Mechanistic Investigation of a Starch-Branching Enzyme Using Hydrodynamic Volume SEC Analysis

Transfer to Polymer and Long-Chain Branching in PLP-SEC of Acrylates

Pulsed laser polymerization (PLP) combined with size exclusion chromatography (SEC) is the method of choice for determining propagation rate coefficients. The influence of the long-chain branching in PLP-SEC is investigated using multiple-detection SEC and a recently developed method to detect long-chain branching [P. Castignolles, R. Grab, M. Parkinson, M. Wilhelm, M. Gaborieau, Polymer 2009, 50, 2373.] While little or no long-chain branching is detected in poly(n-butyl acrylate), the error in relevant molecular weights of poly(2-ethylhexyl acrylate) is large (30-100%) due to long-chain branching. Possible variations of propagation rate coefficient with alkyl groups in alkyl acrylates or with the solvent have to be reconsidered.

Proteins from multiple metabolic pathways associate with starch biosynthetic enzymes in high molecular weight complexes: a model for regulation of carbon allocation in maize amyloplasts

Starch biosynthetic enzymes from maize (Zea mays) and wheat (Triticum aestivum) amyloplasts exist in cell extracts in high molecular weight complexes; however, the nature of those assemblies remains to be defined. This study tested the interdependence of the maize enzymes starch synthase IIa (SSIIa), SSIII, starch branching enzyme IIb (SBEIIb), and SBEIIa for assembly into multisubunit complexes. Mutations that eliminated any one of those proteins also prevented the others from assembling into a high molecular mass form of approximately 670 kD, so that SSIII, SSIIa, SBEIIa, and SBEIIb most likely all exist together in the same complex. SSIIa, SBEIIb, and SBEIIa, but not SSIII, were also interdependent for assembly into a complex of approximately 300 kD. SSIII, SSIIa, SBEIIa, and SBEIIb copurified through successive chromatography steps, and SBEIIa, SBEIIb, and SSIIa coimmunoprecipitated with SSIII in a phosphorylation-dependent manner. SBEIIa and SBEIIb also were retained on an affinity column bearing a specific conserved fragment of SSIII located outside of the SS catalytic domain. Additional proteins that copurified with SSIII in multiple biochemical methods included the two known isoforms of pyruvate orthophosphate dikinase (PPDK), large and small subunits of ADP-glucose pyrophosphorylase, and the sucrose synthase isoform SUS-SH1. PPDK and SUS-SH1 required SSIII, SSIIa, SBEIIa, and SBEIIb for assembly into the 670-kD complex. These complexes may function in global regulation of carbon partitioning between metabolic pathways in developing seeds.

Toward a full characterization of native starch: separation and detection by size-exclusion chromatography

The structure of starch molecules is relevant to nutrition and industrial applications. Size-exclusion chromatography (SEC, also known as GPC) of native starch generally suffers non-satisfactory repeatability and reproducibility of the dissolution and separation. This work combines two polar organic solvents: dimethylsulfoxide for complete dissolution and dimethylacetamide to limit shear degradation. The separation is as repeatable as that of polystyrene standards performing dissolution and separation at 80 degrees C. Successful covalent-labeling on the glucose unit is claimed to be published here for the first time in non-degradative conditions and allows the use of UV detector with significantly higher sensitivity than with a refractometer.