Yeasts amino acid composition

The data presented in Table 3, which includes the amino acid composition of baker s yeast and Candida krusei cytochrome c for comparison, show that Ustilago and Neurospora cytochrome c contain the same number of total residues. In seven instances, the number of residues of a particular amino acid/mole are identical. Thus, even in the absence of a sequence for the Ustilago cytochrome it can be concluded that this protein, unlike the siderochromes, has suffered little alteration in the progression from the Ascomycetes to the Basidiomycetes. This can be ascribed to the varying function of the two types of molecules. Cytochrome c must fit into a relatively specific slot bounded by a reductase and an oxidase and it has hence evolved much more slowly than the more freely acting transport agents where the specificity constraints are less demanding. 

A comparison of the mean amino acid composition of the soils with those of algae, bacteria, fungi, and yeasts showed the greatest similarity to that of bacteria. [4] This suggests, perhaps not too surprisingly, a major role for microorganisms in the synthesis in the soil of amino acids, peptides and proteins from plant and animal residues, and also explains the relatively uniform amino acid composition in different soils. 

Table IV. Amino acid compositions of the APPL associated proteins, of yeast extract and of the cellular soluble proteins obtained from...

Found in the chromatin of all eukaryotic cells, histones have molecular weights between 11,000 and 21,000 and are very rich in the basic amino acids arginine and lysine (together these make up about one-fourth of the amino acid residues). All eukaryotic cells have five major classes of histones, differing in molecular weight and amino acid composition (Table 24-3). The H3 histones are nearly identical in amino acid sequence in all eukaryotes, as are the H4 histones, suggesting strict conservation of their functions. For example, only 2 of 102 amino acid residues differ between the H4 histone molecules of peas and cows, and only 8 differ between the H4 histones of humans and yeast. Histones HI, H2A, and H2B show less sequence similarity among eukaryotic species. 

Table II. Amino Acid Composition of Yeast Protein Isolated by Different Methods (Expressed as g/l6 g Nitrogen)...

All amino acids, except proline, may be used by Saccharomyces cerevisiae in grape juice fermentation. Amino acids can be directly used to synthesize proteins. However, the amino acid composition of the grape juice is not necessarily similar to the needs of the cell. For that reason, yeasts must use the remaining amino acids to synthesize those which it lacks (Hensche and Jiranek 1993 Ribereau-Gayon et al. 2000b). In this case, ammonia is incorporated into other amino acids whereas the carbon skeleton is metabolized by the cell. 

Moreno-Arribas, V., Pueyo, E., Polo, M.C. and Martin-Alvarez, PJ. (1998b). Changes in the amino acid composition of the diffeent nitrogenous fractions during the aging of wine with yeast. J. Agric. Food Chem., 70, 309-317. 

Thioredoxin from yeast has been obtained in two forms (I and II) of which thioredoxin II has been purified to homogeneity (43). Both yeast thioredoxins are able to serve as hydrogen donors for the ribonucleotide reductase from E. coli. The molecular weight (12,600) of thioredoxin II is similar to that of thioredoxin from E. coli. Although both yeast thioredoxins contain only one tryptophan residue and although their amino acid compositions differ markedly from that of E. coli thioredoxin, the amino acid sequences around the disulfide bridge of these three thioredoxins are identical ... 

A thioredoxin has also been partially purified from L. leichtnannii (39). Although this thioredoxin is similar in size (MW approximately 12,000) to the E. coli thioredoxin, it is not able to function as a substrate for the E. coli thioredoxin reductase. More recently thioredoxins have been purified to homogeneity from rat Novikoff ascites hepatoma (127) and from calf liver (45). The properties of these two thioredoxins are quite similar (MW 11,400 and 12,000 respectively). The amino acid compositions however, are different. For instance the Novikoff tumor thioredoxin contains six half-cysteine residues, whereas calf liver thioredoxin has only four. Both these thioredoxins have a tendency to aggregate in the oxidized form. This aggregation is probably due to mixed sulfide formation between the additional sulfhydryl groups. Like yeast thioredoxin II, calf liver thioredoxin contains only one tryptophan residue unfortunately the tryptophan content of Novikoff tumor thioredoxin was not determined. 

