PHOSPHORYLATION OF ENDOGENOUS PROTEINS IN MYELIN OF RAT BRAIN

Abstract— The phosphorylation of endogenous proteins occurring in the myelin of rat brain was examined using the method of sodium dodecyl sulphate-polyacrylamide gel electrophoresis. Two myelin basic proteins and at least five more proteins were phosphorylated after incubation of myelin fraction in the presence of ATP + Mg²⁺. The apparent molecular weights of the proteins other than the myelin basic proteins were 120,000, 76,000, 60,000, 41,000 and 38,000, respectively. The proteins of mol wt 60,000. 41,000 and 38,000 were extracted by treatment with hydrochloric acid, whereas those of mol wt 120,000 and 76,000 were insoluble in hydrochloric acid and chloroform-methanol. Folch-Lees proteolipid protein was not found to be phosphorylated under the conditions studied. The endogenous phosphorylation of the proteins was not stimulated by adenosine 3',5'-monophosphate.     

Apolipoprotein composition of bovine lipoproteins isolated by gel filtration chromatography

1. Bovine lipoproteins were isolated from plasma by gel filtration and apolipoprotein composition determined by SDS-polyacrylamide gel electrophoresis. 2. Bovine triglyceride-rich lipoproteins contained a novel low mol. wt protein Mr = 22,000 and low mol. wt proteins that may be analogous to non-ruminant apolipoproteins A-I, A-IV, and E. 3. Apolipoprotein C appeared to be a minor constituent of bovine triglyceride-rich lipoproteins. 4. Triglyceride-rich lipoproteins contained two high mol. wt proteins of approx. Mr = 220,000 and 290,000. 5. The predominant bovine low density lipoprotein apolipoprotein was approx. Mr = 290,000, however, greater then 25 proteins were often observed between Mr = 110,000 and 370,000. 6. Bovine high density lipoprotein contained proteins analogous to apolipoprotein A-I and C apolipoproteins. 7. Differences in apolipoprotein profiles between non-lactating and lactating cows were not apparent.     

Protein phosphorylation in intact lymphocytes stimulated by Concanavalin A

The phosphorylation of proteins in intact mouse spleen lymphocytes was monitored following mitogenic activation. Little change in the autoradiographic patterns of phosphorylated protein fractionated by polyacrylamide gel electrophoresis occurred during the first 8 h after Concanavalin A (conA) treatment. The intensity of ³²P incorporation into two proteins of 135 000 and 150 000 mol. wt began to increase, relative to control cells, 10 h after conA treatment and was maximal at 50 h. This increased phosphorylation followed the rise in RNA synthesis but preceded the onset of DNA synthesis. In addition to this temporal link between enhanced phosphorylation of these proteins and the initiation of DNA synthesis, various agents which inhibited the onset of S phase also blocked the phosphorylation of both proteins. Such treatments included the displacement of conA from its surface receptors by α-methyl-mannoside (αMM), the omission of serum from the culture medium, and the presence of indomethacin. The similar time courses of phosphorylation and responses to various proliferation inhibitors supports the idea that the 135 000 and 150 000 mol. wt proteins have a common physiological function. These proteins may be involved in the progression of stimulated lymphocytes toward S phase, and their phosphorylation may be an important regulatory event in this sequence.     

Inability of the estrogen-induced uterine protein to serve as a substrate for the endogenous phosphokinase(s).

We have studied the phosphorylation of soluble proteins from uterine extracts by an endogenous protein kinase. The analysis of phosphorylation patterns by polyacrylamide gel electrophoresis did not reveal any significant difference in this respect between the soluble proteins from control or 17-beta-estradiol stimulated uteri. In both cases, three main components with mol. wt of about 120,000, 60,000 and 45,000 appear preferentially phosphorylated. Estrogen-induced protein did not coincide with any phosphorylated component, although some migrated very closely to it. This was observed whether phosphorylation was performed on uterine extract incubated with [gamma-3 2P]ATP or on intact organs incubated in the presence of 3 2Pi. We conclude that whatever the role of estrogen-induced protein, it is unlikely to be subjected to regulation through the phosphorylation process.     

