Neuronal cell Thy-1 glycoprotein: homology with immunoglobulin

The amino acid sequences of mouse brain Thy-1 glycoproteins are shown to be homologous to those of variable-region immunoglobulin domains. There is also good homology with constant domains and beta 2-microglobulin; overall the results suggest that Thy-1 may be like the primordial immunoglobulin domain. Preliminary evidence for an invertebrate Thy-1 homolog supports this possibility.

Influence of chirality of amino acids on the growth of perceived taste intensity with concentration

Amino acids have markedly different taste properties depending upon their chirality and the structure of their side chains. They can modify the taste quality of foods in which they are found naturally or to which they are added depending on their concentrations. In this study, the influence of chirality of amino acids on the growth in perceived taste intensity with concentration was examined. Serial dilutions of 19 D-amino acids were presented to young subjects who indicated the relative intensities of the dilutions using the magnitude estimation procedure. The slopes of the psychophysical functions for 13 of the 19 D-amino acids which related log concentration and log perceived intensity were greater than the slopes for L-amino acids that have been reported in a previous study. The ratio (average slope D-amino acids)/(average slope L-amino acids) was found to be 1.21. The ratio of the slopes for individual enantiomers bears some relationship to taste quality. No conclusive relationships between the slopes of the psychophysical functions were found with chemical structure of thresholds, however. Implications for receptor mechanisms and nutrition are discussed.

Isolation, characterization and N-terminal sequences of the CNBr-cleavage peptides from human complement Factor B. Localization of a free thiol group and a sequence defining the site cleaved by factor D

Nine CNBr-cleavage peptides from Factor B (a component of the alternative pathway of complement) were isolated. Each was characterized by amino acid analysis and automated Edman degradation. One peptide contained a methionyl bond resistant to cleavage by CNBr. The number of CNBr-cleavage peptides is in agreement with the results of amino acid analysis of Factor B and the fragments Ba and Bb. A total of 358 unique residues were identified from the N-terminal sequences of the CNBr-cleavage peptides. These represent approx. 50% and 60% of the total residues of Factor B and fragment Bb respectively. Alignment of two CNBr-cleavage peptides (CB-VIc and CB-IV) provided a continuous segment of 140 residues. This sequence contained the site cleaved by Factor D to generate the Ba and Bb fragments during the activation of complement. Peptide CB-IV contained a free thiol group at a position corresponding to residue 33 of fragment Bb. Amino sugar analyses of Factor B and of fragments Bb and Ba indicated that all the carbohydrate structures of factor B are N-linked to asparagine through N-acetylglucosamine. The two carbohydrate-attachment sites of the Bb fragment were identified.

The catalytic chain of human complement subcomponent C1r. Purification and N-terminal amino acid sequences of the major cyanogen bromide-cleavage fragments

1. The a- and b-chains of reduced and alkylated human complement subcomponent C1r were separated by high-pressure gel-permeation chromatography and isolated in good yield and in pure form. 2. CNBr cleavage of C1r b-chain yielded eight major peptides, which were purified by gel filtration and high-pressure reversed-phase chromatography. As determined from the sum of their amino acid compositions, these peptides accounted for a minimum molecular weight of 28 000, close to the value 29 100 calculated from the whole b-chain. 3. N-Terminal sequence determinations of C1r b-chain and its CNBr-cleavage peptides allowed the identification of about two-thirds of the amino acids of C1r b-chain. From our results, and on the basis of homology with other serine proteinases, an alignment of the eight CNBr-cleavage peptides from C1r b-chain is proposed. 4. The residues forming the 'charge-relay' system of the active site of serine proteinases (His-57, Asp-102 and Ser-195 in the chymotrypsinogen numbering) are found in the corresponding regions of C1r b-chain, and the amino acid sequence around these residues has been determined. 5. The N-terminal sequence of C1r b-chain has been extended to residue 60 and reveals that C1r b-chain lacks the 'histidine loop', a disulphide bond that is present in all other known serine proteinases.

