Yeast protein identity

In terms of amino acids bacterial protein is similar to fish protein. The yeast s protein is almost identical to soya protein fungal protein is lower than yeast protein. In addition, SCP is deficient in amino acids with a sulphur bridge, such as cystine, cysteine and methionine. SCP as a food may require supplements of cysteine and methionine whereas they have high levels of lysine vitamins and other amino acids. The vitamins of microorganisms are primarily of the B type. Vitamin B12 occurs mostly hi bacteria, whereas algae are usually rich in vitamin A. The most common vitamins in SCP are thiamine, riboflavin, niacin, pyridoxine, pantothenic acid, choline, folic acid, inositol, biotin, B12 and P-aminobenzoic acid. Table 14.4 shows the essential amino acid analysis of SCP compared with several sources of protein. 

Miniaturization of HPLC-ICP-MS is an important issue in bioanalytical chemistry when small amounts of sample (e.g., single cells) need to be investigated.33 ICP-MS (with an octopole collision cell) in combination with nano-HPLC (75 pun column) was optimized for the detection of selenopeptides in a selenium-yeast protein digest after 100-fold preconcentration on a C18 capillary precolumn (300 (im column for salt removal and cleanup).34 Under identical separation and preconcentration conditions, electrospray MS/MS (using Nanospray qQqToF-MS - QSTAR from Applied... 

Isolation of Proteins with a Reduced Nucleic Acid Level. The procedure is virtually identical to that described for succinylation of yeast proteins (87). In a typical experiment proteins, together with NA, were extracted from the disrupted yeast cells at pH 8.5-9.0 and centrifuged at 15,000 rpm for 30 min at 5°C. Citraconic anhydride then was added in small increments to the supernatant with constant stirring while the pH was maintained between 8.0-8.5 by adding 3.5IV NaOH. After the stabilization of the pH, the pH of the solution was decreased to 4.2 to precipitate the proteins. Protein then was separated by centrifugation, dissolved in water (pH adjusted 8.5), dialyzed extensively against water (pH 8.5) at 5°C, and lyophilized. 

Eons apart. The amino acid sequences of a yeast protein and a human protein carrying out the same function are found to be 60% identical. However, the corresponding DNA sequences are only 45% identical. Account for this differing degree of identity. 

FIGURE 10.18 A model for the structure of the a-factor transport protein in the yeast plasma membrane. Gene duplication has yielded a protein with two identical halves, each half containing six transmembrane helical segments and an ATP-binding site. Like the yeast a-factor transporter, the multidrug transporter is postulated to have 12 transmembrane helices and 2 ATP-binding sites. 

A representative set of a- and -keto esters was also tested as substrates (total 11) for each purified fusion protein (Figure 8.13b,c) [9bj. The stereoselectivities of -keto ester reductions depended both on the identity of the enzyme and the substrate stmcture, and some reductases yielded both l- and o-alcohols with high stereoselectivities. While a-keto esters were generally reduced with lower enantioselec-tivities, it was possible to identify pairs of yeast reductases that delivered both alcohol antipodes in optically pure form. These results demonstrate the power of genomic fusion protein libraries to identify appropriate biocatalysts rapidly and expedite process development. 

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. 

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