A comparative binding of platinum anti-tumour compounds to plasma proteins in the rat (in vivo) and mouse (in vitro).

Plasma protein binding of 195mPt-labelled cisplatin, carboplatin and iproplatin has been studied in vivo in rat and in vitro in mouse, using both electrophoresis and trichloroacetic acid precipitation. After intravenous injection plasma clearance rates were biphasic for all 3 compounds, (t1/2 alpha, 13-17 min) but cisplatin was retained thereafter longer than the others. By 5 min, gel electrophoresis showed protein labelling with all 3 drugs but none involved low mol.wt. proteins (< 16 kDa). At 2 h a notable proportion of the protein bound platinum was associated with the latter components. There was a general resemblance between the distribution patterns of cisplatin and carboplatin whereas iproplatin showed a persistent retention of the label with time to higher mol. wt. proteins. From in vitro incubation with mouse plasma, rates of interaction respectively were cisplatin t1/2 alpha, 35 min, beta 8 h, carboplatin t1/2, 44 h and iproplatin t1/2, 104 h. By electrophoresis the protein bound fraction pattern (1 h) was again similar for cisplatin and carboplatin with virtually no binding to low mol. wt. proteins. After 24 h these were now involved to a high degree (40%). Iproplatin showed relatively marked binding to proteins of higher mol. wt. but no transfer with time to the low mol. wt. protein zone. A possible explanation is the need for in vivo metabolism for this compound as manifest in the rat. It is suggested that the significance of interaction with low mol. wt. proteins merits further investigation in relation to the antitumour and toxicological actions of these drugs.     

Genetic analysis of human lymphocyte proteins by two-dimensional gel electrophoresis:

Summary Approximately 250 phytohemagglutinin (PHA)-stimulated peripheral blood lymphocyte polypeptides from three unrelated healthy males were compared by high-resolution two-dimensional gel electrophoresis and double-label autoradiography. Comparisons by all possible pairwise combinations of [¹⁴C]leucine-labeled proteins from an individual and [³H]leucine-labeled proteins from another revealed that only three polypeptides differed qualitatively among the three individuals. The degree of variation in lymphocyte polypeptides between different individuals was similar to that in fibroblast polypeptides reported previously. Among the three variant polypeptides, two polypeptides with mol.wt. 64,000 and mol. wt. 37,000 coexisted with a polypeptide with the same molecular weight, and they showed the behavior expected of two allelic gene products separated in the isoelectric focusing dimension by charge differences. Analysis of [¹⁴C]leucine labeled peripheral blood lymphocyte proteints, from the parents of each individual, by two-dimensional gel electrophoresis indicated that the variant polypeptides with mol. wt. 64,000 and mol. wt. 37,000 in the propositus were inherited from one of his parents. The data indicate that genetic analysis of PHA-stimulated peripheral blood lymphocyte proteins is feasible by high-resolution two-dimensional gel electrophoresis in combination with double-label autoradiography and pedigree analysis.     

Sarcoplasmic reticulum. X. The protein composition of sarcoplasmic reticulum membranes

The proteins of Sarcoplasmic reticulum membranes were resolved by polyacrylamide gel electrophoresis into several fractions ranging in mol wt from 300,000 to about 30,000. The ATPase enzyme involved in Ca²⁺ transport is associated with a major protein fraction and its molecular weight based on its electrophoretic mobility on polyacrylamide gels in the presence of sodium dodecylsulfate is about 106,000. Reducing agents (β-mercaptoethanol or dithiothreitol) cause the dissociation of membrane proteins into subunits of 20,000–60,000 mol wt, which can be separated by electrophoresis or Sephadex G-150 chromatography.     