Human complement component C4. Structural studies on the fragments derived from C4b by cleavage with C3b inactivator

1. One of the activation products of C4, C4b, was prepared, and the reactive thiol group on the alpha'-chain was radioactively labelled with iodo[2-14C]acetic acid. The alpha'-chain was isolated and the N-terminal amino acid sequence of the first 13 residues was determined. 2. C4b was cleaved by C3bINA in the presence of C4b-binding protein and C4d and C4c isolated. The radioactive label and therefore the reactive thiol group were located to C4d. 3. C4c was reduced and alkylated and the two alpha'-chain fragments of C4c were separated. 3. The molecular weights, amino acid analyses and carbohydrate content of the three alpha'-chain fragments were determined. C4d has a mol.wt. of 44500 and a carbohydrate content of 6%. The two alpha'-chain fragments of C4c have mol.wts. of 25000 (alpha 3) and 12000 (alpha 4) and carbohydrate contents of 10 and 22% respectively. 4. The N-terminal amino acid sequences of C4d, the alpha 3 and the alpha 4 fragments were determined for 18, 24 and 11 residues respectively and, by comparison with the N-terminal sequence of the C4b alpha'-chain, the 25000-mol.wt. fragment (alpha 3) was shown to be derived from the N-terminal part of the alpha'-chain. 5. C-Terminal analyses were done on the alpha'-chain and its three fragments. Arginine was found to be the C-terminal residue of C4d and of the alpha 3 fragment. The C-terminal residue of the alpha'-chain and of the alpha 4 fragment could not be identified. The order of the three fragments of the alpha'-chain is therefore: alpha 3(25000)--C4d(44500)--alpha 4(12000). The specificity of C3bINA is for an Arg--Xaa peptide bond.

Amino acid sequence around the thiol and reactive acyl groups of human complement component C4

Activation of the fourth component of complement (C4) by C1s results in the generation of a reactive acyl group, able to react with putrescine, and in the release of a free thiol group that cannot be detected in the native haemolytically active molecule. Both the reactive acyl group and the free thiol group have been shown to reside in C4d, a fragment of the alpha'-chain of C4b derived from digestion of the molecule with the control proteins C3b inactivator and C4-binding protein. Peptides derived from CNBr digestion of [1,4-14C]putrescine-labelled and iodo(2-14C]acetic acid-labelled C4d have been obtained and used to establish a continuous sequence of 88 residues from the N-terminus of the molecule. The thiol and reactive acyl groups are contained in an octapeptide that shows near identity with the equivalent sequences reported for alpha 2-macroglobulin and C3. Other adjacent short sections also show homology of sequence between the three proteins, and it is highly likely that they contribute to the overall structure that gives a unique reactivity to the thiol ester bond postulated to exist in the native forms of the three proteins.

Structure of the zeta chain of human embryonic hemoglobin

The complete amino acid sequence of the zeta chain of human embryonic hemoglobin has been determined. It differs from human alpha globin at 57 of the 141 residues and several of the replacements are at positions of structural or functional importance, particularly in relationship to the Bohr effect and high intrinsic oxygen affinity which are characteristic of embryonic hemoglobins. The zeta-globin sequence is more closely related to other mammalian embryonic alpha-like globins than to human alpha, suggesting that there have been strong selective pressures to maintain these embryo-specific globins since their emergence several hundred million years ago.

Clr and Cls subcomponents of human complement: two serine proteinases lacking the 'histidine-loop' disulphide bridge

The N-terminal amino acid sequence of human C1s b chain has been extended to 52 residues. The histidine residue involved in the charge-relay system is located at position 38, whereas the histidine-loop disulphide bridge is missing. So far, human complement sub-components C1r and C1s are the only known mammalian serine proteinases lacking this disulphide bridge.

Amino acid sequence around the proposed thiolester bond of human complement component C4 and comparison with the corresponding sequences from C3 and alpha 2-macroglobulin

The amino acid sequence around the proposed thiolester bond in human complement component C4 has been determined. The sulphydryl and reactive acyl groups involved in the intrachain thiolester bond are contained in a short section of sequence which shows almost complete identity with the equivalent sequence from alpha 2-macroglobulin and C3. Other regions of homology between the three proteins near the proposed thiolester bond are also apparent.

