Identification of sulphur-rich proteins which resist rumen degradation and are hydrolysed rapidly by intestinal proteases.
Several proteins with high proportions of S-containing essential amino acids were incubated in sheep rumen fluid in vitro and their rate of digestion was examined by sodium dodecyl sulphate-polyacrylamide-gel electrophoresis. The S-rich proteins rice prolamin (10 kDa), maize zein (10 kDa) and the 3.2 kDa pumpkin (Cucurbita maxima L.) trypsin inhibitor-1 (CMTI-1) were highly resistant to rumen fluid degradation, relative to control proteins of known degradation rate (casein, bovine serum albumin (BSA) and pea (Pisum sativum) albumin-1 (PA1)). Comparison of PA1 and a recombinant N-terminal epitope-tagged PA1 indicated that addition of the epitope caused a slight increase in resistance to rumen degradation. The proteins were also incubated with a mixture of trypsin (EC 3.4.21.4) and chymotrypsin (EC 3.4.21.1). PA1, BSA and casein were hydrolysed less rapidly than rice prolamin, maize zein and CMTI-1. Digestion by these intestinal proteases appeared to be complete. Thus, the prolamin, zein and CMTI-1 proteins are suitable candidates for expression as foreign proteins in pasture plants to increase throughput and uptake of essential amino acids in sheep.
Hancock
K R
KR
Plant Molecular Genetics Laboratory, New Zealand Pastoral Agriculture Research Institute, Palmerston North.
Ealing
P M
PM
White
D W
DW
D000601:Amino Acids, Essential / Q000378:metabolism; D000818:Animals; D001483:Base Sequence; D004063:Digestion; D004591:Electrophoresis, Polyacrylamide Gel; D010450:Endopeptidases / Q000378:metabolism*; D066298:In Vitro Techniques; D008297:Male; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D055315:Prolamins; D012417:Rumen / Q000201:enzymology*; D012756:Sheep; D014361:Trypsin Inhibitors / Q000378:metabolism; D015028:Zein / Q000378:metabolism
D000601:Amino Acids, Essential; C081870:CMTI protein, Cucurbita maxima; D010940:Plant Proteins; D055315:Prolamins; D014361:Trypsin Inhibitors; D015028:Zein; D010450:Endopeptidases