II and III. In another experiment where only enough radioactive amino acid was added to allow for 5 min of synthesis of radioactive protein, they found that the label is initially found in isozymes I and II and later in isozymes II and III. These experiments establish that the monomers of isozyme I are precursors for isozymes II and III. 

Research had confirmed that no parent simazine residues were found in treated com plants, and additional data on the dissipation pathway of simazine needed to be developed. Research also indicated that triazines interfered with the photosynthetic process on susceptible growing weeds, as evidenced by the appearance of chlorotic leaves. Steps were undertaken to elucidate simazine s dissipation pathway and herbicidal mode of action. In Basel, Dr. Gast (1958) showed that the accumulation of starch by common coleus (Coleus blumei Benth.) plants was inhibited from treatment with 2-chloro-4,6-bis-(alkyl-amino)-triazines due to the inhibition of sugar synthesis. At the same time, Moreland et al. (1958) found weed control activity could be reduced by supplying carbohydrates to the plants through their leaves and that simazine was a strong inhibitor of the Hill reaction in photosynthesis. Exer (1958) found that triazines inhibited the Hill reaction as strongly as urea of the CMU (monuron) type. 

Because glyceraldehyde-3-phosphate and dihydroxyacetone phosphate are readily interconverted, these two molecules (referred to the triose phosphates) are both considered to be Calvin cycle products. The synthesis of triose phosphate is sometimes referred to as the C3 pathway. Plants that produce triose phosphates during photosynthesis are called C3 plants. Triose phosphate molecules are used by plant cells in such biosynthetic processes as the formation of polysaccharides, fatty acids, and amino acids. Initially, most triose phosphate is used in the synthesis of starch and sucrose (Figure 13A). The metabolism of each of these molecules is briefly discussed below. 

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