Specific enzymic methylation of an arginine in the experimental allergic encephalomyelitis protein from human myelin

Studies on protein methyltransferase in human cerebrospinal fluid

Protein methyltransferases, rich in most mammalian brains, were studied in human cerebrospinal fluid (CSF). Among several well-characterized groups of methyltransferases, protein methylase I (S-adenosylmethionine:protein-arginine N-methyltransferase, EC 2.1.1.23) was found in significant amounts in human CSF samples. Both myelin basic protein (MBP) -specific and histone-specific protein methylase I activities were observed, the latter being generally higher in most CSF. S-Adenosyl-L-homocysteine, a potent product inhibitor for the methyltransferase, inhibited approximately 90% of MBP-specific protein methylase I activity at a concentration of 1 mM. The optimum pH of the MBP-specific protein methylase I was found to be around 7.2. Identity of exogenously added MBP as the methylated substrate for CSF enzyme was confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. An amino acid analysis of the [methyl-3H]protein hydrolysate showed two major radioactive peaks cochromatographing with monomethyl- and dimethyl (symmetric)-arginine. Human CSF contained relatively high endogenous protein methylase I activity (activity measured without added substrate protein): The endogenous substrate can be immunoprecipitated by antibody raised against calf brain MBP. Finally, CSF from several neurological patients were analyzed for protein methylase I, and the results are presented.

An amino-terminally extended and post-translationally modified form of a 25kD basic fibroblast growth factor

Basic fibroblast growth factor (bFGF) is a heparin-binding angiogenic polypeptide mitogen. bFGF proteins characteristically have a molecular weight of 18,000 which is consistent with the predicted primary translation product of 155 amino acids from the cDNA. More recently, higher molecular weight forms of bFGF have been identified but their structural relationship to the commonly known 18kD bFGFs has not been established. We now show that a 25kD bFGF purified from guinea pig brain tissue is an N-terminally extended and post-translationally modified form of the growth factor. Although the exact nature of the post-translational modifications has not been determined, circumstantial evidence suggests that they may be methylated arginines.

Human T lymphocyte response to myelin basic protein: selection of T lymphocyte lines from MBP-responsive donors

The goal of this study was to delineate the importance of blood T lymphocyte responses to several myelin basic protein (MBP) preparations in the ultimate selection of MBP-specific T lymphocyte lines. Proliferation responses to human myelin basic protein (MBP) were assessed in blood samples from 27 multiple sclerosis (MS) patients, 20 patients with other neurologic diseases (OND), and 26 normal subjects, using five MBP preparations with different histories and electrophoretic characteristics to enhance the spectrum of epitopes represented. Substantial variations were observed in the ability of different MBP preparations to induce blood T cell proliferation in a given donor. However, four out of five of the MBPs induced modest but significant proliferation in the MS study population relative to normal individuals, with intermediate responses occurring in OND patients. Positive responses occurred more frequently in MS patients (78%) than in normal donors (31%), and were an important prerequisite for the successful selection of MBP-specific T cell lines.

