Enhancement of HIV-1-induced syncytium formation in T cells by the tyrosyl kinase p56lck

The CD4 glycoprotein is the primary cellular receptor for human immunodeficiency virus type 1 (HIV-1) and has also been reported to be physically associated with p56lck, a tyrosyl protein kinase p56lck is a member of the src family of nonreceptor protein-tyrosine kinases and is expressed predominantly in T lymphocytes. Our objective was to study the effect of p56lck on the biology of HIV-1. For this purpose, we have stably transfected two human p56lck negative T cell lines (C8166-45 and MT-2) with plasmids encoding for this cellular protein. Following coculture with HIV-1-infected cells or infection with cell-free virus, p56lck-expressing cell lines showed a greater propensity for virus-mediated syncytium formation than parental p56lck-negative cells. The enhancement of HIV-1-induced syncytium formation was not associated with the kinase activity of p56lck, as demonstrated by experiments using a kinase-deficient mutant. However, the physical interaction between CD4 and p56lck was shown to be necessary to obtain the enhancement of syncytium formation since a mutated version of p56lck, which is deficient in its capacity to associate with CD4, did not lead to an increase in virus-mediated cell-to-cell fusion events. Finally, we determined that cells transfected with wild-type and kinase-negative mutant p56lck showed a reduced rate of CD4 endocytosis compared to parental p56lck-negative cells. Together, these results suggest that p56lck can be seen as an accessory molecule facilitating HIV-1-mediated syncytium formation in T cells by a mechanism involving the stabilization of the CD4 molecule at the cell surface.

Characterization of metal and nucleotide liganded forms of adenylate kinase by electrospray ionization mass spectrometry

Complexes of adenylate kinase from Escherichia coli, Bacillus subtilis, and Bacillus stearothermophilus with the bisubstrate nucleotide analog P1,P5-di(adenosine 5')-pentaphosphate and with metal ions (Zn2+ and/or Mg2+) were analyzed by electrospray ionization mass spectrometry. P1,P5-di(adenosine 5')-pentaphosphate. adenylate kinase complex was detected in the positive mode at pH as low as 3.8. Binding of nucleotide to adenylate kinase stabilizes the overall structure of the protein and preserves the Zn2+ chelated form of the enzyme from the gram-positive organisms. In this way, it is possible in a single mass spectrometry experiment to screen metal-chelating adenylate kinases, without use of radioactively labeled compounds. Binding of Mg2+ to enzyme via P1,P5-di(adenosine 5')-pentaphosphate was also demonstrated by mass spectrometry. Although no amino acid side chain in adenylate kinase is supposed to interact with Mg2+, Asp93 in porcine muscle cytosolic enzyme, equivalent to Asp84 in the E. coli adenylate kinase, was proposed to stabilize the nucleotide.Mg2+ complex via water molecules.

Binding of HIV-1 to its receptor induces tyrosine phosphorylation of several CD4-associated proteins, including the phosphatidylinositol 3-kinase

Cell surface CD4 molecules are known to be important in several physiological responses of T lymphocytes. The use of human immunodeficiency virus (HIV) particles or purified gp120 molecules as CD4 cross-linking agents has been shown to result in a cascade of intracellular biochemical events. In addition, we and other have provided evidence suggesting that virus-mediated CD4 multimerization can lead to modulation of HIV-1 long terminal repeat-dependent activity and virus production. We were thus interested in measuring the effect of HIV-1 particles on intracellular tyrosine-phosphorylation levels, mostly of CD4-associated proteins. Using the T cell line CEM-T4, we observed that HIV-1 induces an increase in tyrosine phosphorylation of four major proteins physically complexed to the CD4 molecule. Immunoblot analysis permitted the identification of two of these proteins, p56lck and phosphatidylinositol 3-kinase (PI 3-kinase) p85 alpha. No concomitant variation in the level of these two CD4-associated proteins was observed after HIV-1-induced CD4 cross-linking. To our knowledge, this is the first report linking HIV-1-mediated CD4 multimerization to an increase in tyrosine phosphorylation of the PI 3-kinase complex. The four CD4-associated molecules described in this report are most likely implicated in virus-induced CD4-linked signaling events.

