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J G Georgatsos

Publications and source records attributed to J G Georgatsos.

At least 19 recordsLinked to original sources
PubMed2001

Barley beta-galactosidase: structure, function, heterogeneity, and gene origin.

Barley (Hordeum vulgare) beta-galactosidase is composed of a large (45 kDa) and a small (33 kDa) polypeptide. N-terminal sequencing of the polypeptides and antibody reactivity data place the barley enzyme and heterodimeric plant beta-galactosidases from jack bean, maize, and wheat in family 35 of the glycosyl hydrolases. Sequence analysis indicates the existence of a subfamily of genes coding for polypeptide precursors that are cleaved to produce the two subunits in heterodimeric beta-galactosidases. The heterogeneity of the barley holoenzyme is related, but not restricted, to the N-glycosylation of the small polypeptide. Both polypeptides are essential for the catalytic activity of the enzyme.

Amino Acid Sequence↗
PubMed1999

Purification and characterization of a dimer form of the cAMP-dependent protein kinase from mouse liver cytosol.

A protein kinase that phosphorylates histones and polysomal proteins was partially purified from mouse liver cytosol. The active enzyme has a molecular mass of 100 kDa and a phosphorylatable subunit of 54 kDa. Biochemical as well as immunological data suggest that the enzyme is a heterodimer composed of the catalytic subunit of cyclic AMP-dependent protein kinase and the RII regulatory subunit. This RC form does not seem to dissociate upon activation with 3', 5' cyclic AMP and exhibits identical specificity as the classical cAMP-dependent protein kinase (2.7.1.37). The enzyme is affected by the 3', 5' cyclic phosphates of adenosine mainly, but also of guanosine, uridine and cytidine in a substrate-dependent manner. Cyclic nucleotides slightly stimulate phosphate incorporation into histones, while phosphorylation of polysomal proteins in intact polysomes is dramatically increased. The substrate- specific stimulatory effects of 3', 5' cyclic nucleotides are due to repression of the inhibition exerted upon the reaction, by negatively charged macromolecules such as RNA, DNA and to a lesser extent heparin.

Animals↗
PubMed1994

Barley beta-glucosidase: expression during seed germination and maturation and partial amino acid sequences.

Unlike most of the hydrolytic enzymes that participate in endosperm mobilization, beta-glucosidase of barley (Hordeum vulgare) seeds does not increase during germination, even in the presence of exogenously added gibberellic acid. However, the germination process affects the physical properties of beta-glucosidase in terms of charge and apparent molecular weight. Analysis of developing barley grains shows that the enzyme is synthesized two weeks before maturation and is stored in the endosperm of the dry dormant seed. Partial amino acid sequencing of the purified beta-glucosidase demonstrates significant similarity between the barley enzyme and beta-glycosidases that belong to family 1 of glycosyl hydrolases.

Amino Acid Sequence↗
PubMed1992

Ribonucleases of diverse specificities in rabbit brain nuclei.

A salt extract of rabbit brain nuclei contains three endoribonucleases, designated RNases Y, A and R, which produce acid-soluble products when incubated at near-neutral pH in the absence of metal ions. RNases Y and A yield products with the monoesterified phosphate at the 3' position, through 2',3'-(cyclic)phosphate intermediates. Oligonucleotides terminating with a 2',3'-(cyclic)phosphate are the end-products of the action of RNase R. Double-stranded substrates are highly resistant to the action of all enzymes. On the basis of limited hydrolysis of end-labelled 5S RNA, the three enzymes differ in their preference for the susceptible phosphodiester bond. Thus, RNase Y hydrolyses preferentially the YpN bond, RNase A the ApN bond and RNase R the RpU bond where R is guanosine in most cases. The advantages and disadvantages of using homopolyribonucleotides and dephosphorylated dinucleotides and trinucleotides in determining various aspects of the specificity of RNases are discussed.

Animals↗
PubMed1990

Concentration-dependent effects of natural polyamines on peptide chain initiation and elongation in a cell-free system of protein synthesis.

Spermidine and spermine at submillimolar concentrations stimulate the rate of incorporation of amino acid into protein in a cell-free system, directed either by endogenous or exogenous mRNA (TMV, globin). The stimulatory effects of these polyamines are exerted at both the stages of initiation and elogation and are more pronounced in the case of TMV or globin mRNA, amounting to approximately 2.3-fold stimulation over the polyamine-free system. The number of polysomes and the polysome-associated radioactivity increase approximately 2-fold in the presence of spermine. Synthesis of large polypeptides is a characteristic feature of the stimulatory event. However, elevated concentrations of spermidine and spermine strongly inhibit amino acid incorporation into protein. Inhibition is manifest at the stage of peptide elongation. In the case of endogenous mRNA the addition of an excess of polyamines results in a non uniform inhibition of amino acid incorporation. A most interesting finding is that, with increasing concentrations of polyamines, the intensity of four bands with Mr values of 63000, 44000, 15500 and 12500 respectively, increases or leastwise remains constant while others fade, indicating differential translation of proteins in the presence of polyamines.