Cellular and molecular aspects of myelin protein gene expression

The cellular and molecular aspects of myelin protein metabolism have recently been among the most intensively studied in neurobiology. Myelination is a developmentally regulated process involving the coordination of expression of genes encoding both myelin proteins and the enzymes involved in myelin lipid metabolism. In the central nervous system, the oligodendrocyte plasma membrane elaborates prodigious amounts of myelin over a relatively short developmental period. During development, myelin undergoes characteristic biochemical changes, presumably correlated with the morphological changes during its maturation from loosely-whorled bilayers to the thick multilamellar structure typical of the adult membrane. Genes encoding four myelin proteins have been isolated, and each of these specifies families of polypeptide isoforms synthesized from mRNAs derived through alternative splicing of the primary gene transcripts. In most cases, the production of the alternatively spliced transcripts is developmentally regulated, leading to the observed protein compositional changes in myelin. The chromosomal localizations of several of the myelin protein genes have been mapped in mice and humans, and abnormalities in two separate genes appear to be the genetic defects in the murine dysmyelinating mutants, shiverer and jimpy. Insertion of a normal myelin basic protein gene into the shiverer genome appears to correct many of the clinical and cell biological abnormalities associated with the defect. Most of the dysmyelinating mutants, including those in which the genetic defect is established, appear to exhibit pleiotropy with respect to the expression of other myelin genes. Post-translational events also appear to be important in myelin assembly and metabolism. The major myelin proteins are synthesized at different subcellular locations and follow different routes of assembly into the membrane. Prevention of certain post-translational modifications of some myelin proteins can result in the disruption of myelin structure, reminiscent of naturally occurring myelin disorders. Studies on the expression of myelin genes in tissue culture have shown the importance of epigenetic factors (e.g., hormones, growth factors, and cell-cell interactions) in modulating myelin protein gene expression. Thus, myelinogenesis has proven to be very useful system in which to examine cellular and molecular mechanisms regulating the activity of a nervous system-specific process.

Purification and kinetic mechanism of S-adenosylmethionine: myelin basic protein methyltransferase from bovine brain

The enzyme S-adenosylmethionine (AdoMet): myelin basic protein (MBP) methyltransferase was purified 250-fold from bovine brain with an overall yield of 130%, relative to crude supernatant. The purification involves acid-base and (NH4)2SO4 precipitation, chromatography over Sephadex G-100 and DEAE-cellulose, followed by preparative isoelectric focusing. The enzyme has a pI of 5.60 +/- 0.05, and the Mr is estimated to be between 71,000 (from SDS/polyacrylamide-gel electrophoresis) and 74,500 (from gel filtration). The enzyme is stable at 37 degrees C for over 2 h, is stable frozen and does not require metal ions or reductants. The enzyme shows a high specificity for MBP and does not accept polyarginine as a substrate; F1 histone is methylated at 37% of the rate of MBP. Methylation occurs on an arginine residue in a single h.p.l.c.-resolvable peptide from the tryptic cleavage of MBP. Simple saturation kinetics are observed with respect to both substrates, with Km values of 18 microM and 32 microM for MBP and AdoMet respectively. The simplest kinetic mechanism that is consistent with the data requires ordered rapid-equilibrium binding, with AdoMet as the first substrate. The enzyme isolated in this work is different, both physically and kinetically, from the histone-specific arginine methyltransferases described by other workers. A new, simple, assay system for the methylation of MBP is described.

Mechanism of the interaction between myelin basic protein and the myelin membrane; the role of arginine methylation

The addition of solutions of bovine myelin basic protein to suspensions of unilamellar vesicles prepared from whole myelin suspensions results in the rapid equilibrium association of the vesicles into dimers, followed by time-dependent aggregation reactions. Other cationic proteins also induce the dimerization of the vesicles and equilibrium constants for dimer formation are obtained for bovine myelin basic protein, lysozyme, polyhistidine and myelin basic protein from carp, which differs from the bovine protein in that it contains no methylarginine residues. The bovine protein is more efficient at inducing dimer formation than the carp protein by approximately 0.93 kcal/mole; the carp protein is approximately as effective as the other cationic proteins examined. Complete methylation of the bovine MBP by AdoMet:MBP methyltransferase increases the interaction between MBP and the membrane by approximately 0.13 kcal/mole, consistent with the suggestion that a large portion of the free energy difference between the carp and bovine proteins arises from favorable interactions involving the methylarginine residues.

Reduced S-adenosylmethionine:protein-lysine N-methyltransferase activity (protein methylase III) in shiverer mutant mouse brain

Mice with the dysmyelinating mutation shiverer were studied by measuring the activity of two protein methylases and myelin marker enzymes in the brain. It was observed that S-adenosylmethionine:protein-lysine N-methyltransferase (protein methylase III, EC. 2.1.1.43) activity is significantly reduced in phenotypically affected homozygous shiverer (shi/shi) mutant mouse brain compared to the unaffected heterozygous littermate brain. This reduction in enzyme activity is manifested mainly by reduced formation of trimethyllysine during the in vitro methylation of histone. In contrast, myelin marker enzymes such as 2',3'-cyclic nucleotide 3'-phosphohydrolase and 5'-nucleotidase as well as S-adenosyl-methionine:protein-carboxyl O-methyltransferase (protein methylase II, EC. 2.1.1.24) activities were not significantly affected in these strains of mice.