Metabolic studies in twin brothers with 2-methylacetoacetyl-CoA thiolase deficiency

We report clinical and biological investigations in two patients (twin brothers) with 2-methylacetoacetyl-CoA thiolase deficiency. Main clinical features included important staturo-ponderal delay, frequent infectious rhinopharyngitis episodes and an acute metabolic acidosis at the age of 4 years, this metabolic decompensation being adequately halted by bicarbonate supplementation. Since that age, patients developed rather favorably, however, with persistence of the staturo-ponderal delay. Organicaciduria typical of 2-methylacetoacetyl-CoA thiolase deficiency was recorded consisting of excessive excretion of tiglylglycine, 2-methyl-3-hydroxybutyrate, 3-hydroxyisovalerate, 2-methylglutaconate, adipate and 2-methylacetoacetate. Blood carnitine levels were altered in patients with increased total and esterified carnitine concentrations and enhanced acyl/free carnitine ratios. Determination of acylcarnitine profiles showed that patients excreted excessive amounts of several acylcarnitines in urine including propionyl, butyryl, isobutyryl, isovaleryl, 2-methylbutyryl and tiglyl-carnitine, the latter acylcarnitine being prominent with, in one of the patients, occurrence of a previously undescribed isomer of this carnitine ester, possibly 2-ethylacrylyl-carnitine. Excretion of these acylcarnitines in urine was increased in response to L-carnitine although, as a whole, this therapy resulted in a less important stimulation of esterified carnitine removal in urine from patients than in the case of supplemented controls. Biochemical investigations on cultured skin fibroblasts confirmed 2-methylacetoacetyl-CoA thiolase deficiency. Through the present report on this rare disease in two siblings, we would like to underline that acylcarnitines can be used in the diagnosis of 2-methylacetoacetyl-CoA thiolase deficiency, a view supported by acylcarnitine profiles further determined in another patient with proven oxothiolase deficiency, adding this pathology to the list of beta-oxidation disorders that may be screened successfully through determination of acylcarnitine profiles in body fluids.

Acylcarnitine removal in a patient with acyl-CoA beta-oxidation deficiency disorder: effect of L-carnitine therapy and starvation

Carnitine levels and acylcarnitine profiles in a patient with mild multiple acyl-CoA dehydrogenase deficient beta-oxidation were compared with control results. Whereas blood and urine total carnitine levels were moderately decreased, blood esterified carnitine levels in the patient were about 2-fold higher than in controls. Urinary acylcarnitine profiles presented with a larger variety of carnitine esters than in controls and included propionylcarnitine, butyrylcarnitine, 2-methylbutyrylcarnitine, hexanoylcarnitine and octanolycarnitine. Total carnitine levels in body fluids were similarly affected by chronic oral L-carnitine administration in patient and controls. By contrast, esterified carnitine level increase was 2-fold more important in controls than in patient. Whereas no qualitative changes in urinary acylcarnitine profiles were induced by L-carnitine therapy in controls, several alterations of these profiles were observed in the patient. The effect of starvation on metabolites was also studied, especially beta-oxidation rates assessed by free fatty acids to 3-hydroxybutyric acid ratios in blood from the patient in the untreated and L-carnitine treated states. In the L-carnitine-supplemented patient, the effect of starvation on the time course of carnitine levels and acylcarnitine profiles could also be documented. The ability of chronic oral L-carnitine administration to remove relatively less important amounts of acylcarnitines in the patient than in controls is further discussed, as well as qualitative alterations of acylcarnitine profiles induced by this therapy in the pathological condition.

CMP kinase from Escherichia coli is structurally related to other nucleoside monophosphate kinases

CMP kinase from Escherichia coli is a monomeric protein of 225 amino acid residues. The protein exhibits little overall sequence similarities with other known NMP kinases. However, residues involved in binding of substrates and/or in catalysis were found conserved, and sequence comparison suggested conservation of the global fold found in adenylate kinases or in several CMP/UMP kinases. The enzyme was purified to homogeneity, crystallized, and analyzed for its structural and catalytic properties. The crystals belong to the hexagonal space group P6(3), have unit cell parameters a = b = 82.3 A and c = 60.7 A, and diffract x-rays to a 1.9 A resolution. The bacterial enzyme exhibits a fluorescence emission spectrum with maximum at 328 nm upon excitation at 295 nm, which suggests that the single tryptophan residue (Trp30) is located in a hydrophobic environment. Substrate specificity studies showed that CMP kinase from E. coli is active with ATP, dATP, or GTP as donors and with CMP, dCMP, and arabinofuranosyl-CMP as acceptors. This is in contrast with CMP/UMP kinase from Dictyostelium discoideum, an enzyme active on CMP or UMP but much less active on the corresponding deoxynucleotides. Binding of CMP enhanced the affinity of E. coli CMP kinase for ATP or ADP, a particularity never described in this family of proteins that might explain inhibition of enzyme activity by excess of nucleoside monophosphate.

