Carbohydrate Polymerc 16 (1991) 1-15 The Molecular Weight Distribution and Conformation of Citrus Pectinsin Solution Studiedby Hydrodynamics Stephen E. Harding,o* Gisela Berth,'Abigail Ball,o John R. Mitchello & Jose Garcia de la Torre' 'Department of Applied Biochemistry & Food Science, University of Nottingham, SuttonBonington LE12 5RD, UK 'Akademie der Wissenschaften der DDR, Zentralinstitut fiir Erndhrung, Potsdam-Rehbriicke, FRG 'Departamento de Quimica Fisica, Facultad de Ciencas, Universidad de Murcia, 30100 Murcia, Spain (Received 24 May 1990;accepted 4 July 1990) ABSTRACT The molecular weightdistribution of a citruspectin has beenanalysed by a combined approach using gel-permeationchromatography with low- speedsedimentation equilibrium. (l) A pectin preparation from citrus fruit was fractionated on Sepharose CL-2BlSepharose CL-48. (2) Weight average molecular weights of the fractions weredetermined by low speed sedimentation equilibrium in multichannel cells.(3)An absolute calibra- tion for the column for this material was therebydefined. @ The (log- normal) molecular weight distribution thus obtained is consistent with a weightaverage of (%0M! l}UD gf mol, obtained separately on unfrac- tionatedmateial, and consistent with a distibution obtainedon the same material but usinglight scatteing as the molecular weight probe. The conformation of the pectin fractions in solution was studied in terms of: (1) the Wales-Van Holde parameter, k,l[rt]; Q) Mark- Houwink-Kuhn-Sakurada plots of sedimentation coefficient and intrin- sic viscosity data versus molecular weight;(3) rod modelsand (4) worm- like-coil models. The sedimentationdata is consistent with a rod model (or a worm-like-coil with a large persistence length) with mass per unit length - 430g mol-t nm-t. The intrinsic viscosity data is also consislent with a rod model but showssome anomalous features which may be sug- gestive of worm-like-coil behaviour at higher molecular weight, although it is not possible to ft this data with a realistic valueof the mass per unit length. I *To whom correspondence should beaddressed. Carbohyd.rate Polymers 0144-8617 191/503.50 - @ 1991Elsevier Science publishers Ltd, England. Printed in Great Britain