Enzymes residual protein

Protein (Section 26.4) A large peptide containing 50 or more amino acid residues. Proteins serve both as structural materials and as enzymes that control an organism s chemistry. 

In mammalian cells, the two most common forms of covalent modification are partial proteolysis and ph osphorylation. Because cells lack the ability to reunite the two portions of a protein produced by hydrolysis of a peptide bond, proteolysis constitutes an irreversible modification. By contrast, phosphorylation is a reversible modification process. The phosphorylation of proteins on seryl, threonyl, or tyrosyl residues, catalyzed by protein kinases, is thermodynamically spontaneous. Equally spontaneous is the hydrolytic removal of these phosphoryl groups by enzymes called protein phosphatases. 

Phosphorylation by protein kinases of specific seryl, threonyl, or tyrosyl residues—and subsequent dephosphorylation by protein phosphatases—regulates the activity of many human enzymes. The protein kinases and phosphatases that participate in regulatory cascades which respond to hormonal or second messenger signals constimte a bio-organic computer that can process and integrate complex environmental information to produce an appropriate and comprehensive cellular response. 

Solubilization of an active H,K-ATPase is also a prerequisite for reconstitution of the enzyme into liposomes. With these H,K-ATPase proteoliposomes it is then possible to study the transport characteristics of pure H,K-ATPase, without the interference of residual protein contamination that is usually present in native vesicular H,K-ATPase preparations. Rabon et al. [118] first reported the reconstitution of choleate or n-octylglucoside solubilized H,K-ATPase into phosphatidylcholine-cholesterol liposomes. The enzyme was reconstituted asymmetrically into the proteoliposomes with 70% of the pump molecules having the cytoplasmic side extravesicular. In the presence of intravesicular K, the proteoliposomes exhibited an Mg-ATP-dependent H transport, as monitored by acridine orange fluorescence quenching. Moreover, as seen with native H,K-ATPase vesicles, reconstituted H,K-... 

The carboxy terminus of the ft receptor was essential for agonist-induced desensitization [83, 132] since truncation of the receptor prevented desensitization. Like those findings with the k receptor, the enzyme G protein receptor kinase (GRK) appears to be involved in the desensitization process, since blockade of GRK prevented the desensitization process. Wang [132] has proposed that GRK catalyzes the phosphorylation of a series of serine/threonine residues in the C-terminus of the fi receptor to desensitize the receptor. 

Based on these results, several different commercial and experimental protease samples were obtained from enzyme companies and were tested for starch yield using the enzymatic corn wet milling process (Figure 3). Two commercial protease enzymes (enzymes A and C) gave starch yields comparable to the conventionally wet milled sample. Pasting properties, residual protein in starch, and surface characteristics of starch samples obtained from... 

This zinc-dependent enzyme [EC 3.4.15.1] (also known as dipeptidyl carboxypeptidase I, dipeptidyl-dipeptidase A, kininase II, peptidase P, and carboxycathepsin) catalyzes the release of a C-terminal dipeptide at a neutral pH. The enzyme will also act on bradykinin. The presence of prolyl residues in angiotensin I and in bradykinin results in only single dipeptides being released due to the activity of this enzyme, a protein which belongs to the peptidase M2 family. The enzyme is a glycoprotein, generally membrane-bound, that is chloride ion-dependent. 

Many enzymes (and protein substrates) require free thiol residues for proper conformation and/or activity. In this case, including a thiol reagent (such as 2-mercaptoetha-nol, dithiothreitol, dithioerythritol, or cysteine) may maintain activity. 

Ribonuclease A (RNase A) was selected as the target enzyme for solid-phase synthesis because its sequence was known (Scheme S), 22 25 and an X-ray structure had been deduced. 24 Importantly, it had been shown that this 124-residue protein could be reduced and unfolded and then reoxidized to re-form the four disulfide bonds with recovery of full enzymatic activity. 25 ... 

I was thinking particularly of electrostatic interactions between enzyme residues and substrate molecules. Let us compare the hydrophilic cytoplasmic phase (say, with dielectric constant e = 80) and the hydrophobic regions within membranes (say, with e = 2). Is it possible that protein-substrate interactions may be enhanced in certain membrane-associated enzyme schemes That is, might specific intermolecular forces play a more significant role in influencing the site-to-site migration of intermediate substrates, as compared to the same system in the hydrophilic phase [R. Coleman, Biochim. Biophys. Acta, 300, 1 (1973) P. A. Srere and K. Mosbach, Anti. Rev. Microbiol., 28, 61 (1974) and H. Frohlich, Proc. Nat. Acad. Sci. (U.S.), 72, 4211 (1975).]... 

A single P strand can also be wound into a cylinder with the hydrogen bonds running parallel to the helix axis. A right-handed parallel P helix of this type has been found in the bacterial enzyme pectate lyase.121122 The polypeptide chains of the 353-residue protein contain seven complete turns of about 22... 

In one of the haloacid dehalogenases, a 232-residue protein for which the three-dimensional structure is known,8 9 Asp 10 is in a position to carry out the initial attack which would give an enzyme-bound intermediate with an ester linkage ... 

Its role is to cut a hole in the bacterial cell wall to permit injection of the virus own DNA. Egg white lysozyme, the first enzyme for which a complete three-dimensional structure was determined by X-ray diffraction,55 is a 129-residue protein. 

Several selenoproteins have been found in certain bacteria and archaea. A hydrogenase from Methano-coccus vannielii contains selenocysteine.559 560 This enzyme transfers electrons from H2 to the C-5 si face of the 8-hydroxy-5-deazaflavin cofactor F q (Section B,4). The same bacterium synthesizes two formate dehydrogenases (see Fig 15-23), one of which contains Se. Two Se-containing formate dehydrogenases are made by E. coli. One of them, which is coupled to a hydrogenase in the formate hydrogen-lyase system (see Eq. 15-37), is a 715-residue protein containing selenocysteine at position 140.561-563 The second has selenocysteine at position 196 and functions with a nitrate reductase in anaerobic nitrate respiration.561... 

A single mutation (Pro 101 —> Ser) in the 427-residue protein from E. coli makes the enzyme more resistant to the herbicide.28 Other mutations affect binding and catalysis.29... 

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