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Biomedical subjects

S G Williams

Publications and source records attributed to S G Williams.

At least 73 records · Page 4Linked to original sources
PubMed1993

Early catalytic steps of Euglena gracilis chloroplast type II fatty acid synthase.

Euglena gracilis is a very ancient eukaryote whose chloroplast acquisition and evolution has been independent of higher plants. The organism in unique in possessing two de novo fatty acid synthases, a true multienzyme complex of great size in the cytosol and a plastid-localized type II fatty acid synthase composed of discrete enzymes and acyl carrier protein (ACP). The enzymology of the early steps of fatty acid biosynthesis differed in the Euglena type II fatty acid synthase compared to those of Escherichia coli and plants. The enzymes of Euglena participating in both priming and elongation reactions to form a new carbon-carbon bond were acetyl-CoA-ACP transacylase, malonyl-CoA-ACP transacylase, and beta-ketoacyl-ACP synthase I. The effects of inhibitors on the three different enzymes were noted. All carbon-carbon bond formation was inhibited by cerulenin. Although neither fatty acid biosynthesis nor any of the isolated enzymes were sensitive to diisopropylphosphofluoridate, the three Euglena enzymes studied were sensitive to different sulfhydryl-alkylating agents. Acetyl-ACP supported fatty acid biosynthesis as effectively as did comparable amounts of ACPSH and acetyl-CoA. There was no evidence for a beta-ketoacyl-ACP synthase III for priming such as has been reported in type II fatty acid synthase of higher plants and bacteria. The roles of the acetyl-CoA-ACP transacylase and beta-ketoacyl-ACP synthase I appear to be unique in the type II fatty acid synthase of Euglena. Acetyl-CoA-ACP transacylase, malonyl-CoA-ACP transacylase, and beta-ketoacyl-ACP synthase I were separated from one another and shown to have different molecular weights.

3-Oxoacyl-(Acyl-Carrier-Protein) Synthase↗
PubMed1993

Comparison of acyl-carrier protein and other protein structures in aqueous solutions by Fourier-transform infrared spectroscopy.

Protein solution structures were analyzed by horizontal attenuated total reflectance (ATR) FTIR spectroscopy. Secondary structure compositions determined from analyses of amide-I and II region and amide-III region difference spectra were compared. Data for proteins of known solution structure, cytochrome c, concanavalin A and lysozyme, were compared with those reported in the literature. Melittin, a peptide from bee venom whose secondary structural configuration varies depending upon solution conditions was also examined. Acyl-carrier protein (ACP) is a small protein of recognized dynamic structure that in its diverse physiologic roles interacts specifically with numerous different proteins. Horizontal ATR FTIR analysis of ACP's secondary structure indicated a predominantly helical structure best defined as a combination of ordered and disordered helices. The FTIR-derived structural composition agreed with those determined for ACP by other techniques. Comparison of independent analyses of the amide-I and III regions to determine protein configuration compositions was a useful method of verifying the internal consistency of the calculated structural compositions of dynamically-structured proteins.

Acyl Carrier Protein↗
PubMed1993

The transcriptional activator HlyU of Vibrio cholerae: nucleotide sequence and role in virulence gene expression.

HlyU upregulates expression of the haemolysin, HlyA, of Vibrio cholerae. DNA sequence analysis indicates that HlyU is an 11.9 kDa protein containing a putative helix-turn-helix motif and belonging to a family of small regulatory proteins, including NoIR (Rhizobium meliloti), SmtB (Synechococcus PCC 7942) and ArsR (plasmids R773, Escherichia coli; pI258, Staphylococcus aureus; and pSX267, Staphylococcus xylosus). An hlyU mutant was constructed by insertional inactivation, and found to be deficient in the production of both the haemolysin and a 28 kDa secreted protein. The mutant was assessed for virulence in the infant mouse cholera model, revealing a 100-fold increase in the LD50. This suggests that HlyU promotes expression of virulence determinant(s) in vivo.

Amino Acid Sequence↗
PubMed1992

Complete dissection of the Hb(64-76) determinant using T helper 1, T helper 2 clones, and T cell hybridomas.

We have generated cloned Th1 cells, Th2 cells, and T cell hybridomas specific for the single immunogenic peptide from the beta-chain of murine hemoglobin (Hb(64-76)). The availability of these various types of T cells provided us an unique opportunity to examine and dissect the T cell response to an immunogenic peptide. A panel of altered Hb peptides was made by replacing each amino acid in the Hb peptide (positions 64-76) with a conservative amino acid substitution or an alanine. Although none of the eleven T cell clones and hybridomas tested exhibited the same pattern of reactivity to the substituted Hb peptides, some general features were identified for all T cell responses. The primary T cell contact residue of Hb(64-76) was shown to be asparagine 72. For every Hb(64-76) specific T cell, no activation was observed using a peptide containing the conservative substitution of a glutamine for the asparagine at position 72. The flanking glutamic acid at position 73 was also required for a proliferative response for all of the Th1 and Th2 clones. The Th subtypes were not grossly unique in their responses to the substituted Hb peptides, but exhibited minor differences in fine specificity with the Th1 cells identifying more critical amino acids then did the Th2 cells. For the Th1 cells and also the T cell hybridomas, the phenylalanine at position 71 was critical for a T cell response. Analysis of peptide affinity for IEk molecules indicated that position 71 played a role in peptide binding to MHC. Secondary T cell contact residues, which were important for many but not all of the T cells, were identified at positions 69, 70, and 76. Overall T cell responses were minimally affected by changes in the amino acid residues at positions 64-68, 74, and 75. We have also demonstrated that cloned Th1 cells, Th2 cells and T hybridomas can be generated against the same Hb(64-76) determinant.