Studies on myelin-basic-protein methylation during mouse brain development

The synthesis and methylation in vivo of myelin basic protein (MBP) during the mouse brain development has been investigated. When mice ranging in age from 13 to 60 days were injected intracerebrally with L-[methyl-3H]methionine, the incorporation of radioactivity into MBP isolated from youngest brain was found to be the highest and declined progressively in mature brains. This pattern of radioactivity incorporation was inversely correlated with the total amount of MBP in the brains, suggesting a higher ratio of MBP methylation to synthesis in younger brain. To differentiate the relative rate of protein synthesis and methylation, animals were given intracerebral injections of a L-[methyl-3H]methionine and L-[35S]methionine mixture and the ratio of 3H/35S (methylation index) was determined. The ratios in the isolated MBP fractions were higher than those of 'acid extracts' and 'breakthrough' fractions, with a maximal ratio in the youngest brain. This high ratio was well correlated with the higher protein methylase I (PMI) activity in younger brains. The MBP fractions were further separated on SDS/polyacrylamide-gel electrophoresis into several species with apparent Mr ranging from 32,400 to 14,500. The results indicated that each protein species accumulated at a characteristic rate as a function of age. The high-Mr (32,400) species was predominant in younger brain, whereas the smaller MBP was the major species in older brain tissue. The importance of this developmental pattern of MBP synthesis and methylation is discussed in relation to PMI activity.

Myelin basic protein inhibits histone-specific protein methylase I

Bovine brain myelin basic protein, free of associated proteolytic activity, was found to be a specific inhibitor of histone-specific protein methylase I (S-adenosyl-L-methionine:protein-L-arginine N-methyltransferase, EC 2.1.1.23) purified from bovine brain. 50% of the methyl group incorporation into the histone substrate catalyzed by the methylase I was inhibited by myelin basic protein at a concentration of 0.326 mM. However, neither of the peptide fragments (residues 1-116 and residues 117-170) generated by the chemical cleavage of myelin basic protein at the tryptophan residue retained the inhibitory activity for histone-specific protein methylase I. Proteins such as gamma-globulin, bovine serum albumin, bovine pancreatic ribonuclease and polyarginine did not exhibit significant inhibitory activity toward the enzyme. The Ki value for myelin basic protein was estimated to be 3.42 X 10(-5) M for histone-specific protein methylase I and the nature of the inhibition was uncompetitive toward histone substrate.

A new form of myelin basic protein found in human brain

Human myelin basic protein was subjected to ion-exchange chromatography at high pH to separate the differently charged components. Polyacrylamide gel electrophoretic patterns of the fractions showed that the less basic fractions 3, 4, and 5 contained significant amounts of a protein somewhat smaller than the more common 18.5-kDa form. Fraction 3 consisted of approximately equal amounts of this smaller polypeptide and component 3, the 18.5-kDa form found in other mammalian myelin basic protein preparations. The two proteins in fraction 3 were separated by fast protein liquid chromatography. Both have blocked N termini and identical C termini (-Met-Ala-Arg-Arg). When the tryptic digests of the two proteins were fractionated by HPLC, the elution profiles were similar, except that four peaks found in the chromatogram of the larger protein were missing from the chromatogram of the smaller one. In addition, an extra peak was found in the elution pattern of the latter chromatogram. Amino acid analysis of the individual tryptic peptides indicated that the smaller protein lacked residues 106-116 (-Gly-Arg-Gly-Leu-Ser-Leu-Ser-Arg-Phe-Ser-Trp-). The deleted portion corresponds exactly to the amino acid sequence encoded by exon 5 of the mouse basic protein gene. This new form of myelin basic protein has a molecular weight of 17,200, calculated from its amino acid composition.