Rat brain Thy-1 glycoprotein. The amino acid sequence, disulphide bonds and an unusual hydrophobic region

The full sequence of the Thy-1 membrane glycoprotein of rat brain is reported. The sequence was determined from tryptic and V-8 proteinase peptides and consisted of 111 amino acids. The amino terminus was blocked and consisted of a pyroglutamic acid residue. The molecule contained two disulphide bonds, namely Cys-9--Cys-111 and Cys-19--Cys-85. Three N-linked amino sugars were located at Asn-23, Asn-74 and Asn-98. In each case the sequence on the C-terminal side of the attachment point was Asn-Xaa-Thr as would be expected for N-linkage. The C-terminal peptides were unusual, in that they were either obtained in a highly aggregated form, or could only be purified after binding to Brij 96 micelles. Thus they appeared to have hydrophobic properties, yet did not contain any extended sequence of hydrophobic amino acids. Other unusual features of the C-terminal peptides were the presence of unidentified ninhydrin-positive material and of glucosamine and galactosamine. The C-terminal residue has not been directly identified but Cys-111 is the last conventional amino acid. It is suggested that the hydrophobic properties of the C-terminal peptides may be due to the linkage of lipid. The sequence of the Thy-1 glycoprotein showed homologies with immunoglobulin domains. This relationship is examined in detail in the paper following [Cohen et al. (1981) Biochem. J. 193, 000--000].

Partial sequence of human complement component factor B: novel type of serine protease

Factor B (a component of the alternative pathway of complement) is believed to contain the proteolytic site of the complex enzymes C3 convertase (C3bB) and C5 convertase (C3bnB). Conflicting results have been obtained in regard to the inactivation of these enzymes by diisopropyl phosphorofluoridate but it has been suggested that activated Factor B (Factor B) is a serine protease with the active site in Bb, a COOH-terminal fragment of approximately 60,000 molecular weight. Partial amino acid sequence studies of Bb derived from human Factor B have shown that the NH2-terminal 40 residues have no homology with NH2-terminal sequences of other serine proteases. However, positioning of a further 170 residues out of approximately 290 residues in two continuous CNBr fragments from the COOH terminus has shown that there is a strong homology of sequence in this section. The active site residues histidine, aspartic acid, and serine all are present in positions corresponding with those of typical serine proteases. It is suggested that Factor B is a novel type of serine protease with a catalytic chain of molecular weight twice that of proteases previously studied and probably with a different activation mechanism.

Factor D of the alternative pathway of human complement. Purification, alignment and N-terminal amino acid sequences of the major cyanogen bromide fragments, and localization of the serine residue at the active site

The serine esterase factor D of the complement system was purified from outdated human plasma with a yield of 20% of the initial haemolytic activity found in serum. This represented an approx. 60 000-fold purification. The final product was homogeneous as judged by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis (with an apparent mol.wt. of 24 000), its migration as a single component in a variety of fractionation procedures based on size and charge, and its N-terminal amino-acid-sequence analysis. The N-terminal amino acid sequence of the first 36 residues of the intact molecule was found to be homologous with the N-terminal amino acid sequences of the catalytic chains of other serine esterases. Factor D showed an especially strong homology (greater than 60% identity) with rat 'group-specific protease' [Woodbury, Katunuma, Kobayashi, Titani, & Neurath (1978) Biochemistry 17, 811-819] over the first 16 amino acid residues. This similarity is of interest since it is considered that both enzymes may be synthesized in their active, rather than zymogen, forms. The three major CNBr fragments of factor D, which had apparent mol.wts. of 15 800, 6600 and 1700, were purified and then aligned by N-terminal amino acid sequence analysis and amino acid analysis. By using factor D labelled with di-[1,3-14C]isopropylphosphofluoridate it was shown that the CNBr fragment of apparent mol.wt. 6600, which is located in the C-terminal region of factor D, contained the active serine residue. The amino acid sequence around this residue was determined.

