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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The influence of quercetin on electron transport and photophosphorylation of pea isolated chloroplasts with methylviologen and NADP+ has been studied. Quercetin inhibits ATP synthesis and phosphorylating electron transport but does not affect the basal electron transport in the presence of methylviologen. In view of these data and because of the increase of the proton uptake by chloroplasts in the presence of quercetin we consider it as an inhibitor of energy transfer. Under conditions of NADP+ photoreduction quercetin acts also as an inhibitor of electron transfer, interacting with ferredoxin, though a complete inhibition of electron transfer has not been observed. This last phenomenon may be of importance for the understanding of the detailed mechanism of NADP+ reduction by chloroplasts.
Mol Biol (Mosk)
PMID:[Inhibition of electron transport and photophosphorylation in chloroplasts by quercetin]. 2 2

Using gel filtration chromatography, we find a single peak of deoxythymidine phosphorylating activity in Chlamydomonas reinhardti. This activity has characteristics of a thymidine kinase, in that (1) it will utilize ATP (or dATP) or CTP (or dCTP) as phosphoryl donor, but not AMP or phenyl phosphate, and (2) it is inhibited by dTTP (and less so by dTDP, dUTP, and dUDP) but is unaffected by 3'-5' cyclic AMP. Partially purified chlamydomonas thymidine kinase has a pH optimum near 8.5, and a molecular weight of 80,000 to 85,000 daltons. Kinetic studies indicate a ping-pong mechanism with a Km for thymidine of 1.5 x 10(-7) moles per liter. 5-Bromo- and 5-fluorodeoxyuridine, and to a lesser degree deoxyuridine, are competitive inhibitors, but significant phosphorylation of these nucleotides could not be demonstrated in vitro by thymidine kinase. While thymidine is phosphorylated to dTMP by crude Chlamydomonas extracts, greater than 80% of the product formed by the partially purified enzyme is dTTP. Further, the gel filtration elution position of the single deoxythymidylate kinase activity present in cell extracts coincides with that of thymidine kinase. These results suggest that a multifunctional enzyme, rather than three separate phosphorylating activities, may be responsible for dTTP formation.
Mol Gen Genet 1979 Nov
PMID:Characterization of thymidine kinase and phosphorylation of deoxyribonucleosides in Chlamydomonas reinhardti. 4 38

Considerable progress has been made in recent years in our understanding of the phosphorylating apparatus in mitochondria, chloroplasts, and bacteria. It has become clear that the structure and the function of the ATP synthesizing apparatus in these widely divergent organisms is similar if not virtually identical. The subunit composition of F1, its molecular architecture, the location and function of substrate binding sites, as well as putative control sites, understanding of the component parts of the oligomycin-sensitive ATPase complex, and the role of these components in the function of the complex all are under active investigation in many laboratories. The developing information and the new insights provided have begun to permit experimental approaches, at the molecular level, to the mode of action of the ATPase in electron-transport-coupled ATP synthesis.
Adv Enzymol Relat Areas Mol Biol 1979
PMID:Mitochondrial ATPase. 16 56

1. Glucokinase is one of four glucose phosphorylating enzymes present in rat liver. Its distinctive features are a high K-m for glucose (high-K-m isozyme) and a rather narrow substrate specificity. In contrast, the other three enzymes, collectively called hexokinases or low-K-m isozymes, exhibit low K-m values for glucose and a wider substrate specificity. 2. Glucokinase is present in the liver os mammals (with some exceptions), amphibians and lower reptiles; It is absent from higher reptiles and birds. The presence or absence of glucokinase may represent an evolutionary adaptation to feeding habits and other physiological peculiarities. Differences in the immunological behavior and in the kinetic parameters of glucokinases from different taxa suggest the operation of divergent evolution. 3. The levels of glucokinase in rat liver depend strictly on the supply of carbohydrate in the diet. Glycogen phosphorylase and glycogen synthetase behave similarly, whereas other carbohydrate-metabolizing enzymes depend on the provision of either protein or protein plus carbohydrate. Glucokinase decays with a half-life of 33 hr when rats are starved or fed a carbohydrate-free diet, and is induced by the administration of glucose. The adaptive character is not exhibited by all mammals, indicating evolutionary discrimination within the same class and even within the same single order Rodentia. Enzyme adaptation in the liver may partially explain the condition known as 'hunger diabetes'. 4. The endocrine system plays a paramount role in glucokinase adaptation, since insulin is essential for glucose-dependent glucokinase induction and, on the other hand, glucagon, catecholamines and cyclic AMP prevent the induction. Glucocorticoids and some pituitary hormones modulate the rate of induction. The mechanisms underlying the hormonal regulation of glucokinase levels are not well known. 5. The variations in liver glucokinase correspond to changes in the amount of enzyme protein as assessed by immunochemical titration. This fact agrees with the effects of inhibitors of protein synthesis on glucokinase induction. 6. An antiserum against rat glucokinase reacts with the enzyme from mammals and turtles but not with the amphibian enzyme. It does not react with low-K-m hexokinases from different sources. 7. The saturation function for glucose is sigmoidal in mammalian and amphibian glucokinases but not in glucokinase from lower reptiles. The Hill's coefficient is very constant with values about 1.6. The K0.5 (concentration for half saturation) values in the different species studied vary between 1.5 and 8 mM. These kinetic parameters may be considered as another adaptive feature aimed to give maximal efficiency to the liver uptake of glucose at the changeable concentrations in the blood resulting from variations in the amount of dietary glucose.
Mol Cell Biochem 1975 Feb 28
PMID:Adaptive character of liver glucokinase. 16 20