Neurotoxicity in long-term survivors of small cell lung cancer

Chronic central nervous system neurotoxicity was studied in 38 long-term survivors (greater than or equal to 3 years) of small cell lung cancer who were treated at the University of Texas M. D. Anderson Hospital and Tumor Institute at Houston between 1971 and 1980. All but one patient received combination chemotherapy with or without chest irradiation. Twenty-four patients received whole brain irradiation (Group I), 22 for "elective" and two for therapeutic purposes, while 14 did not (Group II). Abnormalities in computed tomographic (CT) scans of the brain were more frequently observed in Group I than in Group II (70% vs. 0%, p less than 0.01). Clinical central nervous system neurotoxicity developed in three patients in Group I, while none developed in patients in Group II (p less than 0.05). Patients who received methotrexate and procarbazine after whole brain irradiation were at a higher risk for clinical central nervous system neurotoxicity (p less than 0.05), and for development of periventricular white matter changes in CT brain scans (p less than 0.05) than were patients in Group II. Impaired methylation of the myelin sheath is proposed as a possible underlying pathogenic mechanism.

Correlation between inhibition of myelin basic protein (arginine) methyltransferase by sinefungin and lack of compact myelin formation in cultures of cerebral cells from embryonic mice

Sinefungin, a known inhibitor of protein methylation, inhibited the myelin basic protein (arginine) methyltransferase activity in homogenates of cultured cerebral cells from embryonic mice. Fifty percent inhibition was achieved with 25 microM sinefungin. Electron microscopic examination of the myelin fraction, isolated by gradient density centrifugation and obtained from untreated cells, revealed numerous ringlike multilamellar membranous substructures that had a major dense line periodicity, compactness, and the general appearance expected of myelin obtained by the same technique from whole brain. Cells treated with 30 microM sinefungin, which inhibits myelin basic protein methyltransferase in broken cell preparations about 60%, produced ringlike structures that were devoid of multilamellar periodicity and compactness reminiscent of the vacuolated myelin observed in subacute combined degeneration and in nitrous-oxide- or cycloleucine-treated animals in which methyltransferase activity is also inhibited. The sinefungin-induced change in multilamellar periodicity cannot be attributed to a lack of myelin basic protein, since the ratio of myelin basic protein to total protein did not decrease in sinefungin-treated cells. This primary culture system should be useful for further evaluating the hypothesis that the methylation of myelin basic protein is related to the formation of compact myelin.

Aliphatic aldehydes promote myelin basic protein-induced fusion of phospholipid vesicles

Myelin basic protein induces slow and limited fusion of phospholipid vesicles composed of a mixture of phosphatidylcholine and phosphatidylethanolamine. Addition of palmitoyl aldehyde to these vesicles dramatically increases their ability to fuse in the presence of myelin basic protein. Compared to aliphatic aldehydes, fatty acids are much less potent promoters of myelin basic protein-induced membrane fusion. The ability of aliphatic aldehydes to promote myelin basic protein-induced membrane fusion may be of relevance to myelin structure and function and, particularly, to the pathology of demyelinating diseases such as multiple sclerosis.

