Oleosins (24 and 18 kDa) are hydrolyzed not only in extracted soybean oil bodies but also in soybean germination.
After oil bodies (OBs) were extracted from ungerminated soybean by pH 6.8 extraction, it was found that 24 and 18 kDa oleosins were hydrolyzed in the extracted OBs, which contained many OB extrinsic proteins (i.e., lipoxygenase, β-conglycinin, γ-conglycinin, β-amylase, glycinin, Gly m Bd 30K (Bd 30K), and P34 probable thiol protease (P34)) as well as OB intrinsic proteins. In this study, some properties (specificity, optimal pH and temperature) of the proteases of 24 and 18 kDa oleosins and the oleosin hydrolysis in soybean germination were examined, and the high relationship between Bd 30K/P34 and the proteases was also discussed. The results showed (1) the proteases were OB extrinsic proteins, which had high specificity to hydrolyze 24 and 18 kDa oleosins, and cleaved the specific peptide bonds to form limited hydrolyzed products; (2) 24 and 18 kDa oleosins were not hydrolyzed in the absence of Bd 30K and P34 (or some Tricine-SDS-PAGE undetectable proteins); (3) the protease of 24 kDa oleosin had strong resistance to alkaline pH while that of 18 kDa oleosin had weak resistance to alkaline pH, and Bd 30K and P34, resolved into two spots on two-dimensional electrophoresis gel, also showed the same trend; (4) 16 kDa oleosin as well as 24 and 18 kDa oleosins were hydrolyzed in soybean germination, and Bd 30K and P34 were always contained in the extracted OBs from germinated soybean even when all oleosins were hydrolyzed; (5) the optimal temperature and pH of the proteases were respectively determined as in the ranges of 35-50 °C and pH 6.0-6.5, while 60 °C or pH 11.0 could denature them.
State Key Laboratory of Food Science and Technology, Synergetic Innovation Center of Food Safety and Nutrition, School of Food Science and Technology, Jiangnan University , 1800 Lihu Avenue, Wuxi, Jiangsu Province 214122, PR China.
Yeming
Y
Chen
Luping
L
Zhao
Yanyun
Y
Cao
Xiangzhen
X
Kong
Yufei
Y
Hua
D018525:Germination; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D008565:Membrane Proteins / Q000378:metabolism*; D015388:Organelles / Q000378:metabolism*; D010447:Peptide Hydrolases / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism*; D012639:Seeds / Q000254:growth & development / Q000378:metabolism / Q000648:ultrastructure*; D013025:Glycine max / Q000648:ultrastructure*; D013696:Temperature
D008565:Membrane Proteins; D010940:Plant Proteins; C079299:oleosin 24 protein, Glycine max; D010447:Peptide Hydrolases