Carboxyl terminus, protein

The digestion of the protein, after heme removal, using Glu-C endoproteinase was also carried out. This enzyme cleaves the polypeptide backbone on the carboxyl terminus of a glutamic acid residue and in this case yielded twelve chromatographic responses. Despite two of these arising from unresolved components, molecular weight information was obtained from 15 polypeptides, one of which was the intact protein, covering the complete sequence, as shown in Table 5.10. 

The KKXX sequence is present at the carboxyl terminus of ER membrane proteins, while the H/KDEL is present in soluble ER proteins, such as the aforementioned... 

The inositol polyphosphate 5-phosphatases belong to a family of enzymes that terminate the signals generated by inositol lipid kinases and PLC. To date, two major types of 5-phosphatase have been identified, both of which share a common 5-phosphatase domain of approximately 300 amino acids, with several highly conserved motifs. Type-I enzymes are 43-65 kDa and preferentially hydrolyze 1(1,4,5)P3 and 1(1,3,4,5)P4, with the attendant formation of I(1,4)P2 and 1(1,3,4)P3, but have little or no activity towards membrane-bound phosphoinositides. The pro-totypic form of a type-15-phosphatase is a 43 kDa protein that is post-translationally modified by farnesylation of the carboxyl terminus CAAX motif this modification juxtaposes the enzyme with the membrane. Type-II enzymes are larger (75-160 kDa) and will hydrolyze both water-soluble inositol phosphates and lipids that... 

As mentioned earlier, by far the largest number of zinc enzymes are involved in hydrolytic reactions, frequently associated with peptide bond cleavage. Carboxypeptidases and ther-molysins are, respectively, exopeptidases, which remove amino acids from the carboxyl terminus of proteins, and endopeptidases, which cleave peptide bonds in the interior of a polypeptide chain. However, they both have almost identical active sites (Figure 12.4) with two His and one Glu ligands to the Zn2+. It appears that the Glu residue can be bound in a mono- or bi-dentate manner. The two classes of enzymes are expected to follow similar reaction mechanisms. 

Bacterial hosts are inappropriate choices for expression of proteins such as the blue copper proteins stellacyanin, laccase, and ceruloplasmin which are extensively glycosylated. In these cases, it may be necessary to employ tissue cultures of appropriate origin to obtain the native protein. In this regard, the amino-terminal half of human serum transferrin, which lacks carbohydrate, has been expressed in high yield in baby hamster kidney cells by Funk et al. [13], while the glycosylated carboxyl-terminus has proved to be more problematic [103]. 

The ribosome translates the message in the 5 to 3 direction, synthesizing the protein from amino terminus to carboxyl terminus. 

During translation, the amino adds are attached to the 3 ends of their respective tRNAs. The aminoacyl-tRNAs are situated in the P and A sites of the ribosome as shown in Figure 1-4-8, Sotice that the peptide bond forms between the carboxyl group of the amino add (or growing peptide) in the P site and the amino group of the ne rt amino add in the A site. Proteins are syn-desized from the amino to the carboxyl terminus. 

Elongation is a three-step cycle that is repeated for each amino add added to the protein after the initiator methionine. Each cycle uses four high-energy bonds (two from the ATP used in amino add activation to charge the tRNA, and two from GTP). During elor tion, the ribosome moves in the 5 to 3 direction along the mRNA, synthesizing the protein from amino to carboxyl terminus. The three steps are ... 

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