Analysis by electrospray mass spectrometry of glycopeptides from the in vitro O-glycosylation reaction using human mucin motif peptide

A mucin-motif peptide in the one-letter code T T T P S P P M T T P I T P P A, representative of the human intestinal mucin tandem repeat sequence (MUC2), containing several threonine residues in clusters, was used as an acceptor substrate to investigate the effect of peptide structure on the activity of crude preparation of human gastric UDP-GalNAc:polypeptide N-acetyl galactosaminyltransferases. High-performance liquid chromatography was performed to separate the different products of the in vitro O-glycosylated reaction. The electrospray mass spectrometry was used to identify the different masses (m/z) of these products. Although the m/z of glycopeptide(s) could be higher than the detection limits of the spectrometer, an accurate study of the doubly charged ions allowed us to demonstrate the linkage of more than two sugars. Hence, the peptide MUC2 will accept at least four carbohydrate residues but the exact substituted positions should be confirmed by further sequence determination.

Vitamin A and E blood levels in erythrodermic and pustular psoriasis associated with chronic alcoholism

Vitamin A and E blood levels were determined, using a high-performance liquid chromatographic method, in 7 patients with erythrodermic psoriasis or psoriatic acral pustulosis associated or not associated with chronic alcoholism, during and after the acute episode. These vitamins were also studied in 5 patients with psoriasis vulgaris involving more than 80% of the surface body area and associated with chronic alcohol intake and in 17 patients with psoriasis vulgaris involving more than 50% of the skin but without chronic alcoholism. Vitamin A blood levels were reduced in all the patients in the group "erythrodermic psoriasis/psoriatic acral pustulosis", while vitamin E blood levels were below the normal range during the acute psoriatic episode only in the 5 patients having a history of chronic alcohol intake in this group. In the other groups--psoriasis vulgaris with chronic alcoholism and psoriasis vulgaris without heavy alcohol consumption--vitamin A and E blood levels were not reduced. The implication of vitamin E in psoriasis, probably by its antioxidant activity, and its relationship with selenium are discussed. We suggest that attention should be paid to the vitamin A deficiency in erythrodermic or pustular psoriasis and to the vitamin E deficiency when these inflammatory diseases are associated with chronic alcoholism.

Application of electrospray and fast atom bombardment mass spectrometry to the identification of post-translational and other chemical modifications of proteins and peptides

Mass spectrometry is a very powerful tool in the identification of chemical modifications of proteins and peptides. Often these modifications cannot be determined by conventional techniques. This report describes the combined use of electrospray ionization mass spectrometry and fast atom bombardment mass spectrometry to complete the primary structure of proteins and peptides. Examples illustrate how mass spectrometry is used to locate sites of phosphorylation, methylation and acetylation, and identify blocking groups and unexpected side reactions such as deamidation or alkylation.

A corrected primary structure for dog-fish Scylliorhinus caniculus protamine Z3

We have redetermined the primary structure for dog-fish protamine using automated amino-acid sequencing associated to mass spectrometry techniques and report, on the basis of these findings, that the previously published amino-acid sequence is incorrect. The correct protamine sequence is 37 amino acids long and differs from the original published sequence by the C-terminal hexapeptide Arg32-Gly-Arg-Arg-Ser-Arg37.

Variation in 8-methoxypsoralen profiles during long-term psoralen plus ultraviolet A therapy and correlations between serum 8-methoxypsoralen levels and chromametric parameters

