Methods of Comparing Amino Acid Composition of Proteins: Application to Undigested Proteins in the Preruminant Calf

Abstract

The digestive utilization of dietary proteins at different sites along the digestive tract and the effects of their ingestion on the function of the digestive tract (secretion of endogenous proteins, development of microflora) can be inferred from the proportions of dietary, endogenous or microbial proteins. A first approach was to examine the proportions of some characteristic amino acids. A more accurate interpretation could be made by studying the additional undigested protein provided by the ingestion of an ‘experimental’ diet whose composition was calculated, for example, with regard to the undigested protein obtained with a very digestible diet (milk in the calf). These interpretations were often insufficient and did not extract all of the possible information. Thus, more global methods with statistical criterions had to be used. Some allowed two proteins (correlation and linear regression, average relative difference, χ²) to be compared. Others made it possible to take many proteins into consideration (factorial correspondence analysis). Finally, examples were given to seek the respective proportions of many proteins in a complex mixture or to estimate the most probable amino acid composition of the ‘microbial + endogenous’ proteins which escaped digestion in the small intestine. These various approaches have been discussed, with examples taken from our experimental results obtained in the preruminant calf, to show their advantages and limitations. In any case, the quality of the interpretation depends on the quality of the available results on the amino acid composition of endogenous, microbial and undigested dietary proteins.

Estimation of ileal output of gastro-intestinal glycoprotein in weaned piglets using three different methods

“…Since the ELISA intra-and inter-plate variabilities were close between these two studies, it seems that the present ELISA was more variable, possibly due to the higher complexity of the piglet, as compared to the preruminant calf ileal digesta, but also to larger animal variations. By contrast, the two other methods provided more limited individual variability, twice lower as that for bovine glycoprotein ELISA [20] but four-folds lower than the present ELISA. Whether this can be related to the fact they are also less specific than ELISA, and therefore contribute to level individual variability, raises the question of the actual biological variability of glycoprotein ileal concentration and outputs.…”

“…Tryptophan, which is destroyed by acid hydrolysis, was not analyzed. Amino acid composition of the purified glycoprotein was compared to published amino acid compositions of mucin from different animal species by the χ 2 distance as previously described by Guilloteau et al [20]. The lower the χ 2 distance, the higher the similarity between the compared proteins.…”

A new method of estimating the proportions of different proteins in a mixture using amino acid profiles: application to undigested proteins in the preruminant calf

“…The method described herein for obtaining the &dquo;best fit&dquo; mixture is based on simple rules for the determination of compositions of mixtures, associated with a calculation which allows 2 proteins to be compared taking into account all the differences between their amino acid compositions (distance of X 2 ) (Guilloteau et al, 1983). The mathematical procedure is mainly a multiple regression analysis which minimizes the residual sum of squares (Williams, 1959 (Guilloteau ef al, 1986)).…”

“…For this purpose, let us consider another method described by Guilloteau et al (1983) and which minimizes the distance of x 2 .…”

“…However, this method is inaccurate and it appears to be more interesting to take into account the full spectrum of amino acids as proposed by Evans et al (1975), Patureau-Mirand et al (1977) and Guilloteau et al (1983). The aim of this work was to improve the previous procedures by devising a mathematical model which establishes in what theoretical proportions reference proteins (ie dietary, endogenous and bacterial) should be mixed to produce the overall amino acid composition the most similar to that found in composite digesta.…”