Phosphorylation activation

Figure 19-5. Variation in glucose phosphorylating activity of hexokinase and glucokinase with increase of blood glucose concentration. The for glucose of hexokinase is 0.05 mmol/L and of glucokinase is 10 mmol/L.

Fig. 4. Domain complementation schemes. (A) A domain complementation. The H554A site-directed mutant is inactive in P-enolpyruvate-dependent mannitol phosphorylation because it cannot accept a phosphoryl group from P-FIpr. The measure of A domain activity is its ability to restore mannitol phosphorylation activity to this mutant. A domain activity in the AB subcloned protein can also be measured. (B) B domain complementation. The C384S site-directed mutant is inactive in P-enolpyruvate-dependent mannitol phosphorylation because it cannot pass the phosphoryl group from H554 on its own A domain to mannitol. The measure of B domain activity is its ability to restore mannitol phosphorylation activity to this mutant. B domain activity in the AB subcloned protein can also be measured. (C) C domain complementation. The activity of the C domain is measured by complementation with the purified AB domain.

The function of the B domain has been confirmed by subcloning and preliminary kinetic measurements. We subcloned the AB domain of E. coli II, residues 348-637, after inserting a restriction site at a position corresponding to residue 348. The purified protein restored mannitol phosphorylation activity when measured with the A domain assay in Fig. 4A, and the B domain assay in Fig. 4B [42]. The B domain... 

Chemical modifications like alkylation with (A-ethylmaleimide (NEM) or oxidation with diamide that inhibit the phosphorylation activity of the enzyme did not seem to have any significant effect on the high affinity binding site when the enzyme was solubilized in the detergent decyl-PEG [69,41]. However, in the intact membrane these treatments reduced the affinity by a factor of 2-3. The reduction of the affinity was exclusively due to modification of the cysteine residue at position 384 in the B domain [69]. Apparently, the detergent effects the interaction between the B and C domains. 

S. typhimurium normally transport trehalose via the galactose permease and are able to grow on this substrate in the complete absence of PTS phosphorylating activity. However, in S. typhimurium which lack a functional galactose permease, IfMan appears to be able to transport trehalose [78]. There is no evidence that trehalose is phosphorylated in this process, again pointing to Il "-dependent transport in the facilitated diffusion mode. 

In spite of having no intrinsic catalytic domains, activation of T lymphocytes commences with tyrosine phosphorylations, activation of PLC-v with production of IP3 and DAG, and elevation of cytosolic free Ca2+. Thus, the consequences of receptor ligation are not dissimilar from those induced by the receptors for EGF or PDGF. An early study trying to explain the induction of tyrosine kinase activity resulted in the discovery of the nonreceptor protein tyrosine kinase Lck (p56lck), a T-cell-specific member of the Src family. Lck is associated with the cytosolic tail of CD4 (in helper T cells) or CD8 (in cytotoxic T cells) (Figure 8.14). As mentioned, the extracellular domains of these... 

When administered as valaciclovir, aciclovir is released during absorption, and 60% of the drug reaches the bloodstream, as described above. Site activation also occurs in herpesvirus-infected cells where aciclovir is biochemically transformed to the phosphorylated active drug by virus-specific thymidine kinase [74]. 

Toxoflavin reduced the respiratory oxygen consumption of mitochondria and suppressed the oxidative phosphorylation activity (91 Mil). 

The critical feature of CREB protein activation is phosphorylation, which is required for CREB-mediated stimulation of transcription [16]. PKA phosphorylates CREB on a serine positioned at amino acid 133 in the CREB protein sequence. How phosphorylation activates... 

While several studies reported that PLB was present in smooth muscle, very little was known about its role in Ca2+ handling. Some evidence suggested that in addition to A-kinase pathway phosphorylation, activation of the G -kinase pathway was associated with PLB phosphorylation. The latter was of particular interest to vascular smooth muscle, for which endothelium-dependent relaxation via nitric oxide (NO) made the mechanism of G-kinase-mediated relaxation of considerable physiological significance (Karczewski et al 1998). 

P was incorporated into specific serine residues on the phosphorylase. Similar phosphorylation activated the liver enzyme (Sutherland et al., 1956). 

Enzyme Activity when phosphorylated Activity when dephosphorylated Allosteric activators Allosteric inhibitors... 

Phosphate is charged (2—) so when it is incorporated into an enzyme, alterations in the electrostatic attractions between parts of the enzyme molecule will occur causing a change in the three-dimensional conformation of the protein. The effect may be to expose the active site to allow substrate binding (if phosphorylation activates the enzyme) or may hide the active site, so switching off the enzyme. 

The mechanism by which A-esterases hydrolyze organophosphates is not completely understood. Involvement of a phosphorylated active-site cysteine and displacement of an activated H20 molecule are two possible hypotheses (see Sect. 3.7.1) [56], A-Esterases comprise enzymes that hydrolyze aryl esters, paraoxon (2.2) and related organophosphate pesticides, and diisopropyl-fluorophosphate (DFP, diisopropyl phosphorofluoridate, 2.3) and related compounds, including nerve gases. These enzymes are found in the current nomenclature listed under arylesterases, aryldialkylphosphatase, and diisop-ropyl-fluorophosphatase. 

Since the enzyme that is most specific in the ubiquitin-conjugation reaction, E3, is also highly regulated, temporal regulation of ubiquitination is easily achieved. For example, if a given E3 is activated by a protein kinase, activation of the E3 is tied to the stimulation of the kinase. For example, phosphorylation activates the ARC ubiquitin ligase. An interesting example is that of serum-inducible kinase (SNK). SNK stimulates... 

Premont, R. T., Inglese, J., and Lefkowitz, R. J. (1995) Protein kinases that phosphorylate activated G protein-coupled receptors. EASES J. 9, 175-82. 

Fig. 5.8. Desensitization of G-protein-coupled receptors via cAMP-dependent protein kinases. Starting from an activated receptor R, the signal is transmitted via the G<,-subunit of the G-protein to adenylyl cyclase. The latter is activated and forms cAMP. This activates a protein kinase of type A that passes the signal in the form of a Ser/Thr-specific protein phosphorylation to substrate proteins. One of the substrates is also the receptor that is phosphorylated in the region of the cytoplasmic domain by the activated protein kinase A. The ligand-bound receptor is preferentially phosphorylated. As a consequence of phosphorylation, activation of further G-proteins by the receptor is suppressed.

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