Three serum 8-methoxypsoralen (8-MOP) kinetics tests were performed on 15 patients undergoing PUVA therapy. The first test was carried out before beginning PUVA treatment, the 2nd one at the 10th session and the 3rd test at the 20th PUVA session. Blood samples were taken every 30 min after the drug was taken and a standard meal ingestion during 3 h to determine the serum 8-MOP peak level and corresponding time. For 14 patients, UVA-induced erythema was measured with a Minolta CR 200 chromameter, 3 (before beginning PUVA treatment, just before 10th session and 48 h later) or 5 times (before beginning PUVA treatment, just before 10th session and 48 h later, just before 20th session and 48 h later). There was a wider distribution of serum 8-MOP peak levels in the 3rd test than in 2nd one and in the 2nd one than in the first one. These facts suggest a heterogeneity in 8-MOP metabolism in the 15 patients: 11 patients showed an earlier serum 8-MOP peak and an earlier appearance of the drug in blood in the 3rd and 2nd test than in the first one. For 9 of these 11 patients, serum 8-MOP peak levels were higher and higher from the first profile to the 3rd one, suggesting an inhibition of 8-MOP metabolism in time. In the remaining 4 patients, the 8-MOP peak time and the appearance of the drug in blood were delayed in the 3rd test compared with the first profile.(ABSTRACT TRUNCATED AT 250 WORDS)

Nuclear transition protein 1 from ram elongating spermatids. Mass spectrometric characterization, primary structure and phosphorylation sites of two variants

The ram transition protein 1 (TP1) is present in spermatid cell nuclei in the nonphosphorylated, monophosphorylated and diphosphorylated forms. Its primary structure was determined by automated Edman degradation of S-carboxamidomethylated protein and of peptides generated by cleavage with thermolysin and endoproteinase Lys-C. The ram TP1 is a small basic protein of 54 residues and structurally very close to other mammalian TP1. The mass spectrometric data obtained from the protein and its fragments reveal that ram TP1 is indeed a mixture (approximately 5:1) of two structural variants (Mr 6346 and 6300). These variants differ only by the nature of the residue at position 27 (Cys in the major variant and Gly in the minor variant). The study of phosphorylation sites has shown that four different serine residues could be phosphorylated in the monophosphorylated TP1, at positions 8, 35, 36 or 39. From previous physical studies, it has been postulated that the Tyr32 surrounded by two highly conserved basic clusters was responsible for the destabilization of chromatin by intercalation of its phenol ring between the bases of double-stranded DNA. The presence of three phosphorylatable serine residues in the very conserved sequence 29-42 is another argument for the involvement of this region in the interaction with DNA.

Cuttlefish sperm protamines. 2. Mass spectrometry of protamines and related peptides

The sequence of very basic proteins such as protamines (more than 50% arginines) and related peptides has been determined using mass spectrometry in conjunction with Edman degradation. The capabilities of three mass spectrometric (MS) techniques [fast-atom-bombardment (FAB), 252Cf plasma desorption (252CFPD) and electrospray (ES)] have been evaluated on stallion protamine 1, cuttlefish protamine, and the corresponding cleavage peptides. In contrast to FAB-MS and 252Cf PD-MS, ES-MS made possible an easy determination of the molecular mass of the intact protamines (approximately 8 kDa). With ES-MS about 0.2 nmol was sufficient to yield a mass measurement with an accuracy of 0.05%. On peptides smaller than 3500 Da, both FAB-MS and 252Cf PD-MS allowed mass measurements with an accuracy of 0.1%. 252Cf PD-MS appeared more sensitive than FAB-MS by about a factor of 10. FAB-MS is nevertheless particularly interesting since in most cases it produced spectra with intense A-type fragmentation ions which provided reliable primary structure information.

Nuclear basic protein transition during sperm differentiation. Primary structure of the spermatid-specific protein S2 from the dog-fish Scylliorhinus caniculus

The remodeling of nucleoproteins during dog-fish spermiogenesis involves two successive nuclear protein transitions: the first from somatic-type histones to transition proteins during the nuclear elongation of spermatids and the second leading to protamine-DNA association in mature spermatozoa. The chromatin of elongating spermatids contains two transition proteins called S1 and S2. The amino acid sequence of protein S1, a polypeptide of 87 residues was determined previously [Chauvière, M., Martinage, A., Briand, G., Sautière, P. & Chevaillier, Ph. (1987) Eur. J. Biochem. 169, 105-111]. In the present paper, we report the elucidation of the primary structure of the minor transition protein S2 established by automated Edman degradation of the protein and of its fragments generated by cleavage at methionine and aspartate residues. S2 contains 80 residues and has a molecular mass of 9726 Da. S2 is mainly characterized by a high content of basic amino acids mostly represented by lysine, a relatively high level of hydrophobic residues, the presence of six phosphorylatable residues and the lack of cysteine. Its amino acid sequence shows that the N-terminal half is highly basic, while the acidic residues are located in the C-terminal part of the protein where more diversity in amino acids is noticed. The two transition proteins S1 and S2 share striking structural similarities. Few but significative similarities have been detected with the mammalian transition protein TP1 [Kistler, W. S., Noyes, C., Hsu, R. & Heinrikson, R. L. (1975) J. Biol. Chem. 250, 1847-1853], suggesting similar functions for all these proteins in chromatin remodeling during sperm differentiation. By contrast, the two dog-fish spermatid-specific proteins are structurally unrelated to sperm protamines and cannot be considered as their precursors.