Clustering of glycine and NG,NG-dimethylarginine in nucleolar protein C23

Protein C23 (Mr 110 000, pI = 5.5), a major phosphoprotein in the nucleolus of mammalian cells, has been shown to contain 1.3 mol% of NG,NG-dimethylarginine (DMA) [Lischwe, M.A., Roberts, K.D., Yeoman, L.C., & Busch, H. (1982) J. Biol. Chem. 257, 14600-14602]. A tryptic peptide from protein C23 that contains DMA has been isolated and sequenced. Its sequence is Gly-Glu-Gly-Gly-Phe-Gly-Gly-DMA-Gly-Gly-Gly-DMA-Gly-Gly-Phe-Gly-Gly-DMA- Gly-Gly- Gly-DMA-Gly-Gly-DMA-Gly-Gly-Phe-Gly-Gly-DMA-Gly-DMA-Gly-Gly-Phe-Gly-Gly- DMA-Gly-Gly-Phe-DMA-Gly-Gly-DMA-Gly-Gly-Gly-Gly-Asp-Phe-Lys. This peptide contains 34 glycine, 10 DMA, and 6 phenylalanine residues and has clusters of glycine and NG,NG-dimethylarginine interspersed with phenylalanine residues. A similar domain has been found at the amino terminus of a nucleolar protein of Mr 34,000, pI = 8.5. This sequence array may represent a conserved domain characteristic of a certain class of nuclear proteins. All of the methylated arginine residues in protein C23, the 34-kilodalton protein, and myelin basic protein [Carnegie, P.R. (1971) Biochem. J. 123, 57-67] have at least one adjacent glycine. Access of certain arginine methylases to arginine residues may be sterically possible because of the lack of a side chain on the adjacent glycine residue(s).

Disorders of cobalamin metabolism

Recent developments in our knowledge of the biochemistry and metabolism of cobalamin have given us some insight into clinical disorders. N2O, which easily induces cobalamin deficiency, both in vivo and in vitro, has greatly contributed to the investigation of the cobalamin deficient state, especially in relation to folate and amino acid metabolism. Demonstration of the cobalamin analog in human serum and a new enzyme which requires cobalamin as a coenzyme has led to recent increased interest in this field. The disorders of cobalamin metabolism will be summarized briefly as well as those areas currently of particular interest.

Studies on myelin basic protein-specific protein methylase I in various dysmyelinating mutant mice

Jimpy mice are dysmyelinating mutants characterized by producing near normal levels of myelin basic protein (MBP) in the brain but failing to incorporate these proteins into the myelin sheath. In this study, the activity of MBP-specific protein-arginine N-methyltransferase (protein methylase I) was studied in the brains of normal and jimpy mice of different ages. The enzyme activity varied little with age in normal mice but in 18 and 21 days-old homozygous jimpy mice the activity was reduced by 50% and 75% respectively from the level of their normal littermates. Interestingly, however, heterozygous jimpy mice who are phenotypically normal and quaking mice (a similar dysmyelinating mutant) showed unaltered enzyme levels.

Regulation of myelin basic protein (arginine) methyltransferase by thyroid hormone in myelinogenic cultures of cells dissociated from embryonic mouse brain

The ontogenetic expression of myelin basic protein (arginine) methyltransferase in myelinogenic cultures of cells dissociated from embryonic mouse brain is highly dependent on the presence of thyroid hormone. Restoration of myelin basic protein methyltransferase to normal activities occurred 16 h after the addition of 100 nM L-3,5,3'-triiodothyronine to hypothyroid medium. These data demonstrate that thyroid hormone can regulate a posttranslational event. On the other hand, histone (arginine) methyltransferase has a different temporal activity pattern, which is not coordinated with myelination, and is not influenced by the lack of thyroid hormone. These data, which suggest the existence of two methyltransferases, were substantiated by demonstrating that the total amount of methylation of added myelin basic protein and histone is the same whether they are incubated together or separately. The requirement of thyroid hormone for the expression of the myelin basic protein methyltransferase and not for histone methyltransferase suggests that thyroid hormone preferentially regulates myelin-associated events in these cultures.

Phosphate groups modifying myelin basic proteins are metabolically labile; methyl groups are stable