Animals↗
PubMed1990

A guanyloribonuclease of mouse liver cytosol.

The acid RNase activity of mouse liver cytosol has been resolved into two different enzymes named acid RNase I and acid RNase II respectively. Acid RNase I is a typical pancreatic-type enzyme hydrolyzing CpN and UpN bonds. Acid RNase II, however, hydrolyzes GpN bonds in non-hydrogen-bonded regions of the substrate.

Animals↗
PubMed1990

Inhibition of protein synthesis by acetyl-coenzyme A in a cell-free system: possible involvement of protein acetylation in the regulation of translation.

Acetyl-coenzyme A (CoASAc) inhibits the rate of incorporation of amino acid into protein in a cell-free system of mouse liver. The effect is more pronounced when exogenous mRNA (tobacco mosaic virus or globin mRNA) rather than endogenous messages are used. Micromolar concentrations of the cofactor block initiation, while millimolar concentrations cause a more general inhibition of the translation process, that affects, in addition, the elongation step. Inclusion of [1-14C]acetyl-CoA in a protein synthesis reaction mixture results in a very rapid and selective labelling of a protein of 200 kd of the 'pH 5' fraction. The possible involvement of the acetylating event in the regulation of protein synthesis is discussed.

Acetyl Coenzyme A↗
PubMed1988

Lactose-hydrolyzing beta-glycosidases of barley meal.

A beta-glucosidase and a beta-galactosidase were purified to homogeneity from barley meal. The beta-glucosidase is a single basic polypeptide (pI greater than 8.5) with an Mr of 53,000 acting optimally at pH 4.5-5.0. The beta-galactosidase is composed of two subunits with an Mr of 42,000 and 33,000, respectively, and is acidic in nature (pI less than 5.7). Both enzymes are able to hydrolyze lactose with Michaelis constants lower than the concentration of this sugar in milk whey. Consequently, barley seems to be an inexpensive source of lactose-splitting enzymes.

Galactosidases↗
PubMed1988

Purification and properties of a membrane-bound L-asparaginase of Tetrahymena pyriformis.

L-Asparaginase activity reaches maximal values at the stationary phase of growth of Tetrahymena pyriformis and fluctuates upon the growth conditions and the composition of the medium. Most of the L-asparaginase activity (80%) is associated with the endoplasmic reticulum, and the remaining with the pellicles. Detergents either alone or in combination with NaCl up to 0.5 M concentration failed to solubilize L-asparaginase. Solubilization can be accomplished by means of either the chaotropic agents KSCN and NaClO4, or 0.1 M sodium phosphate buffer pH 8.0, following pretreatment of the particulates with 2% w/v Triton X100. L-Asparaginase has been purified to near homogeneity by hydrophobic and gel filtration chromatography. The native enzyme has a relative molecular weight of 230,000. It is a multiple subunit enzyme, with subunit size of 39,000. Its isoelectric point is at pH 6.8. It acts optimally at pH 8.6 with a Km of 2.2 mM. It does not hydrolyse L-glutamine and its reaction is inhibited competitively by D-aspartic acid and D-asparagine as well as by L-asparagine analogues with substituents at the beta position.

Animals↗
PubMed1988

A high-yield cell-free system of protein synthesis of mouse liver.

1. A fractionated cell-free system of protein synthesis has been developed from mouse liver. It is composed of polysomes, "pH 5" fraction, Mg2+, K+, ATP and a ATP generating system. 2. It operates optimally at 30-37 degrees C, in the presence of 4 mM MgCl2 and 90 mM KCl. 3. Spermine is highly inhibitory, while spermidine shows a bimodal action, in that submillimolar concentrations stimulate, while millimolar concentrations inhibit protein synthesis. 4. Both spermine and spermidine show an interesting selectivity, in that, even though they inhibit incorporation of amino acids into most proteins, they stimulate incorporation into a few proteins. 5. The system can be rendered mRNA-dependent, either by preincubation or by treatment with micrococcal nuclease. In both cases globin mRNA as well as TMV RNA are faithfully translated. 6. Compared to other published mammalian fractionated cell-free systems, the mouse liver system is more efficient by approximately one order of magnitude, since the rate of incorporation of leucine per min is 30 pmol/mg protein or 435 pmol/mg RNA or 1 mol/mol ribosomes.

Animals↗
PubMed1987

Specificity and other properties of three ribonucleases of Tetrahymena pyriformis.