Photoprotective effect of vitamins A and E on polyamine and oxygenated free radical metabolism in hairless mouse epidermis

The purpose of this study was to confirm the photoprotective effect on skin of vitamins A and E, due to inhibition of polyamine synthesis and production of free radicals. These variables were measured in the lumbar epidermis of the female hairless mouse subjected to UVA + B irradiation. Polyamines were assayed in epidermal homogenate by HPLC, and production of oxygenated free radicals was determined by spectrofluorometric assay of malonyl dialdehyde. It was determined that butyl-hydroxy-toluene and vitamin E inhibited production of free radicals (56% and 60%, respectively) and caused a significant reduction in polyamine biosynthesis (P less than 0.01), whereas the inhibitory effect of malonyl dialdehyde induced by vitamin A (30%) had no associated effect on polyamine metabolism.

Nuclear basic protein transition during sperm differentiation. Amino acid sequence of a spermatid-specific protein from the dog-fish Scylliorhinus caniculus

During dog-fish spermatogenesis, chromatin undergoes a continuous processing which involves two basic protein transitions: the first from somatic-type histones to spermatid-specific proteins and the second leading to protamines. Two spermatid-specific proteins S1 and S2 were isolated from nuclei of spermatid-enriched testis zone and the amino acid sequence of S1 has been determined. S1 contains 87 amino acids and has a molecular mass of 11179 Da. It is mainly characterized by a high content of basic residues (45%) and the presence of one residue of cysteine. Its primary structure shows that the N-terminal half is highly basic while the hydrophobic residues are preferentially localized in the C-terminal region. Three forms of S1 are present in testis which correspond to di-, mono- and nonphosphorylated molecules. This spermatid-specific protein shares no common structural feature with either histones and dog-fish protamines or rat spermatid-specific protein which has been previously described.

The structure of ubiquitinated histone H2B

Ubiquitinated histone H2B (uH2B) has been purified from both calf and pig thymus by exclusion chromatography in 7 M urea. Digestion of uH2B with Staphylococcus aureus V8 protease yielded the peptide 114-125 containing the ubiquitin moiety. Further digestion of this peptide with trypsin removed the ubiquitin and three H2B residues from the N-terminus. Edman degradations of both peptides established that ubiquitin is attached to the epsilon-amino group of lysine 120 in both calf and pig uH2B by an iso-peptide bond to the C-terminal glycine 76 of ubiquitin.

Primary structure of histone H2B from gonads of the starfish Asterias rubens. Identification of an N-dimethylproline residue at the amino-terminal

The complete amino acid sequence (121 residues) of histone H2B from gonads of the starfish Asterias rubens has been established from structural data obtained essentially from large fragments generated by cleavage of histone H2B at aspartyl residues and by limited hydrolysis of the dimer H2A-H2B with mouse submaxillary gland protease. No real sequence homology can be found between the amino-terminal sequence (residues 1-21) of starfish and calf H2B. One non-conservative substitution (serine-32 in calf----lysine-28 in starfish) leads to the presence of a cluster of eight basic residues (sequence 23-30) and to the disappearance of a potential site of phosphorylation. A particular structural feature of starfish histone H2B is the presence of N-dimethylproline at its amino-terminal end. By comparison with N-terminal acetylation, which is commonly found in histones, N-terminal methylation is rarely observed. At the present time the functional significance of the N-terminal methylation as well as that of the proline-rich nature of the amino-terminal sequence of the starfish histone H2B remain to be defined.

