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Biomedical subjects

I D Walker

Publications and source records attributed to I D Walker.

At least 145 records · Page 8Linked to original sources
PubMed1986

Fractionation of detergent lysates of cells by ammonium sulphate-induced phase separation.

A procedure is described for fractionating detergent lysates of cells based on the ability of (NH4)2SO4 to induce phase separation of detergents such as Triton X-100, sodium deoxycholate, and sodium cholate, into detergent-rich and detergent-depleted phases. An analysis of six murine lymphocyte cell surface molecules revealed that the partitioning in Triton X-100 of each molecule was highly dependent upon the (NH4)2SO4 concentration, each antigen partitioning into the detergent-rich phase at a defined salt concentration. In contrast, none of the six molecules appeared in the detergent-rich phase of a Triton X-114 phase separation, even though two of the molecules, namely Ly-2/3 and L3T4, are well-characterized integral membrane proteins. It was also observed that (NH4)2SO4 resulted in the partitioning of many nonmembrane proteins into the detergent-rich phase, indicating that the procedure can be used to fractionate all cellular proteins. By judicious choice of (NH4)2SO4 concentrations, precipitation of cellular proteins at two different (NH4)2SO4 concentrations, and combining the method with subcellular fractionation prior to detergent solubilization, substantial enrichment and concentration of particular cellular proteins could be achieved.

Ammonium Sulfate↗
PubMed1986

The W and L allelic forms of phenylalanine hydroxylase in the rat differ by a threonine to isoleucine substitution.

High performance liquid chromatography maps of tryptic and chymotryptic peptides from the W and L forms of rat phenylalanine hydroxylase differed by one peptide. Sequencing of the variant tryptic peptides showed a substitution of threonine in the W form by isoleucine in the L form and this same difference was confirmed in the chymotryptic peptides. This allelic substitution would result from a nucleotide change of ACA to ATA at amino acid position 371 of the full phenylalanine hydroxylase sequence. Altered sodium dodecyl sulphate binding is postulated to explain the change in mobility of the proteins observed on sodium dodecyl sulphate/polyacrylamide gels.

Alleles↗
PubMed1986

Deletion of 24 amino acids from the pro-alpha 1(I) chain of type I procollagen in a patient with the Ehlers-Danlos syndrome type VII.

A child with the type VII form of the Ehlers-Danlos syndrome was shown to have a structural defect in the amino terminus of the pro-alpha 1(I) chain of type I procollagen. Normal and mutant amino-terminal cyanogen bromide peptides (pN-alpha 1(I) CB0,1 peptides) were purified from the medium of the patient's cultured fibroblasts. Amino acid sequencing of tryptic peptides derived from the mutant pN-alpha 1(I) CB0,1 peptide showed that an expected sequence of 24 amino acids (positions 136-159 of the normal pN-alpha 1(I) CB0,1 peptide) was deleted. The segment deleted from the mutant pro-alpha 1(I) chain contains the small globular region of the NH2-propeptide, the procollagen N-proteinase cleavage site, the NH2-telopeptide, and first triplet of the helix of the alpha I(I) collagen chain (Chu, M.-L., de Wet, W., Bernard, M., Ding, J.F., Morabito, M., Myers, J., Williams, C., and Ramirez, F. (1984) Nature 310, 337-340). Loss of the procollagen N-proteinase cleavage site from the mutant pro-alpha 1(I) chain accounted for the persistence of its NH2-propeptide despite normal production of the N-proteinase by cultured mutant fibroblasts. Collagen production by mutant fibroblasts was doubled possibly due to reduced feedback inhibition by the NH2-propeptides. The child appeared to be heterozygous for the peptide deletion and, as the parents did not show any evidence of the deletion, it is likely that the child had a new mutation of one allele of the pro-alpha 1(I) gene. The deleted peptide corresponds precisely to the sequence coded by exon 46 of the normal pro-alpha 1(I) gene (Chu, M.-L., de Wet, W., Bernard, M., Ding, J.F., Morabito, M., Myers, J., Williams, C., and Ramirez, F. (1984) Nature 310, 337-340).

Amino Acids↗
PubMed1986

Triton X-114 phase separation of platelet membrane glycoproteins from normal subjects and a patient with type I thrombasthenia.

Surface-labelled normal and thrombasthenic platelets have been subjected to phase separation in Triton X-114. Triton-rich and Triton-poor fractions have been analysed by SDS-PAGE and IEF-SDS-PAGE. Partitioning characteristics of the major glycoproteins have been defined. The Triton-rich fraction contained GPIIb, III, IV, VI, VII, VIII, GP38 and the IIb beta subunit. In contrast, the Triton-poor fraction contained the HMWGP, GPIa, Ib, IIb, III, V and GPIX. Analysis of the platelet membrane glycoproteins of a patient with Type 1 thrombasthenia has been carried out using Triton X-114. The value of the method in diagnosis of this condition and differences between our findings and those published previously are discussed.

Blood Platelet Disorders↗
PubMed1986

Partial primary structure of the T4 antigens of mouse and sheep: assignment of intrachain disulfide bonds.