Isolation of two molecular weight variants of the mouse growth hormone receptor

GH receptors (GHRs) have been shown by affinity cross-linking to be present in late pregnant mouse liver microsomes in three forms with cross-linked mol wts of 125,000, 62,000, and 56,000. The two lower mol wt forms of the receptor were partially purified by bovine GH-affinity chromatography of 3-[(3-cholamidopropyl)dimethylammonio]-1-propane-sulfonate-solubilized extracts of late pregnant mouse hepatic microsomes. The GHRs were identified from the partially purified receptor preparation and isolated by preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The isolated GHRs had mol wts of 40,700 and 37,500, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions. Enzymatic cleavage of N-linked glycosylation from the isolated GHRs reduced their apparent mol wts to 33,600 and 30,900, respectively. Sixteen of the amino-terminal 17 amino acid residues of the two isolated receptors were sequenced and determined to be identical. One amino acid residue in each of the proteins, at position 14, could not be identified. Rabbit polyclonal antiserum was produced against the isolated GHRs. The resulting antiserum precipitated the isolated 40,700 and 37,500 mol wt proteins as well as cross-linked mouse GHRs (including the high mol wt form of the receptor). However, the antiserum did not inhibit the binding of mouse GH to either membrane bound or 3-[(3-cholamidopropyl) dimethylammonio]-1-propanesulfonate-solubilized GHRs.     

Translation of rat kidney mRNA after cadmium administration

1. Twenty-four hours after the administration of Cd2+ (11 mumol/kg body weight) to rats, the kidneys were removed and the RNA was extracted from the polysomes and used to prepare poly(A) RNA. 2. The poly(A)+ RNA was translated in rabbit reticulocyte lysates containing different labelled amino acids as precursors and the resultant proteins were separated by polyacrylamide gel electrophoresis. 3. The labelling of the proteins was similar using poly(A)+ RNA obtained from control and Cd2+ treated rats except for two proteins. 4. Regardless of labelled precursor used, proteins of mobility in sodium dodecylsulphate electrophoresis of mol. wt 50,000 contained approx twice as much radioactivity using the RNA from the kidney of treated rats. 5. Using labelled leucine, lysine, and cysteine, but not labelled phenylalanine or histidine, proteins of mobility in sodium dodecylsulphate electrophoresis of mol. wt 10,000 contained approx twice as much radioactivity using the RNA from the kidney of the Cd2+ treated rats. These results and the results following carboxymethylation of the proteins prior to electrophoresis, together with the results from co-electrophoresis of the products [125-I]-labelled liver metallothionein support the view that the poly(A)+ RNA contains kidney mRNA for metallothionein.     

Purification and partial characterization of two glycoproteins in bovine peripheral nerve myelin membrane

Two major glycoproteins of bovine peripheral nerve myelin were isolated from the acid-insoluble residue of the myelin by a procedure involving delipidation with chloroform/methanol (2:1, v/v) and chromatography on Sephadex G-200 column with a buffer containing sodium dodecyl sulfate. The separation patterns of the proteins on the gel were affected considerably by the dodecyl sulfate concentration in the elution buffer. At above 2% dodecyl sulfate concentration in the elution buffer, the glycoproteins could be separated clearly on the gel and were purified. The purified proteins, the BR protein (mol. wt. 28 000) and the PAS-II protein (mol. wt. 13 000), were homogeneous on dodecyl sulfate-polyacrylamide gel electrophoresis. The NH₂-terminal amino acids of the BR and the PAS-II proteins were isoleucine and methionine, respectively. The BR protein contained glucosamine, mannose, galactose, fucose and sialic acids and the PAS-II protein contained glucosamine, mannose, galactose, fucose and glucose. Neither the BR protein nor the PAS-II were a glycosylated derivative of a basic protein of bovine peripheral nerve myelin, a deduction based on the results of amino acid analysis. The two major glycoproteins were observed commonly in the peripheral nerve myelin of cows, pigs, rabbits and guinea pigs, using dodecyl sulfate-polyacrylamide gel electrophoresis.     

Inability of the estrogen-induced uterine protein to serve as a substrate for the endogenous phosphokinase(s)

We have studied the phosphorylation of soluble proteins from uterine extracts by an endogenous protein kinase. The analysis of phosphorylation patterns by polyacrylamide gel electrophoresis did not reveal any significant difference in this respect between the soluble proteins from control of 17-β-estradiol stimulated uteri. In both cases, three main components with mol. wt of about 120 000, 60 000 and 45 000 appear preferentially phosphorylated.Estrogen-induced protein did not coincide with any phosphorylated component, although some migrated very closely to it. This was observed whether phosphorylation was performed on uterine extract incubated with [γ-³²P]ATP or on intact organs incubated in the presence of ³²P_i.We conclude that whatever the role of estrogen-induced protein, it is unlikely to be subjected to regulation through the phosphorylation process.     