N-epsilon-acetylation of porcine mature erythrocytes ubiquitin

Highly purified of porcine mature erythrocytes ubiquitin were obtained according to the experimental procedure reported by Jabusch and Deutsch (1983). N-epsilon-acetylation in vitro of internal lysyl residues of ubiquitin by p-nitro-phenyl-acetate at pH 8.0 was performed. The extent of acetylation of ubiquitin was determined: about 4-5 residues (4.5 residues) of N-epsilon-lysine groups of ubiquitin were acetylated. We have assigned by Edman degradation the sites of acetylation and the sites of remaining free internal N-epsilon-lysine residues in the sequence: fully acetylated: Lys-6, Lys-11 and Lys-33. Partially free N-epsilon-lysine: Lys-27 and Lys-29 and probably Lys-48 and Lys-63. 50 cycles Edman degradation were performed on porcine ubiquitin and the first 45 N-terminal residues were identified. We have partially determined that the molecular conservation of 45 amino acid sequence of ubiquitin between cattle, man and swine since the 45 amino acid sequence out of 76 residues are identical. The amino acid composition between human and porcine ubiquitin are also identical.

Partial determination of the primary structure of a variant surface glycoprotein from Trypanosoma equiperdum. Composition and location of a carbohydrate moiety

Salivarian trypanosomes have the ability to evade the immune response of their hosts by the sequential expression of different cell surface glycoproteins. Among the isolated specific antigens from cloned variants of Trypanosoma equiperdum, a structural study was undertaken on two immunologically cross-reacting variant surface glycoproteins, and results concerning the basic antigenic type are reported. The glycoprotein was cleaved by cyanogen bromide, and amino acids of several purified fractions obtained by gel filtration chromatography of this cleavage mixture were sequenced by automated Edman degradation. Sequencing in particular allowed the identification of the N-terminal portion of the molecule (residues 1-74). Sugar compositions of the fractions have demonstrated the presence of at least two carbohydrate moieties in the glycoprotein. Using a subsequent enzymatic subcleavage we were able to locate the first glycosylation site in position 57. An important observation was that the first oligosaccharide identified was rich in mannose and devoid of galactose.

The amino-acid sequence of histone H2A from cuttlefish Sepia officinalis

The amino acid sequence of cuttlefish testis histone H2A (124 residues) was established from structural data obtained by automated sequencing of large peptides generated by the cleavage of the protein with V8 staphylococcal protease or by limited chymotryptic hydrolysis. Compared to the calf thymus homologous histone, cuttlefish H2A shows 14 substitutions (most of them conservative) and 5 deletions. Extensive evolutionary changes were mainly observed in the basic amino-terminal and carboxy-terminal regions of the molecule, which are the primary DNA-binding sites. Few punctual changes are observed in the central region (residues 18-118), which interacts strongly with histone H2B to form the dimer H2A-H2B.

Amino-acid sequence of an alpha-parvalbumin, pI = 4.88, from frog skeletal muscle

The primary structure of the most basic (pI = 4.88) of the two major parvalbumins from frog skeletal muscle (Rana esculenta) has been determined by partial automatic sequencing of the protein which exhibits a free N terminus, and a study of overlapping peptides obtained by cyanogen bromide cleavage and digestion with trypsin, thermolysin and Armillaria mellea protease. This protein shows the typical structure of an alpha-parvalbumin. Comparison of the primary structure of ion-binding loops of alpha and beta-parvalbumins does not provide a clear-cut explanation of their differences in ion-binding properties.

Proteolytic digestion studies of chromatin core-histone structure. Identification of limit peptides from histone H2B

Trypsin digestion of chicken erythrocyte chromatin results in a well-defined set of limit peptides derived from the core histones (P1-P5). Two peptides running in sodium dodecyl sulphate gel electrophoresis at the positions of P2 and P3 have been identified as histone H2B residues 21-125 and 24-125. No C-terminal residues are therefore lost from histone H2B. The N-terminal sequence removed correlates well with that having low sequence conservation and not with that showing the greatest basicity. The same correlation was reported previously by us for histone H2A.

Primary structure of the protamine isolated from the sperm nuclei of the dog-fish Scylliorhinus caniculus

A protamine was isolated from mature sperm nuclei of the dog-fish Scylliorhinus caniculus. It contains 31 amino acids per molecule and only five types of residues: arginine (20), glycine (6), serine (3), alanine (1) and tyrosine (1). The primary structure of this protamine is reported. The N-terminal sequence contains the four hydroxylated amino acids of the molecule; the C-terminal region shows a sequence of eleven adjacent residues of arginine and contains all the glycine residues present in the protein. The structure of this 'scylliorhinine' is compared to the amino acid sequence of other sperm protamines whose structure has been previously published. The presence of a modified tyrosine residue in some preparations is discussed in relation to sperm maturation.