Biomedical subjects
Publications and source records attributed to M Adam.
The specificity constant, kcat/Km, for the hydrolysis of hippuryl-mercaptoacetate by crystals of the Streptomyces R61 D-D peptidase was measured by reaction of the thiol produced with 4,4'-dithiodipyridine. The values of kcat/Km for the crystal and in solution were the same (within experimental error). A novel method for treating the lag in the progress curves was developed.
Among the active-site-serine penicillin-recognizing proteins, the Streptomyces R61 extracellular DD-peptidase is the only one to have a His-Thr-Gly sequence [instead of Lys-Thr(Ser)-Gly] in 'box' VII. The His residue was replaced by Gln or Lys. Both mutations induced a marked decrease in the rates of both tripeptide substrate hydrolysis and acylation by benzylpenicillin and cephalosporin C. The rate of hydrolysis of the thioester hippuryl thioglycollate was less affected. The most striking result was the disproportionate loss of transpeptidation properties by both mutants, indicating an important role of His-298 in this reaction. We believe that this result represents the first modification of a DD-peptidase leading to a specific decrease of the transpeptidation-to-hydrolysis ratio.
The replacement of bone defects is very important in clinical practice. This study compares biological properties of poly(2-hydroxyethyl methacrylate)-collagen composite with those exhibited by pure p(HEMA), an insoluble fraction of calf skin collagen (ISC-40) and demineralized bone matrix after implantation into pig or dog femurs. The levels of biodegradation or destruction of implants and healing of bone defects were studied using X-ray photography, histology and enzyme histochemistry. The results indicated a significant effect of collagen on biological destruction of the p(HEMA)-composite implants; even a minute amount of collagen influences this process dramatically. A stimulatory action of collagen on new bone formation may be of importance in bone defect healing.
Thirty-eight patients with refractory or relapsed non-Hodgkin's lymphoma (19 patients) or Hodgkin's disease (19 patients) were treated with salvage therapy. The peripheral stem cell collection was performed during hematologic recovery after myeloablative chemotherapy. In eight patients with Hodgkin's disease the number of CFU-GM collected was less than 0.5 x 10(4)/kg and these patients were excluded for stem cell transplantation. In the remaining 30 patients, a median of 4 x 10(4) CFU-GM/kg was collected (range 0.8-100 x 10(4)/kg) by three leukaphereses in 25 patients and six to 11 leukaphereses in five patients. Conditioning regimens were CBV (eight), BEAM (six), BEAC (10) and cyclophosphamide + total body irradiation (TBI) (six). Without TBI, the mean time for reaching a granulocyte count greater than 0.5 x 10(9)/l was 18 days and for a platelet count greater than 50 x 10(9)/l was 19 days in 23 out of 24 patients. With TBI, in five patients the mean time for reaching a granulocyte count greater tahn 0.5 x 10(9)/l was 37 days and for a platelet count greater than 50 x 10(9)/l was greater than 100 days. Complications were minor. There was only one toxic death. The outcome in these patients was similar to that observed in patients who received autologous bone marrow transplantation for advanced lymphomas. In conclusion, we observed good hematologic recovery except when TBI was used in the conditioning regimen.
