PubMed Health⌕ Search

Biomedical subjects

A G Diamond

Publications and source records attributed to A G Diamond.

30 records · Page 2Linked to original sources
PubMed1992

The sequence of the flavoprotein subunit of bovine heart succinate dehydrogenase.

The cDNA sequence of the flavoprotein subunit of bovine heart succinate dehydrogenase is reported. This is the first complete eukaryotic sequence of the flavoprotein subunit to be characterized, and it encodes a 665-amino acid protein that consists of a presequence and a 621-residue mature protein. The deduced bovine sequence shows homology to the corresponding peptides of prokaryotic succinate dehydrogenase and the related fumarate reductases; in particular, there is good overall homology (48%) to the flavoprotein subunit of Escherichia coli succinate dehydrogenase. The conserved sequences comprising the active site and those involved in FAD binding are also found in the bovine protein. The active site of the bovine polypeptide contains a cysteine that confers sensitivity of the enzyme to sulfhydryl reagents; this cysteine is only present in some sequences and thus provides a discriminatory biochemical marker. A putative flavoprotein subunit of human placental succinate dehydrogenase (partial sequence) that lacks this critical cysteine (Malcovati, M., Marchetti, T., Zanelli, T., and Tenchini, M. L. (1991) in Flavins and Flavoproteins 1990 (Curti, B., Ronchi, S., and Zanetti, G., eds) pp. 727-730, Walter de Gruyter & Co., Berlin) has only 16% homology to the bovine heart flavoprotein subunit. However, we show that the enzyme from human placenta is as sensitive to N-ethylmaleimide as that from bovine tissues. In addition, a transcript in human placenta and muscle hybridizes to the bovine heart flavoprotein cDNA and is the same size as that in bovine tissues.

Amino Acid Sequence↗
PubMed1992

Cloning and expression of class I major histocompatibility complex genes of the rat.

Little is known about the organization of class I genes in the rat although there is prima facie evidence that it is distinct from that of the mouse. We report the cloning of 61 nonclassical rat class I genes into cosmid clusters with a total mapped length of 1,264 kb. It is certain that the total number of class I genes in the rat must exceed this number. From restriction maps it is possible to identify substantial regions of duplication. By transfection of cosmids into mouse L cells, it has been possible to demonstrate at least seven different nonclassical rat class I genes that are expressible on the cell surface. Crossreaction of a single mouse monoclonal antibody with all of these class I molecules is consistent with sequence homogenization within the rat nonclassical system. Attempts to find rat homologues of the mouse Tla genes by crosshybridization of rat cosmids with a range of different TLa-specific probes were unsuccessful, suggesting that this large group of divergent class I genes is absent or nearly so from the rat. The large number of class I genes in the rat appears to have arisen by expansion of genes more closely related to the classical sequence.

Animals↗
PubMed1991

Class II major histocompatibility complex genes of the sheep.

The class II genes of the sheep major histocompatibility complex (MHC) have been cloned from two unrelated heterozygous sheep into cosmid vectors. By restriction mapping and hybridization with a number of class II probes of human and mouse origin, the cloned genetic material has been assigned to seven distinct alpha genes, 10 distinct beta genes and 14 beta-related sequences. It was difficult to identify homologues of specific HLA class II genes because of a tendency for the ovine genes to cross-hybridize between HLA probes representing different loci. Such cross-hybridization was especially marked among the beta genes. While DQ and DR homologues have been tentatively identified by several criteria, no genes corresponding to DP have been identified. Cosmids containing class II alpha and beta genes have been transfected into mouse LTK- cells, and surface expression of a sheep class II molecule has been obtained.

Animals↗
PubMed1989

A trans-acting major histocompatibility complex-linked gene whose alleles determine gain and loss changes in the antigenic structure of a classical class I molecule.

The RT1.A locus of the rat MHC encodes the H chain of the single classical class I molecule of this species. One of the alleles of this polymorphic locus, RT1.Aa, is present in several laboratory inbred, congenic, and MHC recombinant rat strains. Studies of the RT1.Aa class I molecule from a number of these strains as a target for CTL show that its antigenicity, both as an alloantigen and a restricting element, is subject to gain and loss alterations by the action of a gene mapping in the MHC to the right of RT1.A. This locus is apparently present in two allelic forms (one possibly a null allele) corresponding to the presence or absence of a dominant transacting modifier, and has been named class I modification, or cim. The antigenic change brought about by cim is scarcely detectable serologically but highly immunogenic for CTL. Biochemical investigations show that cim affects the post-translational modification of RT1.Aa.

Alleles↗
PubMed1989

The class II genes of the rat MHC.

Genes that encode class II Ag from the MHC of the rat, the RT1 region, have been isolated as a series of cosmid clones. The cosmids define two clusters, each of which contains three identifiable sequences; one homologous to alpha-chain and two to beta-chain genes. Both the serologically identified rat class II Ag have been expressed in mouse L cell fibroblasts after the introduction of each alpha-chain gene along with a beta-chain gene from the same cluster. There are substantial homologies to the I region of the mouse H-2 complex in the presence, location, orientation, and expression of the six identified sequences from the rat RT1, supporting the view that the overall organization of the two gene complexes has remained conserved since the species separated.

Animals↗
PubMed1986

Differential expression of RT1 class II genes in fibroblast cell lines: recognition by allogeneic and xenogeneic T lymphocytes.