Young and adult rats received intracranial injections of [33P]orthophosphoric acid. The time course of the appearance and decay of the radioactive label on basic proteins in isolated myelin was followed for 1 mo. Incorporation was maximal by 1 h, followed by a decay phase with a half-life of approximately 2 wk. However, radioactivity in the acid-soluble precursor pool (which always constituted at least half of the total radioactivity) decayed with a similar half-life, suggesting that the true turnover time of basic protein phosphates might be masked by continued exchange with a long-lived radioactive precursor pool. Calculations based on the rate of incorporation were made to more closely determine the true turnover time; it was found that most of the phosphate groups of basic protein turned over in a matter of minutes. Incorporation was independent of the rate of myelin synthesis but was proportional to the amount of myelin present. Experiments in which myelin was subfractionated to yield fractions differing in degree of compaction suggested that even the basic protein phosphate groups of primarily compacted myelin participated in this rapid exchange. Similar studies were carried out on the metabolism of radioactive amino acids incorporated into the peptide backbone of myelin basic proteins. The metabolism of the methyl groups of methylarginines also was monitored using [methyl-3H]methionine as a precursor. In contrast to the basic protein phosphate groups, both the peptide backbone and the modifying methyl groups had a metabolic half-life of months, which cannot be accounted for by reutilization from a pool of soluble precursor. The demonstration that the phosphate groups of myelin basic protein turn over rapidly suggests that, in contrast to the static morphological picture, basic proteins may be readily accessible to cytoplasm in vivo.

Cobalamin inactivation by nitrous oxide produces severe neurological impairment in fruit bats : protection by methionine and aggravation by folates

Nitrous oxide, which inactivates cobalamin when administered to fruit bats, results in severe neurological impairment leading to ataxia, paralysis and death. This occurs after about 6 weeks in animals depleted of cobalamin by dietary restriction, and after about 10 weeks in cobalamin replete bats. Supplementation of the diet with pteroylglutamic acid caused acceleration of the neurological impairment - the first unequivocal demonstration of aggravation of the neurological lesion in cobalamin deficiency by pteroylglutamic acid. The administration of formyltetrahydropteroylglutamic acid produced similar aggravation of the neurological lesion. Supplementation of the diet with methionine protected the bats from neurological impairment, but failed to prevent death. Methionine supplementation protected against the exacerbating effect of folate, preventing the development of neurological changes. These findings lend support to the hypothesis that the neurological lesion in cobalamin deficiency may be related to a deficiency in the methyl donor S-adenosylmethionine which follows diminished synthesis of methionine.

The relationship of myelin basic protein (arginine) methyltransferase to myelination in mouse spinal cord

The relationship between the activity of myelin basic protein (arginine) methyltransferase and myelination in the mouse spinal cord has been examined. The activity of this methylase increases between 8 and 45 days postnatal age and correlates well with other parameters of myelination. A comparison of myelin basic protein methylase with histone methylase activity during development indicates that each is a distinct, specific enzyme activity. Together, these results are considered to establish myelin based protein methylase as a myelination-related enzyme.

In vivo methylation of an arginine in chicken myelin basic protein

The amino acid sequence around the sole methylarginine residue in chicken myelin basic protein was determined and was found to be similar to that previously reported for mammalian myelin basic protein. The ratio NG, N'G-dimethylarginine: NG-monomethylarginine:arginine was approximately 1.3:0.9:1.0. No NG, NG-dimethylarginine was detected in the protein. The in vivo incorporation of methyl groups from [methyl-3H]methionine into methylarginines in myelin was found to occur readily in 2-day-old chickens. Radioactively labelled NG,N'G-dimethylarginine and NG-monomethylarginine in myelin were derived solely from myelin basic protein. Radioactivity was also incorporated into NG,NG-dimethylargnine, although this was not derived from myelin basic protein. As NG-monomethylarginine was easily separated from the dimethylarginines, and as it was derived from myelin basic protein, it may be a good marker for myelin basic protein turnover in vivo. A time course study of the incorporation showed that radioactivity was incorporated into NG-monomethylarginine up to 6 h after injection, and decayed slowly, with an apparent half-life of about 40 days.

Tobacco-alcohol amblyopia: a proposed biochemical basis for pathogenesis

Tobacco-alcohol or nutritional amblyopia is a rare disorder of decreased central vision associated with nutritional deficiencies and tobacco smoking. although folate deficiency is common in patients with tobacco-alcohol amblyopia, the role of folic acid in this disorder has been underplayed. The role of cyanide from tobacco smoke, folate and other dietary deficiencies will be reviewed. A new model of the pathogenesis of tobacco-alcohol amblyopia is proposed based on the presumptive alteration of methionine and S-adenosyl-L-methionine metabolism.

