Pectin microgels and their subunit structure.

High-performance size exclusion chromatography revealed that alkaline-extracted peach fruit pectin dissolved in 0.05 M NaNO3 comprised a hierarchy of at least four aggregated, macromolecular-sized species. Each of the three largest species was found to be comparable in length to the three smallest subunits of an interconnecting gel network visualized by transmission electron microscopy of pectin, rapidly dried from solution. The interconnecting subunits of the gel network were rods or segmented rods and the integrated network formed a circular gel about 1 micron in diameter. Shadowed samples prepared from 5 and 50 mM NaCl or aqueous glycerol solutions produced images of partially dissociated subunits.

Macromolecular components of tomato fruit pectin.

Chelate and alkaline-soluble pectin extracted from cell walls of pericarp tissue from mature green, turning, and red ripe (Lycopersicon esculentum Mill.) fruit (cv. Rutgers), were studied by high-performance size-exclusion chromatography. Computer-aided curve fitting of the chromatograms to a series of Gaussian-shaped components revealed that pectin from all fractions was composed of a linear combination of five macromolecular-sized species. The relative sizes of these macromolecules as obtained from their radii of gyration were 1:2:4:8:16. Dialysis against 0.05 M NaCl induced partial dissociation of the biopolymers. Apparently, the weight fraction of smaller sized species increased at the expense of larger ones. Also, the dissociation produced low-molecular-weight fragments. Behavior in the presence of 0.05 M NaCl led to the conclusion that cell wall pectin acted as if it were an aggregated mosaic, held together at least partially through noncovalent interactions.

Preparative liquid chromatography of carbohydrates: mono- and di-saccharides, uronic acids, and related derivatives.

The general principles and practical aspects of preparative high-performance liquid chromatography (l.c.) of mono- and di-saccharides, sugars acids, lactones, and N-acetylated amino sugar derivatives are described. Milligram to gram quantities of these carbohydrates were isolated on semi-preparative (0.78 X 30 cm) or preparative (approximately 2.0 X 30 cm) columns packed with aminopropyl silica gel provided better resolution of individual mono- and di-saccharides, but columns of cation-exchange resin had higher capacity and were more durable and economical to use. Preparative, cation-exchange columns were operated at flow rates of less than 5 mL/min and pressures of approximately 1-2 MPa, allowing them to be used on unmodified analytical l.c. systems. Details are given for the efficient packing, use, and care of these columns, and on the effects of column selectivity, packing technique, and sample size on chromatographic resolution. Isolation of naturally occurring sugars from biological sources on a laboratory-packed column is described.