Partial characterization of human complement factor H by protein and cDNA sequencing: Homology with other complement and non-complement proteins

Factor H, a control protein of the human complement system, is closely related in functional activity to two other complement control proteins, C4b-binding protein (C4bp) and complement receptor type 1 (CR1). C4bp is known to have an unusual primary structure consisting of eight homologous units each about 60 amino acids long. Such units also occur in the N-terminal regions of the complement proteins C2 and factor B, and in the non-complement serum glycoprotein ₂I. Amino acid sequencing, and sequencing of a factor H cDNA clone, show that factor H also contains internal repeating units, and is homologous to the proteins listed above.     

5''-Nucleotidase activity and adenosine formation in stimulated, hypoxic and underperfused rat heart.

Changes in 5'-nucleotidase activity were calculated on the basis of alterations in ATP, ADP, phosphocreatine, Pi, Mg2+, IMP and AMP, determined by using 31P n.m.r. spectroscopy and h.p.l.c., during isoprenaline infusion, graded hypoxia and graded underperfusion in isolated rat heart. Calculated activity changes were compared with the total efflux of purines (adenosine + inosine + hypoxanthine) in order to assess the involvement of various 5'-nucleotidases in formation of adenosine. Purine efflux exhibited an exponential relation with cytosolic [AMP] during isoprenaline infusion and hypoxia (r = 0.92 and 0.95 respectively), supporting allosteric activation of 5'-nucleotidase under these conditions. Purine efflux displayed a linear relation with cytosolic [AMP] during graded ischaemia (r = 0.96), supporting substrate regulation in the ischaemic heart. The calculated activities of membrane-bound ecto-5'-nucleotidase were similar to the observed relations between purine efflux and cytosolic [AMP] in all hearts. The calculated activities of the ATP-activated cytosolic and lysosomal enzymes and of the ATP-inhibited cytosolic 5'-nucleotidase could not explain the observed release of purines under the conditions examined. These results indicate that the kinetic characteristics of the membrane-bound ecto-enzyme are consistent with an important role in the formation of extracellular adenosine, whereas the characteristics of the other 5'-nucleotidases are inconsistent with roles in adenosine formation under the conditions of the present study.     

Limbness in the early chick embryo lateral plate

In order for the limb to be useful in the evaluation of early determinants of morphogenesis, it is necessary to understand some of the characteristics associated with "limbness" and, more importantly at the beginning at least, it is necessary to know what regions of the early embryo exhibit limbness qualities. Previous investigators have assumed, without direct experimental evidence, that the flank does not have limbness qualities, even at early stages of development. However, there are a few studies suggesting that the early flank does possess limbness qualities. The purpose of the present study was to determine how extensively the qualities of limbness exist in the early chick embryo. Tissues from the future neck, wing, flank, and leg regions were grafted to host celoms and evaluated for their abilities to form limbs. Limbs developed from all four regions of stage 11-14 embryos, but after stage 14 only grafts from the wing and leg regions formed limbs.     

Amylin and the amylin gene: structure, function and relationship to islet amyloid and to diabetes mellitus

Amylin, the major peptide component of the islet amyloid commonly found in the pancreases of patients with type 2 (non-insulin-dependent) diabetes mellitus (NIDDM), is a recently discovered islet polypeptide. This peptide has many structural and functional features suggesting that it is a novel hormone, which may control carbohydrate metabolism in partnership with insulin and other glucoregulatory factors. Amylin is synthesised in, and probably secreted from, the beta-cells of the islets of Langerhans, where it has recently been immunolocalised to secretory granules. DNA cloning studies indicate that in the human and the rat, amylin is generated from a precursor, preproamylin, which displays a typical signal peptide followed by a small prohormone-like sequence containing the amylin sequence. The presence of the signal peptide suggests that amylin is secreted and plays a physiological role. Amylin is probably generated by proteolytic processing similar to that for proinsulin and other islet prohormones. The human amylin gene encodes the complete polypeptide precursor in two exons which are separated by an intron of approx. 5 kb, and is located on chromosome 12. Amylin is a potent modulator of glycogen synthesis and glucose uptake in skeletal muscle, and is capable of inducing an insulin-resistant state in this tissue in vitro, and perhaps also in the liver in vivo. In normal metabolism, amylin could act in concert with insulin as a signal for the body to switch the site of carbohydrate disposal from glycogen to longer-term stores in adipose tissue, by making skeletal muscle relatively insulin-resistant, whilst at the same time leaving rates of insulin-stimulated carbohydrate metabolism in adipose tissue unaltered. Several lines of evidence now implicate elevated amylin levels in the pathogenic mechanisms underlying NIDDM, and suggest to us that the obesity which frequently accompanies this syndrome is a result of, rather than a risk factor for, NIDDM. Following the beta-cell destruction which occurs in type 1 (insulin-dependent) diabetes mellitus (IDDM), it is probable that amylin secretion disappears in addition to that of insulin. As patients with insulin-treated IDDM frequently experience problems with hypoglycaemia, and as amylin acts to modulate the action of insulin in various tissues, it is possible that amylin deficiency may contribute to morbidity in insulin-treated IDDM, perhaps through the loss of a natural damping mechanism which guards against hypoglycaemia under conditions of normal physiology.     

