Introduction to Cell Biology
Anthony R. Mundy, John M. Fitzpatrick, David E. Neal, Nicholas J. R. George in The Scientific Basis of Urology, 2010
Specific amino acid residues within a protein act as acceptors of phosphate groups. Phosphorylation occurs at tyrosine, serine, or threonine residues, and the kinases that catalyze this transfer are highly specific. Kinases can have a transmembrane localization [e.g., receptor tyrosine kinases, which include the epidermal growth factor receptor (EGFR) family] or can be found intracellularly [Src family kinases, mitogen-activated protein (MAP) kinases, Akt]. The target proteins of kinases include both catalytic proteins such as other kinases, or noncatalytic proteins such as adapters or scaffolding proteins that form the skeleton of multiprotein signaling complexes. Another class of enzymes known as phosphatases can remove the phosphate group from a particular residue of a protein, thereby altering its activity. The antagonistic action of kinases and phosphatases thus tightly regulates both the duration and magnitude of signal transduction by phosphorylation (Fig. 4A).
Fate of Radiometabolites
Lelio G. Colombetti in Principles of Radiopharmacology, 1979
The enzymes involved in tracers metabolism affect the fate of these tracers by modification of their polarity, solubility, and even their molecular size. The best known are enzymes of deiodination of iodinated organic tracers, enzymes of oxidation, hydroxylation, oxidative deamination, dealkylation, and oxidative scission of moieties. N methyl and O methyl transferases transfer methyl groups from a tracer to a biological acceptor. N demethylation occurs very frequently. Cytochrome P 450 is involved in the phenyl hydroxylation system. Several compounds may induce enzymatic activity, increasing the metabolism of tracers. Among them, phenobarbital and chlorinated insecticides seem to be the most active. The enzymatic induction is correlated with the proliferation of the smooth endoplasmic reticulum in the liver cells, which is accompanied by an increase in liver weight of 20 to 50%. Ester hydrolysis, reduction, and conjugation are catalyzed by esterases, reductases, and conjugases. The activity of these enzymes proceeds to the modification of hydrophobic groups such as aromatic rings, methyl and ethyl radicals, chlorinated or iodinated moieties, to hydrophilic groups, namely: hydroxyls, carboxyls, sulfonates, sulfonamides, amines, etc. Phosphatases induce the transfer of a phosphate group or of a phosphoryl group from organic phosphates and long chain phosphates.
Nuclear Protein Kinases
Lubomir S. Hnilica in Chromosomal Nonhistone Proteins, 2018
The relative importance of the various types of phosphatases in dephosphorylating nuclear proteins is yet to be elucidated, primarily because only a few nuclear phosphatases have been purified and characterized. The acid and alkaline phosphatases exhibit relatively low efficiency with nuclear proteins as substrates, and are more likely involved in the metabolism of low molecular weight phosphate esters. A histone phosphatase has been extensively purified from liver nuclei which dephosphorylates histones and protamines, but not nonhistones or low molecular weight phosphate esters.456,461–463 This protein phosphatase has a subunit molecular weight of 34,000 and exhibits optimal enzymatic activity at a pH of about 7. It appears in multiple forms which are believed to be due to association of the same catalytic subunit with different association of the same catalytic subunit with different proteins or regulatory factors. The enzyme does not require divalent cations or cyclic nucleotides, but is 90% inhibited by 1 mM Zn ++. This inhibition by zinc ions is in marked contrast to the behavior of alkaline phosphatase, which is a zinc-requiring metalloenzyme. The purified histone phosphatase is similar in many ways to a cytoplasmic protein phosphatase which dephosphorylates phosphorylase, protein kinase, and other cytoplasmic phosphoproteins.
An update of targeted therapeutic options for primary Sjögren syndrome: current status and future development
Published in Expert Opinion on Pharmacotherapy, 2021
Soledad Retamozo, Antoni Sisó-Almirall, Alejandra Flores-Chávez, Manuel Ramos-Casals, Pilar Brito-Zerón
Kinases are a group of enzymes that transfer a phosphate group to a protein, playing a key role in maintaining cellular function by turning protein function on, while other enzymes (phosphatases) reverse this action [77]. Approximately 538 known kinases are encoded in the human genome, which are subdivided into seven families of typical and seven families of atypical protein kinases. One of the more recent therapeutic approaches to control autoimmune and inflammatory responses has been to target the activity of kinases [78]. Inhibition of kinases may be achieved by means of small molecules designed to interfere with the enzyme regardless of its cellular location, or by monoclonal antibodies (mAbs) targeting kinase receptors located at the cell surface. Small-molecule inhibitors are molecules ≤500 Da in size (the names of the molecules use the stem ‘-ib’ at the end) [79], while the names of mAbs use the general stem ‘-mab,’ with specific sub-stems according to the source (‘-ximab’ for chimeric mAbs, ‘zumab’ for humanized mAbs, and ‘-mumab’ for fully human mAbs) [80].
Network pharmacology and experimental investigation of Rhizoma polygonati extract targeted kinase with herbzyme activity for potent drug delivery
Published in Drug Delivery, 2021
Yingqiu Xie, Chengling Mu, Bexultan Kazybay, Qinglei Sun, Aidana Kutzhanova, Guldan Nazarbek, Na Xu, Lazzat Nurtay, Qian Wang, Amr Amin, Xugang Li
It is well-documented that kinases play essential roles in the regulation of metabolic processes of cells and are further involved in critical differentiation, proliferation, apoptosis, and cell development (Fabbro et al., 2015). Studies also show that phosphatases are involved in these phosphorylation–dephosphorylation processes along with kinases. It has been recognized that phosphatase might be essential in targeting cancer cell growth by disrupting kinase signaling pathways (Heinrich et al., 2018). Therefore, we hypothesize that nanozymatic phosphatase activity of RP might inhibit or disrupt the kinase signaling pathways, hence blocking cellular proliferation including cancer cells. It is additionally expected that RP ingredients could have a larger effect in combination with precision kinase inhibitor drugs against cancer cell growth. We further examined whether RP ingredients could have the potential to be used to inhibit cell growth in combination with kinase inhibitors which might be applied in treatments against other types of diseases in the future as well because many diseases are induced or related to kinase signaling for their progression.
Effects of quercetin on the pharmacokinetics of losartan and its metabolite EXP3174 in rats
Published in Xenobiotica, 2019
Qingling Zhao, Jinlan Wei, Hongying Zhang
The Caco-2 cell line was obtained from the American Type Culture Collection (Manassas, VA). The Caco-2 cells were cultured in DMEM high glucose medium containing 15% FBS, 1% NEAA and 100 U/mL penicillin and streptomycin. The cells were cultured at 37 °C with 5% CO2. For transport studies, the cells at passage 40 were seeded on transwell polycarbonate insert filters (1.12 cm2 surface, 0.4 μm pore size, 12 mm diameter; Corning Costar Corporation, Cambridge, MA) in 12-well plates at a density of 1 × 105 cells/cm2. Cells were allowed to grow for 21 days. For the first seven days, the medium was replaced every two days, and daily thereafter. The transepithelial electrical resistance (TEER) of the monolayer cells was measured using Millicell ERS-2 (Millipore Corporation, Billerica, MA), and TEER exceeding 400 Ω·cm2 was used for the flux experiment. The integrity of the Caco-2 monolayers was confirmed by the paracellular flux of Lucifer yellow, which was less than 1% per hour. The alkaline phosphatase activity was validated using an Alkaline Phosphatase Assay Kit. The qualified monolayers were used for transport studies.