Physiological actions of taurine

Automated simultaneous determination of ammonia and total amino acids in ruminal fluid and in vitro media

THE JOURNAL OF BIOLOGICAL CHEMISTRY: The Biochemical Behavior of LeadL I. Influence of Calcium, Phosphorus, and Vitamin D on Lead in Blood and Bone

Essential fatty acids in growth and development

Methionine, cysteine, homocysteine, and taurine are the 4 common sulfur-containing amino acids, but only the first 2 are incorporated into proteins. Sulfur belongs to the same group in the periodic table as oxygen but is much less electronegative. This difference accounts for some of the distinctive properties of the sulfur-containing amino acids. Methionine is the initiating amino acid in the synthesis of virtually all eukaryotic proteins; N-formylmethionine serves the same function in prokaryotes. Within proteins, many of the methionine residues are buried in the hydrophobic core, but some, which are exposed, are susceptible to oxidative damage. Cysteine, by virtue of its ability to form disulfide bonds, plays a crucial role in protein structure and in protein-folding pathways. Methionine metabolism begins with its activation to S-adenosylmethionine. This is a cofactor of extraordinary versatility, playing roles in methyl group transfer, 5'-deoxyadenosyl group transfer, polyamine synthesis, ethylene synthesis in plants, and many others. In animals, the great bulk of S-adenosylmethionine is used in methylation reactions. S-Adenosylhomocysteine, which is a product of these methyltransferases, gives rise to homocysteine. Homocysteine may be remethylated to methionine or converted to cysteine by the transsulfuration pathway. Methionine may also be metabolized by a transamination pathway. This pathway, which is significant only at high methionine concentrations, produces a number of toxic endproducts. Cysteine may be converted to such important products as glutathione and taurine. Taurine is present in many tissues at higher concentrations than any of the other amino acids. It is an essential nutrient for cats.

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The Sulfur-Containing Amino Acids: An Overview

Thousands of pet cats die each year with dilated cardiomyopathy, the cause of which is unknown. Although taurine is present in millimolar concentrations in the myocardium of all mammals, taurine depletion has not previously been associated with a decrease in myocardial function in any species. In this study, low plasma taurine concentrations associated with echocardiographic evidence of myocardial failure were observed in 21 cats fed commercial cat foods and in 2 of 11 cats fed a purified diet containing marginally low concentrations of taurine for 4 years. Oral supplementation of taurine resulted in increased plasma taurine concentrations and was associated with normalization of left ventricular function in both groups of cats. Since myocardial concentrations of taurine are directly related to plasma concentrations and low plasma concentrations were found to be associated with myocardial failure in cats, a direct link between decreased taurine concentration in the myocardium and decreased myocardial mechanical function is proposed.

https://science.sciencemag.org/content/sci/237/4816/764.full.pdf

Myocardial failure in cats associated with low plasma taurine: a reversible cardiomyopathy

From the foregoing discussion of the nutritional requirements and some of the metabolic anomalies of the cat, it is clear that the cat is adapted to eating a carnivorous diet. It may, however, have less capability than omnivores and herbivores to adapt to wide ranges in dietary composition. For example, the lack of ability to synthesize sufficient vitamin A from carotene, ornithine from glutamic acid, arachidonate from linoleate, and taurine from cysteine results from a complete deletion or severe limitation of the enzyme or pathway that makes each nutrient. Other nutrient requirements, such as the absolute requirement for niacin and the high protein requirement, appear to result from the high activity of one or more enzymes and the fact that these enzymes are not adaptive in the cat. For example, the cat cannot decrease picolinic carboxylase in order to force tryptophan toward the niacin-synthetic pathway (244) nor can it decrease the urea cycle enzymes when dietary protein is decreased in the diet in order to conserve nitrogen (209). Indeed, the cat appears to have less capability to adapt to most changes in dietary composition because it cannot change the quantities of enzymes involved in the metabolic pathways (209). This evolutionary development has resulted in more stringent nutritional requirements for cats than for omnivores such as the rat, dog, and man. What little evidence exists for other carnivore species leads us to suggest that this pattern may well be common among other strict carnivores. The metabolic differences between the cat and omnivores provide the researcher with a useful animal model for studying the biochemical basis of some nutrient requirements. For example, because there is no significant conversion of linoleate to arachidonate in cat liver (101, 150, 231), the physiological functions of linoleate can be determined independent of it having a role as a precursor of arachidonate (150). This has not been possible with other species. It is anticipated that further studies of the nutrition of the cat will increase our understanding of metabolic adaptation and nutrient functions.

Nutrition of the domestic cat, a mammalian carnivore.

Rumen microbial growth rates and yields: effect of amino acids and protein.

The concentrations of iron, copper, zinc, manganese, calcium and magnesium, as well as protein, carbohydrate and fat, were analyzed in rat milk during the course of lactation in rats fed a purified diet. As serial milking has been demonstrated to affect milk composition (1), lactating rats were milked only once at various times from days 0 to 28 after parturition. Concentration of iron decreased rapidly from 9 to 5 micrograms/ml during the 1st week of lactation and changed little thereafter. Similarly, copper concentration decreased considerably in early lactation, from 9 to 2 micrograms/ml, but then remained constant. Zinc concentration did not decrease during the 1st week of lactation, but dropped from 14 micrograms/ml in the 2nd week of lactation to 8-10 micrograms/ml in mature milk. Manganese was unique as its concentration decreased during the early days of lactation, from 0.3 to 0.1 microgram/ml, with a subsequent rise in late lactation back to 0.3 microgram/ml. Calcium and magnesium concentrations increased somewhat in early lactation and decreased slightly in later lactation, but the changes were fairly small as compared to the trace elements. Developmental patterns for protein, carbohydrate and fat were not very pronounced, although protein and carbohydrate increased somewhat in early lactation and later decreased. These data demonstrate that the nutrient intake of the suckling changes markedly during the early neonatal period. These changes should be taken into account in evaluating data on the trace element composition of tissues of suckling rats.

Developmental changes in composition of cats milk: trace elements, minerals, protein, carbohydrate and fat.

The activities of three urea cycle enzymes, several nitrogen catabolic, gluconeogenic, and lipogenic enzymes were measured in the liver of adult cats fed: a commercial kibble; a 17.5 or 70% protein purified diet, or starved for 5 days. Except for an increase in tyrosine transaminase (EC 2.6.1.5) after feeding the high protein diet, there were no changes in the activities of the hepatic enzymes as influenced by dietary protein level. Likewise, starvation had a minimal effect on the activities of these enzymes as compared to that found in similar experiments in rats. These results indicate that the cat may have only minimal capabilities for enzyme adaptation as compared to that found in many herbivores and omnivores and may provide an explanation as to why cats have an unusually high protein requirement as compared to many other mammals.

James G. Morris

Papers

Myocardial failure in cats associated with low plasma taurine: a reversible cardiomyopathy

Nutrition of the domestic cat, a mammalian carnivore.

Rumen microbial growth rates and yields: effect of amino acids and protein.

Developmental changes in composition of cats milk: trace elements, minerals, protein, carbohydrate and fat.

Lack of hepatic enzymatic adaptation to low and high levels of dietary protein in the adult cat.