Bradykinin-induced renal hemodynamic alterations: renin and prostaglandin relationships

The present studies examined the role of the renin-angiotensin system as a modifier of the renal vasomotor response to bradykinin. Renal arterial bradykinin infusion (80 ng.kg-1.min-1) initially resulted in increased renal blood flow (RBF). The secretory rates of renin and prostaglandins increased after 60 min. With continued bradykinin administration (120 min) RBF and prostaglandin secretory rates returned toward control values, although renin secretory rate remained elevated (P less than 0.02). After prostaglandin synthetase inhibition, RBF decreased and bradykinin administration returned RBF to control values. Prostaglandin secretory rates decreased after meclofenamate (P less than 0.005). Continued bradykinin infusion resulted in a return of the renin secretory rate to control values. The administration of bradykinin after competitive inhibition of angiotensin II resulted in a sustained increase in renal blood flow. These results suggest that the initial bradykinin-induced renal hyperemia is only partially dependent on enhanced prostaglandin release, the increase in renin secretion by bradykinin infusion after prostaglandin synthetase inhibition is consistent with a bradykinin and renin interaction, and the lack of a sustained hyperemia after bradykinin is related to increased renin-angiotensin system activity.

Investigation of antibodies against Fasciola hepatica in moose Alces americana

A serological investigation was carried out to check the presence of antibodies against Fasciola hepatica in a collection of 125 sera moose Alces americana killed in the Province of Quebec. As revealed by hemagglutination tests, two moose had titers suggesting contact with this parasite.

NH2-terminal sequence of the chick proalpha1(I) chain synthesized in the reticulocyte lysate system. Evidence for a transient hydrophobic leader sequence

Translation of chick procollagen mRNA in a reticulocyte lysate system yields a larger proalpha1(I) chain than is observed in vivo. The NH2-terminal sequence of this putative precursor, determined by automated radiosequencing, is Met-Phe-Ser-Phe-Val-X-Ser-Arg-Leu-Leu-Leu-Leu-Ile-Ala-Ala-X-X-Leu-Leu. This sequence closely resembles the transient hydrophobic leader (signal) sequences observed on most secreted proteins. When synthesized in the presence of microsomal membranes from dog pancreas, which contain signal peptidase activity, proalpha chains with the electrophoretic mobility of underhydroxylated procollagen polypeptides synthesized in vivo are produced. Estimates of the molecular weight of the NH2-terminal extension of the precursor suggest that the leader sequence may be longer than those commonly found in precursors of secreted proteins.

Comparison of the NH2-terminal sequence of ovalbumin as synthesized in vitro and in vivo

The sequence of the NH2-terminal 35 residues of chicken ovalbumin was found to be identical with that of the product translated in vitro from the corresponding mRNA. Together with our previous results (Palmiter, R.D., Gagnon, J., and Walsh, K.A. (1978) Proc. Natl. Acad. Sci. U.S.A. 75, 94-98), these data show that the only co-translational processing event at the NH2 terminus of the primary translation product is the replacement of the initiator methionine by an acetyl group. Thus, secretion of this major protein by chick oviduct does not involve the cleavage of a "signal peptide" as is characteristic of three other egg white proteins secreted by the same cells.

Ovalbumin: a secreted protein without a transient hydrophobic leader sequence

Ovalbumin mRNA was translated in a reticulocyte lysate. The primary translation product starts with methionine derived from Met-tRNAf. When the nascent polypeptide is about 20 residues long, this methionine is removed. The new NH2-terminal glycine is acetylated from acetyl-CoA when the polypeptide is 44 residues long. The sequence of 35 residues at the NH2 terminus of ovalbumin was determined by automated Edman degradation after a method was devised to prevent acetylation during protein synthesis in the reticulocyte lysate. This sequence is the same as that of secreted ovalbumin and does not resemble the transient "signal peptides" associated with most secretory proteins, including three other egg white proteins synthesized in the same cells as ovalbumin.