The influence of a specific histone kinase, phosphorylating lysine-rich histone F1, F2a2, F2b, on the physico-chemical properties of the chromatin in the whole undestroyed fixed cell, has been investigated. It was found that the exogenous histone kinase penetrates into the nuclei of the undestroyed fixed cells and into the isolated unfixed nuclei and changes the physico-chemical properties of the chromatin there, bringing about an increase in binding of a basic dye acridine orange and a decrease in its stability to heat.
Mol Biol Rep 1975 Oct
PMID:Influence of a specific histone kinase on the physico-chemical properties of chromatin in situ. 17 82

The influence of a specific histone kinase, phosphorylating lysin-rich histone H1, H2a, H2b on the physico-chemical properties of chromatin from hepatocytes of normal and hepatectomized guinea pigs has been investigated. A cytochemical method has been used which permits to obtain information about the physico-chemical properties of the chromatin in situ, i.e. without its isolation. This approach allows us to evaluate changes in chromatin properties in cell cultures as well as in the intact organism. It is found that the specific histone kinase changes the properties of chromatin in non-dividing cells bringing about an increase of acridine orange binding to the level characteristic for hepatocytes after partial hepatectomy. At the same time the chromatin properties in activated hepatocytes are not changed under the action of the histone kinase. It is concluded that the specific histone kinase, phosphorylating lysine-rich histones can play an important role in the course of chromatin activation in cells stimulated to proliferation.
Mol Biol (Mosk)
PMID:[Influence of histone kinase phosphorylating lysine-rich histones, on the physico-chemical properties of normal hepatocyte chromatin and after partial hepatectomy]. 22 34

When strains of Saccharomyces cerevisiae carrying a single glucose-phosphorylating enzyme such as hexokinase Pl or hexokinase P2 or glucokinase, are subjected to the selection pressure against the toxic sugar 2-deoxyglucose, the majority of survivors are mutants lacking the respective enzymes. All the 2-deoxyglucose-resistant segregants recovered from backcrosses of these mutants to a wild type strain are glucose-negative and all the sensitive ones are glucose-positive. The hexokinase mutations are located in the same complementation groups as defined by the structural genes of hexokinase P1 and hexokinase P2. No interallelic complementation has been observed either in hexokinase P1 or in hexokinase P2 amongst a total of 4 X 64, and 5 X 60 different combinations of independent mutants at the hxk1 and hxk2 loci respectively. There appears to be neither a common genetic regulator controlling two or more of these glucose-phosphorylating enzymes nor a sugar carrier that can be dispensed with.
Mol Gen Genet 1977 Dec 09
PMID:Resistance to 2-deoxyglucose in yeast: a direct selection of mutants lacking glucose-phosphorylating enzymes. 34 Sep 26

At least two protein kinase activities are bound to the rat liver mitochondrial membranes. Both activities are found to phosphorylate, besides endogenous proteins tightly bound to the membrane structures, also exogenous phosphoproteins such as casein and phosvitin. However one is able to phosphorylate both casein-bound serine and threonine residues, while the other is phosphorylating almost only serine residues.
Mol Cell Biochem 1976 Nov 30
PMID:Phosphorylation of casein by mitochondrial protein kinase(s). 100 99

Glucose uptake by brown adipose tissue, measured following deoxyglucose injection in vivo, was increased by 6- and 11-fold following 2 and 14 days of cold exposure, respectively. To look for the possible mechanism of these modifications, the glucose transporter Glut 4 has been characterized at the protein and mRNA levels in brown adipose tissue, skeletal muscle and white adipose tissue following cold acclimation. Crude membranes were prepared from those tissues, and Glut 4 was studied by Western blot analysis. In brown adipose tissue, the total Glut 4 amount was increased by 52 +/- 7% and by 104 +/- 12% following 2 and 14 days of cold exposure, respectively. By contrast, in white adipose tissue of 14-day-cold-exposed mice the total Glut 4 content was decreased by 42 +/- 5%. However, Glut 4 concentration, expressed per mg of membrane protein, was unchanged in both brown and white adipose tissues following cold exposure, since the membrane protein content increased in brown but decreased in white adipose tissue. No modification in Glut 4 content was observed in skeletal muscle from cold-exposed mice. Total RNA were prepared and analyzed for Glut 4, glyceraldehyde phosphate dehydrogenase (GAPDH) and actin. Glut 4 and GAPDH mRNA were increased 2-fold in brown adipose tissue from cold-exposed mice, while actin mRNA content was unmodified. Glut 4 mRNA content was not changed in white adipose tissue and skeletal muscle from cold-exposed mice. Our results suggest that Glut 4 expression is differently modulated in the three insulin-responsive tissues during cold acclimation.
Mol Cell Endocrinol 1992 Nov
PMID:Effect of cold acclimation on the expression of glucose transporter Glut 4. 130 80

p42/microtubule-associated protein kinase (p42mapk) is activated by tyrosine and threonine phosphorylation, and its regulatory phosphorylation is likely to be important in signalling pathways involved in growth control, secretion, and differentiation. Here we show that treatment of quiescent 3T3 cells with diverse agonists results in the appearance of an activity capable of causing the in vitro phosphorylation of p42mapk on the regulatory tyrosine and to a lesser extent on the regulatory threonine, resulting in enzymatic activation of the p42mapk. This p42mapk-activating activity is capable of phosphorylating a kinase-defective p42mapk mutant, thus confirming its activity as a kinase.
Mol Cell Biol 1992 May
PMID:Growth factor-induced activation of a kinase activity which causes regulatory phosphorylation of p42/microtubule-associated protein kinase. 131 51


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