Cycloleucine-induced vacuolation of myelin is associated with inhibition of protein methylation

Chickens injected with cycloleucine developed vacuolation of myelin similar to that seen in humans with vitamin B12 deficiency. Cycloleucine, an inhibitor of the formation of S-adenosylmethionine, decreased the incorporation of methyl groups into methylarginine in myelin basic protein in vivo. The need for methylcobalamin for the conversion of homocysteine to methionine and the requirement that myelin basic protein may be methylated, offer a rational explanation for the myelin lesions observed in cases of vitamin B12 deficiency where there is increasing evidence that methyl-, rather than adenosylcobalamin is required to prevent dysmyelination.

Posttranslational covalent modification of proteins

A search for derivatized amino acids in proteins has shown that the extent of posttranslational modification of proteins is quite substantial. While only 20 primary amino acids are specified in the genetic code and are involved as monomer building blocks in the assembly of the polypeptide chain, about 140 amino acids and amino acid derivatives have been identified as constituents of different proteins in different organisms. A brief consideration of the questions about where and when the derivatization reactions occur, how the specificity of the reactions is established, and how the posttranslational modifications can facilitate biological processes, reveal a need for more information on all these points. Answers to these questions should represent significant contributions to our understanding of biochemistry and cell biology.

Autoimmune disease antigens

The first step towards understanding the cellular interaction which results in autoimmune disease is to determine what triggers the recognition between a specific autoimmune antigen determinant and the cellular receptor. In this review, we have focused on the antigen inducing experimental allergic encephalitis (EAE) because the antigen has been characterized and a relatively large body of information on its biological activities has been accumulated. Clearly, a specific allergic encephalitis-producing determinant is present and is represented on a relatively small portion of the molecule. The determinant induces a wide variety of biological reactivities, some of which are classed as cellular mediated. An attempt is made to dissect activities such as blast transformation (BT), migration inhibitory factor (MIF), in vivo delayed type hypersensitivity reaction (DTH) and EAE and to relate them to the structural requirements which the determinants possess. The complexities which arise indicate that subpopulations of cells with different receptor activities may respond selectively and that recognition of the receptor is produced by an EAE determinant consisting of three amino acids in a specific linear sequence. Furthermore, under experimental circumstances the EAE activity can be dissociated from the other activities (BT, MIF, DTH), indicating that while these tests are used generally to follow various human autoimmune disease activities, they may represent the reaction of a broad spectrum of cells.

Urinary excretion of methylarginine in human disease

Methylated amino acids are excreted in urine upon degradation of some tissue proteins. The urinary excretion ratios of NG,N'G-dimethylarginine (syn-DMA) and NG,NG-dimethylarginine (unsym-DMA) were studied in healthy adults and in patients with various diseases. The normal ratio of sym- to unsym-DMA in urine was 0.98 and ranged from 0.71 to 1.33; ratios were not significantly different in multiple sclerosis, cerebrovascular accident, cancer, and systemic lupus erythematosus. However, patients with liver, disease, including chronic active hepatitis, were found on average to have a significantly altered ratio of 0.79, range 0.49-1.30, owing to an increase in the excretion of unsym-DMA. Hence measurements of the urinary excretion of dimethylarginine could become a useful aid in assessing recovery of liver cells in patients with chronic liver disease.

