|Abstract or Summary
- Investigations were conducted to determine the nature, type,
functional properties and the amounts of different proteins found in
bovine rumen tissue.
Data concerning the effect of pH and salt concentration on
the extractability of proteins from rumen tissue indicated that 92%
of the proteins could be extracted in aqueous solutions at either pH
3.0 or 10.0. Rumen tissue proteins showed the least solubility in
the pH range of 5 to 6. Two protein isolates having distinct compositional
differences were obtained from the pH 10.0 aqueous
extract by successively lowering the pH to 7.0 and 5.4. The
supernatant remaining from the isoelectric precipitation at pH 5.4
contained one major sodium dodecyl sulfate (SDS) gel electrophoretic
band corresponding to a subunit molecular weight of 67,000. However,
bands corresponding to the four major contractile proteins
were not detected.
SDS-gel electrophoresis was used to identify the proteins in
fresh rumen tissue, in the various extracts and in the protein
isolates. The gels were subjected to densitometric analysis to
obtain an estimate of the contractile proteins contained in the various
samples. The protein isolate obtained at an isoelectric precipitation
of pH 7.0 contained 28% myosin, 65% actin and 7% unidentified
proteins but no troponin or tropomyosin. The isolate obtained at
pH 5.4 contained 20% myosin, 40% actin, 19% troponin, 11% tropomyosin
and 10% unidentified proteins. The protein extract at pH 10.0
contained 12% myosin, 35% actin, 9.5% troponin, 13% tropomyosin
and 30.5% unidentified proteins. Based on 92% protein extractability
at pH 10.0 and assuming only the stroma proteins to be insoluble at
this pH, the protein composition of the fresh bovine rumen tissue
was calculated to be 11% myosin, 32% actin, 9% troponin, 12%
tropomyosin, 8% stroma, and 28% unidentified proteins. When the
rumen tissue was homogenized in distilled water at neutral pH, 5%
of the total soluble protein was myosin, 45% actin, 22% troponin and
20% tropomyosin. However, once the contractile proteins of the
rumen tissue were purified, their solubility properties were similar
to those of skeletal muscle contractile proteins.
Contractile proteins purified from rumen and skeletal muscle
yielded identical R [subscript m] values on SDS gel electrophoresis, and their
estimated molecular weights were similar. Myosin from both rumen and skeletal muscle gave similar elution patterns on DEAE Sephadex A-50 columns. In each case, the major myosin peak emerged at a
KC1 concentration of about 0.1 M.
The ATPase activity of rumen myosin was lower at low ionic
strengths but higher at high ionic strengths than that of skeletal
myosin. The activity of both types of myosin was stimulated by Ca⁺⁺
and EDTA but inhibited by Mg⁺⁺.
Amino acid analysis of rumen and skeletal myosins were
similar, although rumen myosin had lower levels of lysine, aspartic
acid, isoleucine, leucine and phenylalanine, and higher levels of
glycine, valine, methionine and tyrosine, than skeletal myosin.
Rumen and skeletal actin differed somewhat in amino acid composition.
The most notable differences were the higher contents of
glutamic acid and lysine in the rumen actin.
The emulsifying capacity of the two rumen protein isolates
were about 30% lower than that of the skeletal muscle proteins.
However, the rumen protein isolates showed excellent stability and
consistency which were judged to be comparable to those of skeletal
Rumen protein extracts and isolates showed excellent
whippability and foam stability characteristics that were found to be
equivalent to dried, reconstituted egg albumen.