Amino Acid Sequence↗
PubMed1992

Liver and biliary problems in cystic fibrosis.

There have been striking advances in the management of complications of cirrhosis in the 50 years since biliary cirrhosis was recognised as a feature occurring in a minority of patients with cystic fibrosis. Many questions remain unanswered with regard to its pathogenesis, its effect on other systems, morbidity and mortality and to its optimum management. Factors which may initiate liver disease and/or cause progressive biliary fibrosis leading to biliary cirrhosis in some cystic fibrosis patients are being defined but much is still poorly understood and further research is required. Clinical and pathological studies confirm that cirrhosis is frequently asymptomatic and only slowly progressive, with the prevalence rising with age. In a recent large epidemiological study, however, it was found that the age related prevalence fell in patients over the age of 20 years although deaths from liver disease were rare. Does the presence of liver disease cause premature respiratory death in teenagers? Current treatments control variceal bleeding, the important sequel for most patients with biliary cirrhosis, with less morbidity and mortality than in the past but require reappraisal as newer techniques become available. Endoscopic radiologically controlled methods are emerging as an important adjunct to the surgical control of biliary complications which cause symptoms in up to 4%. Ursodeoxycholic acid improves liver function tests but its effect on hepatic fibrosis and portal hypertension will only be demonstrated by large scale prospective controlled trials. Should liver transplantation have a larger role in management? In this chapter we have attempted to summarise the current state of knowledge and to assess the efficacy of present management.

Biliary Tract Diseases↗
PubMed1992

Molecular analysis of the lac operon encoding the binding-protein-dependent lactose transport system and beta-galactosidase in Agrobacterium radiobacter.

The genes coding for the binding-protein-dependent lactose transport system and beta-galactosidase in Agrobacterium radiobacter strain AR50 were cloned and partially sequenced. A novel lac operon was identified which contains genes coding for a lactose-binding protein (lacE), two integral membrane proteins (lacF and lacG), an ATP-binding protein (lacK) and beta-galactosidase (lacZ). The operon is transcribed in the order lacEFGZK. The operon is controlled by an upstream regulatory region containing putative -35 and -10 promoter sites, an operator site, a CRP-binding site probably mediating catabolite repression by glucose and galactose, and a regulatory gene (lacl) encoding a repressor protein which mediates induction by lactose and other galactosides in wild-type A. radiobacter (but not in strain AR50, thus allowing constitutive expression of the lac operon). The derived amino acid sequences of the gene products indicate marked similarities with other binding-protein-dependent transport systems in bacteria.

Amino Acid Sequence↗
PubMed1992

Typhus and typhuslike rickettsiae associated with opossums and their fleas in Los Angeles County, California.

The recent discovery of cat fleas (Ctenocephalides felis) infected with a typhuslike rickettsia (designated the ELB agent) raises the question of whether similar rickettsial infections exist in wild cat flea populations. We verified the presence of the ELB agent and Rickettsia typhi in urban and suburban areas of Los Angeles, Calif. Opossums trapped in close proximity to the residences of human murine typhus cases in Los Angeles county and other areas within the city of Los Angeles were tested for the presence of typhus group rickettsiae by the polymerase chain reaction (PCR). The presence of rickettsiae in the spleen tissues of three opossums (n = 9) and in 66 opossum fleas (n = 205) was determined by PCR and was verified by dot blot and Southern transfer hybridization. Further analysis of the amplified PCR products generated by a series of primer pairs derived from either the 17-kDa antigen gene or the citrate synthase gene revealed that both R. typhi and the ELB agent were present in the tested samples. Dual infection was not noted in the samples; however, the fleas were infected with either R. typhi or the ELB agent. The presence of the ELB agent in the cat flea population may have implications for public health. Whether this agent is responsible for the mild cases of human murine typhus in urban and suburban areas of Los Angeles or in other endemic foci remains to be determined.

Animals↗
PubMed1992

Endoscopic therapy for bile duct stones in a geriatric population.