Three ribonucleases, RNase I, RNase II and RNase III, were purified from the 109,000 X g supernate of detergent-treated Tetrahymena pyriformis strain W. RNases I and II act optimally at pH 5.5-6.0 and are inhibited by increasing concentrations of salts of monovalent cations. RNase III acts optimally at pH 7.5 and is activated 1.5-fold by millimolar concentrations of ZnSO4 and 5-fold by 50 mM KCl. RNases II and III are activated approximately 100% in the presence of 3 M and 5 M urea respectively. All enzymes are heat-sensitive and acid-resistant. They are endonucleases forming 2',3'-cyclic products. Their base specificity, as tested against ribosomal RNAs of known sequence, is as follows: RNase I hydrolyzes preferentially YpN and secondarily GpN bonds, RNase II is highly specific for RpN bonds, though the preparation can also hydrolyze the UpU sequence. Finally the principal targets of RNase III are YpR sequences and secondarily YpY sequences. A shorthand visualization of base specificity of nucleases in the form of right isosceles triangles is presented. The triangles are constructed by subdividing each of the two perpendicular sides in as many units as the maximum number of times the most abundant dinucleotide appears in all substrates employed and plotting the frequency of hydrolysis of each dinucleotide sequence by the enzyme under study. The proximity of each dinucleotide sequence to the hypotenuse or to one of the perpendicular sides is indicative of its susceptibility or resistance to the enzyme's action.

Animals↗
PubMed1987

Protein phosphorylation patterns in human blood serum.

Phosphorylation of human blood serum proteins by endogenous kinases shows biphasic kinetics. During the early phase mostly beta-globulins are phosphorylated, while during the late phase alpha-globulins are also phosphorylated. In SDS-polyacrylamide gel electrophorograms, 32P-labelled peptides of 6, 14.3, 20, 23, 34, 37 and 40 kilodaltons were detected. No differences in phosphorylation pattern were observed in the sera of patients with various pathological conditions, under the experimental conditions employed.

Electrophoresis, Polyacrylamide Gel↗
PubMed1985

Purification and properties of ornithine decarboxylase from Tetrahymena pyriformis.

In Tetrahymena pyriformis, ornithine decarboxylase (L-ornithine carboxy-lyase, EC 4.1.1.17) activities are present in the cytosolic and nuclear fractions and reach maximal values in the middle and late log phases of growth, respectively. The two activities have been purified to homogeneity by ammonium sulfate fractionation (20-45%), anion-exchange chromatography (DEAE-Bio-Gel A), gel-filtration (Sephadex G-150 and Sephadex G-100 superfine) and hydrophobic chromatography (Phenyl-Sepharose). Both the crude and the purified enzyme preparations are inactivated irreversibly by alpha-difluoromethylornithine, a suicide inhibitor of mammalian ornithine decarboxylase. The enzyme preparations from the nucleus and cytosol each showed a single band on polyacrylamide gel electrophoresis under native and denaturing conditions and on acrylamide gel electrofocusing. Both activities show the same pH optima (8.6) isoelectric point (5.3), molecular weight (64 000) and Kmorn (4.7 microM). The Km for L-lysine is 0.5 mM. The two activities also cross-react with acidic antizyme extracted from E. coli mutant MA 255. Based on the physicochemical properties, one can safely conclude that cytosolic and nuclear activities reside on the same protein molecule.

Animals↗
PubMed1984

Purification and properties of three cytosolic ribonucleases of mouse liver.

The ribonucleolytic activity of mouse liver cytosol is due to at least three different enzymes, whose purification is reported. Two of these enzymes, an alkaline and a neutral RNase, have specificities practically identical with that of pancreatic RNase. The third enzyme, an acid RNase, is highly specific for NpU bonds where N is A, G or C and also cleaves ApG bonds provided they are part of a GpApG sequence and preferentially a GpApGpA repeat.

Animals↗
PubMed1984

Chloramphenicol inhibits hemoglobin synthesis in blood islands of young chick blastoderm.

Hemoglobin (Hb) synthesis is reduced by 1.5 to 12.4 X 10(-4) M chloramphenicol (CAP) in chick blastoderms at head process and 4-somite stages. Chloramphenicol at 18.6 X 10(-4) M results in decrease of amino acid uptake and incorporation into protein, and inhibits Hb formation completely. However, this effect can be overcome partially when blastoderms are removed from CAP-containing to plain culture medium. The morphological appearance, protein content, and behaviour in amino acid uptake and incorporation of control and CAP-treated blastoderms at the time Hb first makes its appearance can be correlated and seem to reflect changes occurring in the vascular area during the time of blood island organization and subsequent massive Hb synthesis in the simple culture system employed.

Amino Acids↗