S-adenosylmethionine: protein-arginine methyltransferase. Purification and mechanism of the enzyme

Protein methylase I (S-adenosylmethionine: protein-arginine methyltransferase, EC 2.1.1.23) has been purified from calf brain approximately 120-fold with a 14% yield. The final preparation is completely free of any other protein-specific methyltransferases and endogenous substrate protein. The enzyme has an optimum pH of 7.2 and pI value of 5.1. The Km values for S-adenosyl-L-methionine, histone H4, and an ancephalitogenic basic protein are 7.6 X 10(-6), 2.5 X 10(-5), and 7.1 X 10(-5) M, respectively, and the Ki value for S-adenosyl-L-homocysteine is 2.62 X 10(-6) M. The enzyme is highly specific for the arginine residues of protein, and the end products after hydrolysis of the methylated protein are NG,NG-di(asymmetric), NG,N'G-di(symmetric), and NG-monomethylarginine. The ratio of [14C]methyl incorporation into these derivatives by enzyme preparation at varying stages of purification remains unchanged at 40:5:55, strongly indicating that a single enzyme is involved in the synthesis of the three arginine derivatives. The kinetic mechanism of the protein methylase I reaction was studied with the purified enzyme. Initial velocity patterns converging at a point on the extended axis of abscissas were obtained with either histone H4 or S-adenosyl-L-methionine as the varied substrate. Product inhibition by S-adenosyl-L-homocysteine with S-adenosyl-L-methionine as the varied substrate was competitive regardless of whether or not the enzyme was saturated with histone H4. On the other hand, when histone H4 is the variable substrate, noncompetitive inhibition was obtained with S-adenosyl-L-homocysteine under conditions where the enzyme is not saturated with the other substrate, S-adenosyl-L-methionine. These results suggest that the mechanism of the protein methylase I reaction is a Sequential Ordered Bi Bi mechanism with S-adenosyl-L-methionine as the first substrate, histone H4 as the second substrate, methylated histone H4 as the first product, and S-adenosyl-L-homocysteine as the second product released.

Studies on the catabolism of Ng-methylarginine, Ng, Ng-dimethylarginine and Ng, Ng-dimethylarginine in the rabbit

1. The routes of elimination of Ng-methylarginine, Ng, Ng-dimethylarginine and Ng, Ng-dimethylarginine were investigated in the rabbit. 2. Analyses showed low plasma concentrations of these amino acids (around 1 nmol/ml) and ratios similar to those found in tissue proteins. The concentrations of these amino acids in extracts of brain, kidney, liver and spleen were similar except that liver had a lower concentration of Ng-methylarginine and Ng, Ng-dimethylarginine. Cerebrospinal fluid contained traces of each amino acid.

Amino acid sequence of the smaller basic protein from rat brain myelin

1. The complete amino acid sequence of the smaller basic protein from rat brain myelin was determined. This protein differs from myelin basic proteins of other species in having a deletion of a polypeptide of 40 amino acid residues from the centre of the molecule. 2. A detailed comparison is made of the constant and variable regions in a group of myelin basic proteins from six species. 3. An arginine residue in the rat protein was found to be partially methylated. The ratio of methylated to unmethylated arginine at this position differed from that found for the human basic protein. 4. Three tryptic peptides were isolated in more than one form. The differences between the two forms of each peptide are discussed in relation to the electrophoretic heterogeneity of myelin basic proteins, which is known to occur at alkaline pH values. 5. Detailed evidence for the amino acid sequence of the protein has been deposited as Supplementary Publication SUP 50029 at the British Library (Lending Division) (formerly the National Lending Library for Science and Technology), Boston Spa, Yorks. LS23 7BQ, U.K., from whom copies may be obtained on the terms given in Biochem. J. (1973) 131, 5.

Myelin basic protein: location of multiple independent antigenic regions

Immnunization of guinea pigs with homologous myelin basic protein induces antibodies that differ in their ability to bind specific peptide fragments of the protein. Antiserums with differing specificities made it possible to demonstrate at least three mutually exclusive antigenic sites in the protein molecule. One of these sites is located between residues 44 and 89, another between 90 and 116, and the third between 117 and 170.

Phosphorylation of myelin basic protein by an adenosine 3':5'-cyclic monophosphate-dependent protein kinase

Myelin basic protein was shown to be a substrate for protein kinase from rabbit muscle. One of the major sites of phosphorylation was the serine residue in the sequence Gly-Arg-Gly-Leu-Ser-Leu. The arginine residue in this sequence is known to be a substrate for a protein methylase.