A cosmid (cos a 13.1) containing RT1 class II B alpha and B beta genes was introduced into mouse and rat fibroblast cell lines by transformation. Mouse L cells transformed with cos a 13.1-synthesized cell surface class II molecules that were similar, with respect to apparent molecular weight and binding of xenogeneic- and allogeneic-specific antibodies, to class II molecules on rat B cells. RT1 class II molecules on the surface of mouse L cells were recognized by both allogeneic and xenogeneic T cells. In contrast, rat-2 cells transformed with cos a 13.1 did not synthesize any detectable RT1 class II molecules at the cell surface, and the levels of B alpha and B beta mRNA were generally very low or undetectable. This differential expression of exogenous class II genes was not exclusively due to a trans-acting positive regulatory factor in L cells. Other possible explanations for this difference are discussed.

Animals↗
PubMed1984

The alloantigenic organization of RT1Aa, a class I major histocompatibility complex molecule of the rat.

Over 300 monoclonal IgG alloantibodies have been prepared against RT1Aa , the class I major histocompatibility complex molecule of the DA rat. In this study a combination of techniques is exploited to show that all these antibodies can be allocated to 9 antigenic sites which form a continuous antigenic surface, that is, no site is completely isolated from the rest. The results suggest that techniques for the identification of antigenic sites using competitive inhibition of monoclonal antibody binding are generally valid, in the sense that competition between antibodies appears most commonly to represent competition between combining sites for a structural feature of the antigenic surface. From the distribution of antibodies between sites, it is clear that the RT1Aa molecule has three immunogenic areas against which nearly all the antibodies studied were directed. Of these areas one is both antigenically complex, consisting of four closely spaced sites, and remarkably immunodominant. Antibodies directed at sites between the major areas are extremely rare.

Animals↗
PubMed1984

Localized conformational changes induced in a class I major histocompatibility antigen by the binding of monoclonal antibodies.

We describe two monoclonal antibodies, R3/47 and YR1/1, directed against different epitopes of the expressed rat class I major transplantation antigen RT1Aa, that interact with each other so that the binding of one antibody, YR1/1, is greatly enhanced by the binding of the other. The positive interaction between R3/47 and YR1/1 also occurs when using RT1Aa molecules solubilized from cell membranes in detergent. It is therefore unlikely that the molecular environment of the membrane contributes to the interaction. The ability of R3/47 to modify the YR1/1 determinant on the RT1Aa molecule is mediated without any significant loss of potency by highly purified monomeric Fab fragments. This result suggests that the binding of R3/47 to the RT1Aa molecule alters the YR1/1 determinant by initiating a propagated conformational change in the antigen.

Animals↗
PubMed1982

Blood:bone disequilibrium. VI. Studies of the solubility characteristics of brushite: apatite mixtures and their stabilization by noncollagenous proteins of bone.

Recent evidence of the occurrence of brushite in newly formed bone mineral prompted a study of the solubility properties of brushite:apatite mixtures under physiological conditions and the influence on them of pH, lactate, pyruvate, and, particularly, noncollagenous bone proteins (NCBPs). Brushite alone was surprisingly stable in solution at pH 7.4, 37 degrees C. In the presence of increasing amounts of apatite, hydrolysis of brushite to an insoluble phase occurred. A decrease of 0.1 pH unit or the addition of 1.5 mM pyruvate or 10 mM lactate increased the ion activity product (Ca2+ x HPO4(2-) 3 or more times. However, within the loose envelope of bone such conditions so different from those in the circulation might be only local or temporary. NCBPs, on the other hand, stabilized brushite in solution alone as well as in the presence of apatite for days. They probably act by adsorbing strongly to the crystal surface and preventing nucleation by apatite. This brushite-apatite-bone protein system exhibits solubility characteristics that can resolve the old problems presented by the participation of the skeleton in extracellular calcium homeostasis on the one hand, and by the apparent insolubility of the apatite mineral of bone on the other.

Animals↗
PubMed1982

The acidic macromolecules in rabbit cortical bone tissue.

Rabbit cortical bone powder was extracted with EDTA solutions at neutral pH and the soluble constituents fractionated by DEAE-cellulose chromatography. The acidic fractions obtained were further investigated by gel chromatography and chemical analysis. Two classes of proteoglycans were present; one containing chondroitin sulphate and the other containing material resembling keratan sulphate mixed with a smaller amount of chondroitin sulphate. Sialoglycoproteins were detected by specific chemical introduction of tritium label into the sialic acid residues of the acidic glycoprotein fraction. Following sodium dodecyl sulphate-polyacrylamide gel electrophoresis and fluorography, the presence of numerous distinct sialoglycoprotein components was demonstrated.

Animals↗
PubMed1980

Blood/bone disequilibrium: IV. Reciprocal effects of calcium and phosphate concentrations on ion fluxes.

Quantitative measurements were made of the ion fluxes of calcium and phosphate into and from calvaria (mouse or rat) when clamped in specially designed micro-Ussing chambers. The effects of varying concentrations of calcium were examined on the influx and efflux of calcium and of its counterion, phosphate. A comparable series of experiments was performed with varying phosphate concentrations. Both ions, as their concentrations increased, depressed their own influx, increased their own efflux, and significantly increased the equilibrium concentration, E/K, supported by the calvaria. Similarly, both ions, as their concentrations increased, affected the influx or efflux of their counterion only slightly but did depress the counterion's equilibrium level, E/K, significantly. In spite of these changes it was shown that calvaria effectively buffered the medium at physiological concentrations of calcium and phosphate. The buffering capacity, however, was small, and the balance, E/K, was modified by small uptake or loss of either ion. The small size of the interacting mineral pool was confirmed by direct measurement of the rapidly exchanging fractions of both calcium or phosphate. They were only approximately 1% of the total ions present. The significance of these findings is discussed.

Animals↗