Effect of protein secondary structures in mixed feedstuff detected by Fourier transform infrared spectroscopy on ruminal protein degradation kinetics

The objective of this study was to investigate the relationship between the protein secondary structure and the protein rumen degradation kinetics and the protein fractions of mixed feedstuffs of soybean meal with distillers dried grains with solubles (DDGS) at five mixed ratios (DDGS to soybean meal: 100 : 0, 70 : 30, 50 : 50, 30 : 70, 0 : 100). The Fourier transform infrared (FTIR) as a novel and cheap approach was used to detect the protein secondary structure, and the in situ nylon bag method was used to measure degradation kinetics of protein. Protein fractions were classified based on the Cornell net carbohydrate protein system. The results showed that (1) with the increasing soybean meal rate, the ruminal degraded protein and fractions of PB1 and PB2 were changed, (2) a higher α-helix to β-sheet ratio could result in a higher ruminally degraded protein, lower PB3 and PC, and higher PB1 and PB2 fractions in the feedstuff. So, mixing processing changed the feedstuff protein molecular structure spectral feature, which could influence the rumen degradation kinetics and protein fractions. It was inferred that protein degradation rate in mixed feedstuff can be measured by FTIR.

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Secondary Structure Estimation of Proteins Using the Amide III Region of Fourier Transform Infrared Spectroscopy: Application to Analyze Calcium-Binding-Induced Structural Changes in Calsequestrin

Applied Spectroscopy ◽

10.1366/0003702944028065 ◽

1994 ◽

Vol 48 (11) ◽

pp. 1432-1441 ◽

Cited By ~ 128

Author(s):

Fen-Ni Fu ◽

Daniel B. Deoliveira ◽

William R. Trumble ◽

Hemanta K. Sarkar ◽

Bal Ram Singh

Keyword(s):

Fourier Transform ◽

Secondary Structure ◽

Calcium Binding ◽

Structural Changes ◽

Spectroscopic Method ◽

Spectral Feature ◽

Protein Secondary Structure ◽

Fourier Transform Infrared ◽

Helical Structure ◽

Α Helix

A Fourier transform infrared spectroscopic method has been developed to analyze protein secondary structure by employing the amide III spectral region (1350–1200 cm−1)· Benefits of using the amide III region have been shown to be substantial. The interference from the water vibration (∼1640 cm−1) in the amide I region can be avoided when one is using the amide III band; furthermore, the amide III region also presents a more characterized spectral feature which provides easily resolved and better defined bands for quantitative analysis. Estimates of secondary structure are accomplished with the use of Fourier self-deconvolution, second derivatization, and curve-fitting on original protein spectra. The secondary structure frequency windows (α-helix, 1328–1289 cm−1; unordered, 1288–1256 cm−1; and β-sheets, 1255–1224 cm−1) have been obtained, and estimates of secondary structural contents are consistent with X-ray crystallography data for model proteins and parallel results obtained with the use of the amide I region. We have further applied the analysis to the structural change of calsequestrin upon Ca2+ binding. Treatment of calsequestrin with 1 mM Ca2+ results in the formation of crystalline aggregates accompanied by a 10% increase in α-helical structure, which is consistent with previous results obtained by Raman spectroscopy. Thus the amide III region of protein IR spectra appears to be a valuable tool in estimating individual protein secondary structural contents.

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