5-Lipoxygenase-activating protein (FLAP) is specifically labeled by [125I]L-669,083 and [125I]L-691,678, photoaffinity analogues of two classes of potent leukotriene biosynthesis inhibitors. Because human FLAP contains only a single tryptophan residue at position 72 and two internal methionine residues at positions 89 and 125, we have used reagents that specifically cleave at these residues, in conjunction with antipeptide antisera, to localize the site of attachment of the photoaffinity ligands. Immunoprecipitation of specifically labeled peptide fragments after digestion of photoaffinity-labeled FLAP by iodosobenzoic acid at 72Trp demonstrates that the inhibitors bind to FLAP amino-terminal to this residue. This finding is consistent with similar immunoprecipitation studies after digestion at methionine residues using cyanogen bromide. These findings localize the site of attachment of the inhibitors to a region of FLAP that includes the hydrophilic loop between the proposed first and second transmembrane regions. Based on these findings, site-directed mutagenesis of human FLAP was performed to define key amino acids involved in inhibitor binding. Using a radioligand binding assay, analysis of mutants of human FLAP expressed in COS-7 cells demonstrates that a number of residues in the amino-terminal half of the first hydrophilic loop of the protein can be deleted without significantly affecting inhibitor binding. In contrast, no inhibitor binding was detectable with mutants in which amino acid residues in the carboxyl-terminal half of this loop were deleted. Furthermore, a point mutation of 62Asp to asparagine results in a mutant with dramatically reduced affinity for inhibitors. This loss of affinity was not displayed by a mutant in which 62Asp was mutated to a glutamate residue, suggesting that a negative charge associated with residue 62 may be critical for inhibitor binding. The roles that amino acid residues in the carboxyl-terminal half of the first hydrophilic loop of FLAP may play in the binding of leukotriene biosynthesis inhibitors are currently under investigation.
The cDNA encoding the voltage-gated chloride channel from the electric organ of Torpedo californica has been isolated and sequenced. The 2.7 kilobase pair cDNA encodes an 810 amino acid polypeptide which is highly homologous at both the DNA (97%) and amino acid (97%) levels to the voltage-gated chloride channel from the electric organ of T. marmorata. The majority of the 24 amino acid differences between the T. californica and T. marmorata voltage-gated chloride channels are clustered in two putative cytoplasmic domains with six differences located between residues 10-92 and 14 differences occurring between residues 576 to 708. Only one amino acid difference occurs in one of the predicted transmembrane domains. The most dramatic difference is an insertion of Asp-Val-Pro-Gly in a large cytoplasmic domain at amino acid residue 627 of the T. californica channel.
Thioester substrates can be used to study the hydrolysis and transfer reactions catalysed by beta-lactamases and DD-peptidases. With the latter enzymes, accumulation of the acyl-enzyme can be detected directly. The efficiency of various amines as acceptor substrates was in excellent agreement with previous results obtained with peptide substrates of the DD-peptidases. The results indicated the presence of a specific binding site for the acceptor substrates. Although most of the results agreed well with a simple partition model, more elaborate hypotheses will be needed to account for all the data presented.
The high-molecular-mass penicillin-binding proteins (HMM-PBPs), present in the cytoplasmic membranes of all eubacteria, are involved in important physiological events such as cell elongation, septation or shape determination. Up to now it has, however, been very difficult or impossible to study the catalytic properties of the HMM-PBPs in vitro. With simple substrates, we could demonstrate that several of these proteins could catalyse the hydrolysis of some thioesters or the transfer of their acyl moiety on the amino group of a suitable acceptor nucleophile. Many of the acyl-donor substrates were hippuric acid or benzoyl-D-alanine derivatives, and their spectroscopic properties enabled a direct monitoring of the enzymic reaction. In their presence, the binding of radioactive penicillin to the PBPs was also inhibited.
The human gene for the recently identified 5-lipoxy-genase-activating protein (FLAP) has been cloned. The gene was isolated from two different genomic libraries and is contained within four overlapping bacteriophage clones. The gene spans greater than 31 kilobases and consists of five small exons and four large introns. Southern blot analysis of human genomic DNA suggests the presence of a single FLAP gene per haploid genome. A restriction site polymorphism was identified in intron II of the gene. This restriction fragment length polymorphism appears to be present in the normal population at a fairly high frequency. The transcription initiation site was located, at an adenine residue, 74 base pairs upstream of the ATG initiation codon. Examination of the sequence of the gene 5' to the mRNA start site revealed the presence of a possible TATA box (TGTAAT) 22 base pairs upstream and potential AP-2 and glucocorticoid receptor binding sites. Functional analysis of the FLAP gene promoter was assayed by transient transfection of mouse P388D1 cells (macrophage) and human HepG2 cells (hepatoma) with 5'-flanking sequences of the FLAP gene fused upstream of the chloramphenicol acetyltransferase reporter gene. Expression in the mouse macrophage cell line of the various FLAP gene promoter constructs revealed both tissue specificity and enhancer-like activities whereas in the hepatoma cell line only a minimum level of activity was obtained.