Two-dimensinal gel electrophoresis of rat liver nuclear washes,nuclear matrix,and hnRNA proteins

The proteins of rat liver cytoplasm, nuclear washes, matrix, membrane, heterogeneous nuclear (hn)RNA proteins and chromatin were examined by two-dimensional gel electrophoresis. The inclusion in the gels of six common protein standards of carefully selected molecular weight and isoelectric point allowed us to clearly follow the distribution of specific proteins during nuclear extraction. In the nuclear washes and chromatin, we observed five classes of proteins: (a) Exclusively cytoplasmic proteins, present in the first saline-EDTA wash but rapidly disappearing from subsequent washes; (b) ubiquitous proteins of 75,000, 68,000, 57,000, and 43,000 mol wt, the latter being actin, found in the cytoplasm, all nuclear washes and the final chromatin pellet; (c) proteins of 94,000, 25,000, and 20,500 mol wt specific to the nuclear washes; (d) proteins present in the nuclear washes and final chromatin, represented by species at 62,000, 55,000, 54,000, and 48,000 mol wt, primarily derived from the nuclear matrix; and (e) two proteins of 68,000 mol wt present only in the final chromatin. The major 65,000- 75,000-mol wt proteins seen by one-dimensional gel electrophoresis of nuclear matrix were very heterogeneous and contained a major acidic, an intermediate, and a basic group. A single 68,000-mol wt polypeptide constituted the majority of the membrane-lamina fraction, consistent with immunological studies indicating that a distinct subset of matrix proteins occurs, associated with heterochromatin, at the periphery of the nucleus. Actin was the second major nuclear membrane-lamina protein. Two polypeptides at 36,000 and 34,000 mol wt constituted 60% of the hnRNP. Approximately 80% of the mass of the nonhistone chromosomal proteins (NHP) from unwashed nuclei is contributed by nuclear matrix and hnRNPs, and essentially the same patterns were seen with chromatin NHP. The concept of NHP being a distinct set of DNA- bound proteins is unnecessarily limiting. Many are derived from the nuclear matrix or hnRNp particles and vary in the degree to which they share different intracellular compartments.     

Phosphorylated proteins from anuran intestinal microvilli membranes--I. Relations with alkaline phosphatase

The degree of phosphorylation of intestinal microvilli membrane proteins in an adult amphibian, Rana esculenta, was investigated under various experimental conditions. The microvilli protein phosphorylation rate rapidly increases during the first 4 min of incubation in a medium containing [gamma-32P]ATP. This increase is slower afterwards. Cyclic nucleotides (cyclic AMP, cyclic GMP) and sorbitol do not modify the microvilli protein phosphorylation rate. On the contrary, this phosphorylation rate significantly decreases in the presence of L-lysine, when its concentration in the incubation medium is greater than 25 mM. The time course of phosphorylation confirms the inhibitory effects of L-lysine (100 mM). The microvilli membrane proteins were distinguished by polyacrylamide gel electrophoresis. In heated samples, electrophoresis followed by an radioautograph systematically reveals the existence of a very phosphorylated protein with a mol. wt of 86 kDa. The phosphorylation of this protein is partially inhibited by L-lysine (100 mM). The very phosphorylated protein could be the monomer of alkaline phosphatase. The dimer (170 kDa) is visualized on electrophoretograms by its catalytic activity. In mammals, several authors have established a correlation between phosphorylation of the microvilli membrane proteins and the intensity of intestinal calcium absorption. Such a control is presently being investigated in adult Rana esculenta.     

Endogenous proteolytic activity and constituent polypeptide chains of sheep and pig 19 S thyroglobulin.

