(F.L., I.J.T., M.J.E.)Mutations affecting specific starch biosynthetic enzymes commonly have pleiotropic effects on other enzymes in the same metabolic pathway. Such genetic evidence indicates functional relationships between components of the starch biosynthetic system, including starch synthases (SSs), starch branching enzymes (BEs), and starch debranching enzymes; however, the molecular explanation for these functional interactions is not known. One possibility is that specific SSs, BEs, and/or starch debranching enzymes associate physically with each other in multisubunit complexes. To test this hypothesis, this study sought to identify stable associations between three separate SS polypeptides (SSI, SSIIa, and SSIII) and three separate BE polypeptides (BEI, BEIIa, and BEIIb) from maize (Zea mays) amyloplasts. Detection methods included in vivo protein-protein interaction tests in yeast (Saccharomyces cerevisiae) nuclei, immunoprecipitation, and affinity purification using recombinant proteins as the solid phase ligand. Eight different instances were detected of specific pairs of proteins associating either directly or indirectly in the same multisubunit complex, and direct, pairwise interactions were indicated by the in vivo test in yeast. In addition, SSIIa, SSIII, BEIIa, and BEIIb all comigrated in gel permeation chromatography in a high molecular mass form of approximately 600 kD, and SSIIa, BEIIa, and BEIIb also migrated in a second high molecular form, lacking SSIII, of approximately 300 kD. Monomer forms of all four proteins were also detected by gel permeation chromatography. The 600-and 300-kD complexes were stable at high salt concentration, suggesting that hydrophobic effects are involved in the association between subunits.Plant species typically store reduced carbon in the glucan polymer amylopectin, located in semicrystalline, insoluble starch granules. Amylopectin has the same chemical nature as glycogen, the soluble glucan storage polymer present in most nonplant species. Glc residues in both polymers are linked in linear chains by a-(1/4) glycoside bonds, and these are joined by a-(1/6) glycoside bonds referred to as branch linkages. Amylopectin and glycogen differ in molecular architecture, however, with regard to branch frequency and the relative positions of the a-(1/6) bonds. Branch linkages of amylopectin are located in clusters relatively close to one another compared to the longer interbranch distances of glycogen (Thompson, 2000). Also, the branch frequency is lower in amylopectin than glycogen. These architectural features likely allow amylopectin crystallization and thus explain the different physical properties of starch and glycogen.The chemical structures of amylopectin and glycogen are produced by the same classes of enzyme, specifically a glucan synthase that transfers Glc residues to a growing linear chain from a nucleotide sugar donor and a glucan branching enzyme that cleaves a linear chain at a glycoside bond and transfers one portion of it to a C-6 hydroxyl. A possible ex...
This chapter describes a new perspective on student learning and its impact on the act and art of college teaching. It also addresses the teaching role of student affairs professionals.
β-Carotene oxygenase 2 cleaves β-carotene asymmetrically at non-central double bonds of the polyene chain, yielding apocarotenal molecules. The hypothesis tested was that apocarotenoids are able to stimulate transcription by activating retinoic acid receptors (RARs). The effects of long- and short-chain apocarotenals and apocarotenoic acids on the activation of RARα and RARβ transfected into monkey kidney fibroblast cells (CV-1) were investigated. We synthesized or purified β-apo-8′-carotenoic acid (apo-8′-CA), β-apo-14′-carotenoic acid (apo-14′-CA), β-cyclocitral (BCL), β-cyclogernanic acid (BCA), β-ionone (BI), β-ionylideneacetaldehyde (BIA) β-ionylideneacetic acid (BIAA) and a C13 ketone, β-apo-13-carotenone (C13). None of the apocarotenoids tested showed significant transactivation activity for the RARs when compared with all-trans retinoic acid (RA). The results suggest that biological effects of these apocarotenoids are through mechanisms other than activation of RARα and β.
The past two decades have ushered changes regarding the national science curriculum for K-12 students. Focusing on gifted and talented (GT) students, the literature reveals they clamor for unique experiences in constructing their knowledge in science education. This chapter explores science instruction for GT in this digital age using a Makerspace learning environment. Guided by the tenets of the Next Generation Science Standards, this chapter is supported by outlined standards and objectives connecting science content to GT learners' unique needs. The theory of socialization, specifically cognitive development coupled with the theory of constructivism, was used to ground this chapter. Results show Makerspace learning environments where GT students are exposed to inductive strategies and yield a greater return on student learning investments compared to the traditional deductive science classroom environment.
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