During the 5 year period to May 1988, 137 consecutive patients (age range, 65-102 years; median 84 years) with a diagnosis of choledocholithiasis, were referred to The Middlesex Hospital Geriatric Department. Endoscopic sphincterotomy was successful in 96.2% of cases and immediate biliary drainage was achieved in all but one of these patients. Stones were cleared endoscopically in 73.3% and surgically in 4.7% of cases. Long-term stenting was employed in 14.3% of patients. The 30 day mortality after endoscopic or surgical treatment was 4.7% (six deaths), although death was probably unrelated to therapy in half the cases. Deaths were due to procedural cardiorespiratory arrest (1), pancreatitis (1), pneumonia (2) and cerebrovascular accident (2). Endoscopic treatment is effective even in a high-risk geriatric population. After sphincterotomy patients with intact gall bladders should be managed expectantly.

Aged↗
PubMed1992

Research considerations: family opinions about elderly relatives in research.

As the elderly population expands due to longer life expectancy, clinical investigation will be required to provide optimal care. Family members of the elderly often become involved in the decision to participate in clinical investigation due to moral, ethical, personal, and financial concerns. Establishing rapport with the patient and family members is of great importance for the nurse when conducting clinical investigation. Most relatives interviewed for this study had positive opinions toward research with the elderly.

Aged↗
PubMed1991

Transcription of the Vibrio cholerae haemolysin gene, hlyA, and cloning of a positive regulatory locus, hlyU.

Transcription of the Vibrio cholerae hlyA gene, which encodes a cytotoxic haemolysin, has been investigated. The hlyA transcript initiates 430 nucleotides (nt) upstream of the translational start site. hlyA-cat transcriptional fusion constructs were active in V. cholerae but not in Escherichia coli. An hlyA-cat fusion was used to select, from a V. cholerae O17 plasmid library, a clone that could activate the hlyA promoter in E. coli. This regulatory locus has been designated hlyU. hlyU appears to be distinct from the previously described hlyR locus.

Bacterial Proteins↗
PubMed1991

T cell inducing determinants contain a hierarchy of residues contacting the T cell receptor.

T cells through their antigen specific T cell receptor recognize a bi-molecular ligand composed of an antigenic peptide bound to a MHC molecule. Several T cell inducing determinants have been extensively characterized by single amino acid substitutions. In this review, we have summarized our characterization of four immunodominant determinants. Each of these determinants possessed a single amino acid residue which was absolutely critical for the recognition by T cells. From these data we propose a hypothesis that there is a hierarchy in the T cell contact residues of a determinant, composed of a single primary residue, and a few secondary residues.

Amino Acid Sequence↗
PubMed1990

Acyl carrier protein interacts with melittin.

Acyl carrier protein (ACP) from Escherichia coli has been shown to form complexes with melittin, a cationic peptide from bee venom. ACP is a small (Mr 8847), acidic, Ca2(+)-binding protein, which possesses some characteristics resembling those of regulatory Ca2(+)-binding proteins including interaction with melittin. Complexing between melittin and ACP which occurred both in the presence and absence of Ca2+ was evident by chemical cross-linking the two peptides, fluorescence changes (including anisotropy measurements), and inhibition by melittin of the activity of a nonaggregated fatty acid synthetase from Euglena. Also, anti-Apis mellifera antibodies which contained antibodies against melittin specifically inhibited the same enzyme system activity relative to non-immune IgG.

Acyl Carrier Protein↗
PubMed1990

Constipation in the long-term care facility.

In the long-term care facility, constipation is a problem of clinical significance. An awareness of the types and specific causes of constipation, such as underlying medical conditions and side effects of medication, can facilitate management of these patients. Problems unique to long-term care patients also need to be addressed. This review emphasizes that constipation in these patients needs to be addressed individually and that regular inservice education can optimize nursing care.

Constipation↗
PubMed1989

The 56 kDa protein of human genital skin fibroblasts is identical to that radiolabelled by [3H]dihydrotestosterone 17 beta-bromoacetate.

Analysis of soluble proteins from human genital skin fibroblasts by two-dimensional polyacrylamide gel electrophoresis reveals an abundant protein doublet of mol. wt 56,000 with isoelectric points (pI) of 6.7 and 6.5. This protein is absent in non-genital skin fibroblasts as well as in genital skin fibroblasts of most patients with complete forms of androgen insensitivity. The protein specifically binds androgen. A protein of similar estimated molecular weight (58,000) from human genital skin fibroblasts has recently been found to be covalently radiolabelled by the affinity ligand dihydrotestosterone 17 beta-bromoacetate (DHT-BA). In the present study these proteins have been found to be indistinguishable on one- and two-dimensional gel electrophoresis. Antibodies raised against the 56 kDa pI 6.7/6.5 protein also recognized the protein covalently radiolabelled by DHT-BA. A third protein of estimated mol. wt 59,000 has been found to be associated with several steroid hormone receptor complexes but has no known ligand binding activity. This protein was found to be clearly separable from the 56/58 kDa protein on two-dimensional gel electrophoresis as it has a more acidic pI of approximately 5.4. Furthermore, antibodies against the 59 kDa protein do not recognize the 56 kDa species, and vice versa.

Affinity Labels↗