Porcine and ovine 19-S thyroglobulins prepared from frozen glands in several buffers using slice extraction or homogenization, ammonium sulfate precipitation and DEAE-cellulose chromatography or Sepharose 6B gel filtration were contaminated with protease activity of pH optima 4.5 and 8.6, as shown by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Optimum temperatures of autodigestion were 37 degrees C at pH 4.5 and 25 degrees C at pH 8.6. Thyroglobulins prepared from unfrozen glands pH 7.2 in 0.1 M sodium phosphate using slice extraction, ammonium sulfate precipitation and Sepharose 6B gel filtration were devoid of acid proteolytic activity but still underwent autodigestion at pH 8.6. Diisopropylfluorophosphate was a potent inhibitor of the alkaline protease activity of ovine thyroglobulin preparations. In contrast to thyroglobulin obtained from frozen glands the proteins purified from fresh unfrozen glands at pH 7.2 only showed the 19-S and the 12-S species by electrophoresis in sodium dodecyl sulfate polyacrylamide gels. Very few bands migrating faster than 12-S were visible. After full reduction and S-alkylation of porcine and ovine thyroglobulins, no qualitative changes were observed in the gel electrophoresis pattern as compared to the unmodified proteins. Species of apparent mol. wt. corresponding to the native 12 S were the major component, strongly suggesting a mol. wt. of about 330 000 for the elementary peptide chains of pig and sheep thyroglobulins.     

Mapping of fish myosin light chains by two-dimensional gel electrophoresis

1. Myosins were prepared from the ordinary muscle of 16 fish species as well as from rabbit fast muscle, and light chain subunits [alkali light chains A1, A2 and DTNB (5,5'-dithio-bis-2-nitrobenzoate) light chain] were separated on two-dimensional gel electrophoresis in combination with isoelectric focusing and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. 2. A1 light chains showed mol. wts ranging from 21,000 to 22,900 and isoelectric points ranging from 4.51 to 4.62. DTNB light chains were spotted in a narrow area, with a mol. wt range of 16,800-17,600 and an isoelectric point range of 4.48-4.55. On the other hand, A2 light chains were most species-specific, with a mol. wt range of 14,000-19,500 and an isoelectric point range of 4.31-4.46. 3. It was suggested that the lower species-specificity in A1 as opposed to A2 is accounted for by the addition of an N-terminal peptide ("difference peptide") in the former. The properties and possible role of this peptide are discussed.     

In vitro phosphorylation of phosphatidylethanolamine N-methyltransferase by cAMP-dependent protein kinase: lack of in vivo phosphorylation in response to N6-2'-O-dibutryladenosine 3',5'-cyclic monophosphate

Phosphorylation of rat liver phosphatidylethanolamine (PE) N-methyltransferase by cAMP-dependent protein kinase was investigated. The 18 kDa methyltransferase was found to be phosphorylated in vitro by cAMP-dependent protein kinase on a serine residue. The stoichiometry of phosphate incorporation reached a maximum of 0.25 mol phosphate/mol methyltransferase at 30 min. Resolution of the phosphorylated methyltransferase by two-dimensional gel electrophoresis showed that two isoproteins were substrates. Phosphorylation of the purified PE N-methyltransferase for up to 1 h had no effect on the methylation of PE, PMME or PDME. To test for in vivo phosphorylation, isolated rate hepatocytes were exposed to 0.5 mM N6-2'-O-dibutryladenosine 3':5'-cyclic monophosphate (DiB-cAMP) and the phosphorylation state of microsomal proteins evaluated by two-dimensional gel electrophoresis, nitrocellulose blotting and autoradiography. The same nitrocellulose blots were probed with a rabbit anti-PE N-methyltransferase antibody, immunochemically stained and aligned with the autoradiogram. No phosphorylated proteins co-migrated with the methyltransferase under non-phosphorylating conditions, or when hepatocytes were exposed to the cAMP analogue for up to 2 h. Oddly, DiB-cAMP increased both PE- and PMME-dependent activity in isolated microsomes, but decreased PE to PC conversion measured in intact hepatocytes. The results indicated that PE N-methyltransferase is poorly phosphorylated by cAMP-dependent protein kinase in vitro, and is not phosphorylated in intact hepatocytes treated with a cAMP analogue.     

