PubMed Health⌕ Search

Biomedical subjects

E J Walker

Publications and source records attributed to E J Walker.

26 records · Page 2Linked to original sources
PubMed1978

Preparation of allosteric ribonuclease.

A method for the preparation of allosteric ribonuclease from bovine pancreas is described. The effects of freeze-drying ribonuclease from acid and alkaline solutions on plots of velocity versus substrate concentration for the hydrolysis of 2':3'-cyclic CMP are examined. Comparison of these plots with the plots obtained with severeal commercial enzyme preparations indicates that the conformation of the enzyme is dependent on the method of preparation. Aging experiments demonstrate that further conformational changes occur at different rates, depending on the methods of storage. Results suggest that the allosteric behaviour of ribonuclease has not always been observed with commercial preparations, owing to variations in methods of preparation and storage of the enzyme.

Allosteric Site↗
PubMed1978

A procedure for obtaining initial estimates of parameters appearing in steady-state rate or equilibrium binding equations.

A "peeling" procedure is described for obtaining initial estimates of the parameters in the equation: formula: (see text), where P(x) and Q(x) are polynomials in x. The method is illustrated, in the context of enzyme kinetics, using data which are fitted to the following equation: formula: (see text), where v denotes the initial steady-state velocity at an initial substrate concentration S, and a1, a2, b1, and b2 are non-negative constants. The applicability and limitations of the method for data fitting in fields such as enzyme kinetics and ligand-binding studies are discussed.

Carboxypeptidases↗
PubMed1976

Further evidence for an allosteric model for ribonuclease.

Evidence is presented from three experimental systems to support the allosteric model of Walker et al. (1975) (Biochem. J. 147, 425-433) which explains the substrate-concentration-dependent transition observed in the RNAase (ribonuclease)-catalysed hydrolysis of 2':3'-cyclic CMP (cytidine 2':3'-cyclic monophosphate). 1. Kinetic studies of the initial rate of hydrolysis of 2':3'-cyclic CMP show that the midpoint of the transition shifts to lower concentrations of 2':3'-cyclic CMP in the presence of the substrate analogues 3'-CMP, 5'-CMP, 3'-AMP, 3'-UMP and Pi; 2'-CMP and 2'-UMP do not cause such a shift. 2. Trypsin-digestion studies show that a conformational change in RNAase to a form less susceptible to tryptic inactivation is induced in the presence of the substrate analogues 3'-CMP, 5'-CMP, 3'-AMP, and 3'-UMP. 2'-CMP, 2'-AMP and 2'-UMP do not induce this conformational change. 3. Equilibrium-dialysis experiments demonstrate the multiple binding of molecules of 3'-CMP, 3'-AMP and 5'-AMP to a molecule of RNAase. 2'-CMP binds the ratio 1:1 over the analogue concentration range studied.

Adenosine Monophosphate↗
PubMed1975

An allosteric model for ribonuclease.

Data from two assay systems show that the kinetics of the hydrolysis of cytidine 2':3'-cyclic monophosphate by bovine pancreatic RNAase (ribonuclease) is not consistent with conventional models. An allosteric model involving a substrate-dependent change in the equilibrium between two enzyme conformations is proposed. Such a model gives rise to a calculated curve of velocity versus substrate concentration which fits the experimental data. The model is also consistent with the results of an examination of the tryptic digestion of RNAase. Substrate analogues are able to protect RNAase against hydrolysis by trypsin and the percentage of RNAase activity which remains after digestion increases sigmoidally as the analogue concentration is increased. The model also explains the pattern seen in the Km values quoted in the literature and is consistent with strong physical evidence for a ligand-induced conformational change for RNAase reported in the literature.

Allosteric Site↗
PubMedDate not supplied

Polydermatomyositis with anti-PL7 antibody: clinical and laboratory follow-up over a five year period.

Anti-PL7 antibodies to threonyl-tRNA synthetase purified from beef liver were observed in the serum of a dermatopolymyositis patient. They were identified by CIE and DID using a standard anti-PL7 antiserum and quantified by ELISA in serum samples taken over a five year period. The level of antibodies against not only threonyl-tRNA synthetase but also several muscle proteins including tropomyosin, was strongly correlated with disease activity and treatment. This correlation may prove important both in monitoring the response of the patient to treatment and to our understanding of the aetiology of the disease.

Amino Acyl-tRNA Synthetases↗