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Samples of linear (additionally crosslinked) p(HEMA) with different amounts of fibrillar collagen were implanted into the popliteal region of rats. After 3 month, the implanted materials were harvested and examined by SEM. The implants underwent marked structural or morphological changes. While the fibrillar collagen was readily resorbed by invading cells, the synthetic constituent persisted to biodegradation. The p(HEMA) residues were shaped into spherical particles, approx. 1-15 microns in diameter. The possible fate of these microparticles in the host organism is discussed.
The effects of some antirheumatics on the formation and retraction of collagen lattices seeded with fibroblasts have been studied. Among the antirheumatics, diclofenac was the most active inhibitor of lattice retraction, then tropesin and to a lesser extent indomethacin. Ibuprofen which is known as a very slight inhibitor of protein synthesis was able to significantly enhance lattice retraction when 10 micrograms/ml (48.5 microM) and 50 micrograms/ml (242 microM) were used.
The authors present a survey of visualization of the individual types of collagen by the metal replica technique, special attention was paid to the visualization of type IX collagen, which, together with type XI, is a minor component of cartilage collagen. The molecule of this collagen type contains three collagen and four non-collagen domains and during the isolation involving pepsin digestion it is cleaved into MHW and LMW fragments. The HMW fragment can be further cleaved into shorter and longer arm. Results of statistical evaluation of 199 measured molecular fragments showed the following length: whole molecule 194 +/- 23 nm, HMW 136 +/- 16 nm, the longer arm of the HMW 87 +/- +/- 12 nm and the LMW of shorter arm of the HMW 43 +/- 9 nm.
The authors investigated the intensity of collagen synthesis in patients subjected to operation or re-operation of a total endoprosthesis of the hip joint. The patients suffered from osteoarthritis, rheumatoid arthritis and ankylosing spondylitis. The authors assessed the activity of collagen glucosyl transferase (S-GGT) and the concentration of the N-terminal propeptide procollagen type III by two methods (S-Pro III-N-P and S-Fab) in serum before and after operation. A significant rise of S-GGT and S-Fab, as compared with controls, occurred only after operation while S-Pro III-N-P was elevated already before operation. S-GGT did not differ before and after operation, while N-propeptide concentration rose when either method was used.
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Children with leukocyte adherence deficiency (LAD) exhibit heterogeneous defects in the leukocyte integrin CD18 subunit that prevent surface expression of functional CD11/CD18 leukocyte integrin adherence complexes. We used a retroviral vector, designated LCD18SN, to transfer the CD18 cDNA into K562 human myeloid leukemia cells and into EBV B-cells from a child with LAD. Transfer of the LCD18SN retroviral construct, which expresses the CD18 cDNA from the Moloney Murine leukemia virus (MoMLV) long terminal repeat (LTR), into K562 cells resulted in relatively high levels of CD18 mRNA and intracellular protein. Retroviral-mediated gene transfer of CD18 into LAD EBV B-cells resulted in low, but readily measurable, levels of surface expression of the CD11a/CD18 complex in these previously deficient lymphocytes. The reconstitution of surface expression of the CD11a/CD18 complex by gene transfer of the CD18 cDNA into LAD EBV B-cells indicates that this syndrome represents a candidate disorder for gene therapy.
Various ester and thioester derivatives of hippuric acid have been prepared which were substrates of both beta-lactamases and DD-peptidases. The thioesters were more rapidly hydrolysed by nearly all the enzymes. Surprisingly, the enzymes acted rather efficiently on substrates which did not contain any chiral centre.
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