The T4 antigens of mouse and sheep have been purified to homogeneity and partially sequenced using protein and peptide microsequencing techniques. Both mouse and sheep antigens bear distinct homology to human T4, having an amino-terminal segment that is homologous to the K-chain variable region (VK). A surprisingly high degree of sequence divergence was nevertheless evident between the T4 antigens of the three mammalian species, suggesting an unusually rapid rate of evolution that is possibly related to the functional role of T4 in class II major histocompatibility complex antigen recognition. The mouse and sheep T4 antigens contain at least three intrachain disulfide bonds which in all cases connect adjacent cysteine residues. All three intrachain disulfide linkages are situated within the putative extracellular domain, and the amino-terminal disulfide bond probably involves the two cysteine residues homologous to those which form the intrachain bridge within the VK domain of immunoglobulin molecules. The structural relationship of the T4 antigen to other members of the immunoglobulin supergene family is discussed.

Amino Acid Sequence↗
PubMed1986

The murine Fc receptor for immunoglobulin: purification, partial amino acid sequence, and isolation of cDNA clones.

The murine Fc receptor for IgG (Fc gamma R) was purified to homogeneity by immunoaffinity chromatography from detergent lysates of the macrophage cell line J774. Microsequencing of intact protein yielded a single amino-terminal sequence, which was confirmed and extended to 20 residues by the isolation of an overlapping peptide. The isolation of additional proteolytic fragments obtained by using Staphylococcus aureus V8 protease, cyanogen bromide, and lysine C proteinase, facilitated sequence analysis of a total of 119 amino acid residues. Codon usage charts were used to construct oligonucleotide probes based on the amino acid sequences of three nonoverlapping peptides. These probes were used to screen a cDNA library derived from the WEHI-3B myelomonocytic cell line, and a single cDNA clone (pFc24) to which all three probes hybridized was isolated. This clone, containing a 1.02-kilobase cDNA insert, has been characterized by restriction mapping and partial DNA sequencing, and it has been shown to encode the Fc gamma R. The sequence at the 5' end of the clone contained the coding information for the amino-terminal sequence of the Fc gamma R as well as a putative 13-amino acid signal sequence. The 3' end of the clone encoded a peptide identified in purified receptor preparations. Thus, the presence of coding information at the 5' and 3' ends of this clone suggests that full-length Fc receptor cDNA spans greater than 1 kilobase.

Amino Acid Sequence↗
PubMed1986

An international and interregional comparison of haemostatic variables in the study of ischaemic heart disease. Report of a working group.

Levels of haemostatic variables that may be involved in thrombogenesis have been compared in groups of men of similar mean age in communities at very low (Gambia), high (England and Czechoslovakia) or very high (Scotland and Finland) risk of ischaemic heart disease (IHD). There was a consistent gradient of higher factor VII levels with higher IHD risk and also suggestive gradients in the case of two other vitamin K dependent factors, factors II and X. Mean platelet counts were lower and mean fibrinolytic activity was greater in Gambian men than in European men. There was a suggestive though not entirely consistent association between mean fibrinogen levels and IHD risk in the groups from IHD-endemic countries. The results as a whole, and particularly those on factor VII, strengthen the case for the increasingly detailed epidemiological as well as laboratory investigation of the role of the haemostatic system in thrombogenesis and IHD.

Adult↗
PubMed1986

The development of thyrotoxicosis (Graves' disease) during immunosuppression for autoimmune haemolytic anaemia.

A patient is described who developed thyrotoxicosis (Graves' disease) during immunosuppressive therapy for acquired autoimmune haemolytic anaemia. The fact that the two conditions may be associated should be recognised. Long-term immunosuppressive therapy does not prevent the development of immunoglobulins of IgG type postulated to be aetiologically involved in Graves' disease.

Adult↗
PubMed1985

Effect of Ciprofibrate on platelet aggregation and fibrinolysis in patients with hypercholesterolaemia.

The fibrinolytic and platelet effects of Ciprofibrate, a new lipid lowering drug, were studied in 7 patients with hypercholesterolaemia over a 12 week period. A significant reduction in plasma fibrinogen was noted and a lesser increase in fibrinolytic activity. However, no change in platelet aggregation was noted. As expected Ciprofibrate produced a significant hypolipidaemic effect in these patients. We have described effects of Ciprofibrate which may have potential benefits in this high risk patient group.

Adult↗
PubMed1985

The effect of the synthetic steroid Org OD14 on fibrinolysis and blood lipids in postmenopausal women.

Two groups of postmenopausal women were compared. One group of 13 was given the synthetic steroid Org OD14 to suppress climacteric symptoms and one group of 14 was given placebo. After a 2 week baseline period the subjects received daily for 12 weeks, either 2.5 mg Org OD14 or placebo. There were no significant differences between the groups pre-treatment. Compared with the placebo group, during treatment, the Org OD14 group showed the following significant differences: higher haemoglobin, haematocrit, platelet count, plasminogen, fibrinolytic activity on fibrin plates and antithrombin III and lower fibrinogen. No significant differences between the groups were found in alpha 2 antiplasmin levels, total cholesterol, total triglycerides, bilirubin or transaminase levels but the Org OD14 group had significantly lower levels of HDL cholesterol. With the exception of the haemoglobin and haematocrit levels all of the differences had disappeared by 2 weeks post treatment.

Adult↗