The MRC OX-45 antigen of rat leukocytes and endothelium is in a subset of the immunoglobulin superfamily with CD2, LFA-3 and carcinoembryonic antigens.

The MRC OX-45 cell surface antigen is a glycoprotein of 45,000 apparent mol. wt of rat leukocytes and endothelium. Antibodies against the antigen inhibit T lymphocyte responses by stimulation of suppression by accessory cells. We now report the immunochemical characterization of this antigen and its cDNA sequence. The predicted protein sequence contains 240 amino acids including a leader sequence of 22 residues and a carboxy-terminal sequence of 23 residues that is replaced in the processed molecule by a glycosyl-phosphatidylinositol anchor attached at serine 195. Two Ig-related domains are predicted to account for all of the processed sequence and the circular dichroism spectrum shows pure beta-structure. The amino-terminal domain is V-like, but without a disulphide bond, while the second domain is C-like (C2-SET) with two disulphide bonds. The sequence matches particularly well with the extracellular parts of LFA-3 and CD2 antigens and the first two domains of carcinoembryonic antigen and non-specific, cross-reacting antigen.     

Processing of histidine transfer RNA precursors. Abnormal cleavage site for RNase P

The 5'-terminal guanylate residue (G-1) of mature Escherichia coli tRNA(His) is generated as a result of an unusual cleavage by RNase P (Orellana, O., Cooley, L., and S?ll, D. (1986) Mol. Cell. Biol. 6, 525-529). We have examined the importance of the unique acceptor stem structure of E. coli tRNA(His) in determining the specificity of RNase P cleavage. Mutant tRNA(His) precursors bearing substitutions of the normal base G-1 or the opposing, potentially paired base, C73, can be cleaved at the +1 position, in contrast to wild-type precursors which are cut exclusively at the -1 position. These data indicate that the nature of the base at position -1 is of greater importance in determining the site of RNase P cleavage than potential base pairing between nucleotides -1 and 73. In addition, processing of the mutant precursors by M1-RNA or P RNA under conditions of ribozyme catalysis yields a higher proportion of +1-cleaved products in comparison to the reaction catalyzed by the RNase P holoenzyme. This lower sensitivity of the holoenzyme to alterations in acceptor stem structure suggests that the protein moiety of RNase P may play a role in determining the specificity of the reaction and implies that recognition of the substrate involves additional regions of the tRNA. We have also shown that the RNase P holoenzyme and tRNA(His) precursor of Saccharomyces cerevisiae, unlike their prokaryotic counterparts, do not possess these abilities to carry out this unusual reaction.     

Use of animals with unknown ancestries in scientifically managed breeding programs

Whether to incorporate animals with unknown ancestries as founders into scientifically managed captive breeding programs, can be a difficult decision. If the animals are offspring of known founders, their inclusion in the breeding program will result in an increased incidence of inbreeding in the captive population. If the animals are additional founders, excluding them from the breeding program will result in the loss of valuable genetic variation. In general, the practice in scientifically managed captive breeding programs is to exclude animals with unknown ancestries to avoid possible inbreeding. A method of estimating the cost of making an incorrect decision on whether to use animals of unknown ancestry as founders both in terms of lost genetic variation and increased inbreeding is presented. It was determined that the loss of genetic variation resulting from excluding founders is always greater than the loss of genetic variation caused by unequal founder line representation resulting from including related animals, as if they were founders. In addition, the increased rate of accumulation of inbreeding resulting from excluding founders will eventually overcome the initial inbreeding resulting from including related animals. However, in some cases, it will take a substantial number of generations for this to occur, and the benefits of possible lowered future expected inbreeding may never be realized. The decision concerning whether to use animals with unknown ancestry should, therefore, be based on the estimated relative costs of making an error, in terms of both lost genetic variation and expected future inbreeding, rather than on avoiding the immediate possibility of increased inbreeding alone. Two examples using studbook data are given to show how this method can be practically applied to the management of captive populations. © 1993 Wiley-Liss, Inc.     

Evidence for the aerobic degradation of tetrachloroethylene by a bacterial isolate

Summary A microorganism, which utilizes tetrachloroethylene (PCE) as a sole source of metabolic carbon under aerobic conditions, has been isolated. It has been identified as aPseudomonas spp. Degradation of PCE by this bacterium was quantified by gas chromatography.