A comparison of the major surfactant-associated proteins in different species

We examined the major surfactant-associated proteins in a number of species by using two-dimensional gel electrophoresis, protein blotting and immunostaining. All species have a 30,000 to 35,000 mol. wt protein group consisting of multiple isoforms with isoelectric points ranging from pH 4.4 to 5.6. The techniques used in this study have resolved three component subgroups within the 35 K group. A group of proteins at 60,000-65,000 mol. wt has also been consistently identified. We conclude that remarkable similarity exists among the major surfactant-associated proteins from various mammals with regard to isoelectric points, molecular weights and antigenic sites.     

The Partial Characterization of the Major Seed Storage Proteins in Arabidopsis thaliana L.

This study was aimed at the characterization of the major storage proteins in Arabidopsis thaliana. Two major protein fractions, i.e., the fraction Ⅰ and Ⅱ proteins, were isolated from the extract of mature seeds of this plant by molecular seive gel filtration chromatography. Various polyacrylarnide gel electrophoretic techniques were used to study the properties and polypeptide compositions of these two protein fractions. In was shown that during the SDS gel electrophoresis, fraction Ⅰ protein was separated into 6 major bands with the mol. was. of 34, 31, 29, 28 and 19-20 kD, respectively, whereas Fraction Ⅱ protein migrated as 3 low mol. wt. bands (10-12 kD) on the same gel. Non-denaturing native gel electrophoresis revealed that fraction Ⅰ was a neutral protein and Fraction Ⅱ was a positively charged basic protein with an isoelectric point (pI) higher than 8.8. Fraction I protein was further separated into at least 16 polypeptides in isoelectric focusing/SDS two-dimensional gel electrophoresis, i.e. each SDS band contained 3-4 polypeptides with the same mol. wt. but different pis. This suggested a more complex polypeptide composition of this protein. The properties of fraction Ⅰ and Ⅱ proteins were in good accordance with that of the 12s and 1.7s storage globulins in seeds of many other dicotyledonous plants, and therefore had been characterized as the two major seed storage proteins in this species. These two storage globulins were shown to be accumulated within a defined period during the late stage of seed development (12-14 DAF) and became predominant protein components in mature seeds. In the mean time, a few points in relation to the polypeptide composition and subunit molecular configuration of the 12s globulin were noted.     

The characterization of the whey proteins of guinea-pig milk: The isolation and properties of α-lactalbumin

1. The whey proteins of guinea-pig milk were examined by electrophoresis on paper, cellulose acetate, starch gel and polyacrylamide gel. 2. Two major proteins were detected, one of which was identified as blood serum albumin. 3. The major whey protein was isolated by CM-cellulose chromatography and on columns of Sephadex G-100. 4. The amino acid composition of the protein, taken in conjunction with its other properties, indicated that the major whey protein in guinea-pig milk is homologous with cow α-lactalbumin and that β-lactoglobulin is absent from guinea-pig milk. 5. Guinea-pig α-lactalbumin, which was obtained crystalline, had mol.wt. 15800, N-terminal lysine and C-terminal glutamine.     

Isolation and preliminary characterization of epithelial-specific messenger ribonucleic acids and their products during embryonic tooth development.

Experiments were designed to identify and characterize tissue-specific proteins involved in the process of tooth organogenesis. Epithelial and mesenchymal proteins were extracted from intact molar organs or mechanically separated tissues obtained from 25-day New Zealand White rabbit embryos. Labelling experiments with [35S]methionine followed by radioautography or gel electrophoresis and fluorography showed the presence of label only in epithelial proteins. Most of these proteins range from 43 000 mol.wt. and higher, except for one band of approx. 16 000 mol.wt. A mRNA fraction of 16--26S was isolated by ultracentrifugation on sucrose gradients. When translated in a reticulocyte-lysate cell-free system, the mRNA obtained from intact molar organs resulted in the synthesis of three proteins, of mol.wts. 65 000, 58 000 and 43 000. A similar mRNA fraction obtained from dental-pulp mesenchyme gave only the 43 000-mol.wt. protein, indicating that the 65 000- and 58 000-mol.wt. proteins are derived from epithelial cells.