Formation of thermally induced aggregates of the soya globulin beta-conglycinin.
The effect of ionic strength (I) on the formation of thermally induced aggregates by the 7S globular storage protein of soya, beta-conglycinin, has been studied using atomic force microscopy. Aggregates were only apparent when I> or =0.1, and had a fibrous appearance, with a height (diameter) of 8-11 nm. At high ionic strength (I=1.0) the aggregates appeared to associate into clumps. When aggregate formation was studied at I=0.2, it was clear that aggregation only began at temperatures above the main thermal transition for the protein at 75 degrees C, as determined by differential scanning calorimetry. This coincided with a small change in secondary structure, as indicated by circular dichroism spectroscopy, suggesting that a degree of unfolding was necessary for aggregation to proceed. Despite prolonged heating the size of the aggregates did not increase indefinitely, suggesting that certain beta-conglycinin isoforms were able to act as chain terminators. At higher protein concentrations (1% w/v) the linear aggregates appeared to form large macroaggregates, which may be the precursors of protein gel formation. The ability of beta-conglycinin to form such distinctive aggregates is discussed in relation to the presence of acidic inserts in certain of the beta-conglycinin subunits, which may play an important role in limiting aggregate length.
Mills
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EN
Institute of Food Research, Norwich Research Park, Colney, NR4 7UA, Norwich, UK. clare.mills@bbsrc.ac.uk
Huang
L
L
Noel
T R
TR
Gunning
A P
AP
Morris
V J
VJ
D006358:Hot Temperature; D018625:Microscopy, Atomic Force; D009994:Osmolar Concentration; D010316:Particle Size; D011108:Polymers / Q000737:chemistry; D017433:Protein Structure, Secondary; D030262:Soybean Proteins / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D013696:Temperature
D011108:Polymers; D030262:Soybean Proteins