Thioredoxin reductases have also been purified from yeast (43, 134) and from rat fiver (135). Thioredoxin reductase from yeast is a flavo-protein with a molecular weight of approximately 75,000 and consists of two subunits, each containing one molecule of FAD. Although the amino acid composition of this thioredoxin reductase is quite different from that of E. coli, both enzymes contain 5 half-cystine residues and have almost identical absorption spectra. Like the E. coli enzyme, thioredoxin reductase from yeast is completely inhibited by p-chloro-mercuriphenylsulfonate (PCMS) only in the presence of NADPH suggesting that the yeast enzyme also contains a disulfide bridge at the catalytic site. 

While the bias in the amino acid composition of yeast PrD sequences is now well established, the importance of the primary amino acid sequence for prion formation has been the subject of some debate. Several yeast PrDs (Sup35, Rnql, Newl) contain oligopeptide repeats that are important for efficient propagation of the prion form of that protein [108, 116, 117]. This is especially so for the yeast [PS/+] prion which possesses five imperfect nonapeptide repeats with a consensus sequence PQGGYQQYN (Fig. 6). This sequence bears a striking resemblance to the five octarepeats found in mammalian PrP and which have the consensus sequence PHGGGWGQ. 

Organisms like the ciliated protozoan Paramecium, baker s yeast Saccharo-myces cerevisiae and the Gram-negative bacterium Escherichia coli have non-selective, mechanically gated cation-channels. The channel from yeast has conductance comparable to nAChR (186). The voltage sensitive sodium channels from eel electroplax have an amino acid composition remarkably similar to that of nAChR and the repeats from Drosophila sequences are closely comparable to the ones from eel and rat (187). 

FAO food protein standard. All essential amino acids are present in amounts above or close to the required levels, with the exception of the sulfur-containing amino acids (methionine and cystein), which was expected, as yeast protein are described to have a low content of these amino acids [8, 23, 38]. Nevertheless, methionine and/or cysteine levels are above that described in literature for other yeast [7, 8, 23, 34, 40]. Among the nonessential amino acids, glutamic and aspartic acid are present in higher amounts as previously found for other yeasts [7, 23, 38]. Considering the overall amino acid composition, there seems to be interesting prospects for D. hansenii biomass use as a food/feed supplement. 

The amino acid composition of the must also affects the formation of H2S by yeast. Besides cysteine and homocysteine, the following amino acids promote the production of H2S aspartic and glutamic acids, glycine, histidine, homoserine, lysine, ornithine, threonine and serine. Methionine prevents the formation of H2S by retroinhibiting the activation channel and reducing sulfates. 

In recent years several attempts have been made to isolate some of the translocator proteins. Major progress has been achieved with the purification of the adenine nucleotide translocator. This protein has been isolated in its native form and its molecular weight and immunological properties have been characterised [57,104]. The carrier protein from beef heart and rat liver is a dimer. The of each of the subunits is 30000. In heart, the carrier protein makes up 10% of the total mitochondrial protein. The amino acid composition of the yeast protein has been determined recently [105]. 

Petite mutants spontaneous mutants, chiefly yeasts, with chemical or physical defects in the respiratory chain. P. m. grow very slowly and form small ( petite ) colonies on nutrient agar. The same phenotype can be produced by a chromosomal mutation (segregational petite), or a mutation in the mitochondrial DNA (vegetative or neutral petite). In the latter case, mitochondrial structure is considerably altered, largely due to changes in the amino acid composition of the structural proteins of the inner mitochondrial membrane. Since these structural proteins are important for the correct arrangement and conformation of the respiratory chain enzymes, the effect of petite mutation on the respiratory chain is probably secondary. 

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