Heterogeneous proteolytic specificity and activity of the house dust mite proteinase allergen Der p I

Background Exposure of the skin or respiratory tract to proteinases is frequently associated with allergic sensitization. This is of particular significance in the domestic indoor environment where the proteolytic activity of Der p I, the group I allergen of the house dust mite Dermatophagoides pteronyssinus, may influence the allergenicity of mites. Using class-specific proteinase inhibitors and active-site affinity chromatography, we have previously shown that Der p I exhibits a mixed cysteine-serine proteinase activity. Measurement of the amount of cleavage, however, did not determine whether the inhibitors used were targeting exactly the same proteolytic mechanism. Objective To resolve this issue, we have examined whether the cleavage specificity of the cysteine and serine proteinase activities of Der p I was the same. Methods HPLC and mass spectrometry were used to analyse and identify the products of a Der p I-digested peptide substrate and thus identify the peptide bonds cleaved. Results Der p I cleaves different peptide bonds, depending upon the class of proteolytic mechanism used. In the model peptide substrate insulin B chain, the cysteine and serine proteinase activities of Der p I showed preference for glutamic acid and arginine respectively in the P1 position. Conclusion These data suggest the existence of more than one mechanistic form of the allergen immunologically identified as Der p I. If proteolytic activity is indeed a function of allergenicity, this information may have important implications for the pathogenicity of Der p I and the ability of innate antiproteinase defences in the respiratory tract to prevent immune sensitization.     

Structural Studies of Immunoglobulins

In 1946, when I was starting work as research student under the supervision of Dr F. Sanger, the second edition of Karl Lansteiner's book" The Specificity of Serological Reactions'[I] reached England. In it was summarized the considerable body of information available on the range of antibody specificity and much of it was Landsteiner's own work or by others using his basic technique of preparing antibodies against haptenes and testing their ability to inhibit the precipitation of the antisera and t he conjugated protein. Also described in this book was the work in Uppsala of Tiselius and Pederson in collaboration with Heidelberger and Kabat in which they showed that all rabbit antibodies were in the y globulin fraction of serum proteins and that they had a molecular weight of 150.000. This combination of an apparently infinite range of antibody-combining specificity associated with what appeared to be a nearly homogeneous group of proteins astonished me and indeed still does.     

Flecainide

Flecainide. Flecainide is a Class IC antiarrhythmic agent whose primary electrophysiologic effect is a slowing of conduction in a wide range of cardiac tissues. It is well absorbed and effective in suppressing isolated premature ventricular contractions (PVCs) or nonsustained ventricular arrhythmia but has only a modest efficacy when electrophysiologic testing is used as an endpoint. Us adverse effect on mortality in the CAST trial suggested a propensity to proarrhythmia-a phenomenon to which the Class IC agents appear particularly prone. Despite the applicability of the CAST study only to patients with a prior myocardial infarction, there has been a shift away from flecainide in ventricular arrhythmia, but the low noncardiac side effect profile of the agent allows for its continued use in a wide variety of supraventricular arrhythmias. ( J Cardiovasc Electrophysiol, Vol. 5, pp. 964–981. November 1994 )     

DEFINING A STANDARD INTUBATING POSITION USING "ANGLE FINDER"

Study of patients who exhibit only limited morphological abnormalityyet present difficulty with direct laryngoscopy is facilitatedby a standard intubating position. The "Angle Finder" instrumentallows implementation of a simple reproducible geometric standardwhich is applied easily in formal research work and in clinicalpractice and teaching. The proposed standard relates to thecurved (Macintosh) laryngoscope blade and a supine patient.The lower neck flexion is 35° and extension of the planeof the face 15°, each angle measured relative to horizontal.Initially, the standard was derived from a review of the literature,then validated in a study of the intubating practices of 10senior anaesthetists. A more detailed study of 10 normal volunteersconfirmed reproducibility and, for nine patients with a historyof difficult direct laryngoscopy, the standard was shown tobe appropriate.     

The kinetics of metaphase arrest in human psoriatic epidermis: an examination of optimal experimental conditions for determining the birth rate

The optimum experimental conditions have been investigated for the measurement of the birth-rate in human psoriatic epidermis using the vinca alkaloids vinblastine and vincristine. The dose response characteristics of the two drugs were assessed over a 2.5 h collection period; although the dose response characteristics differed between the two agents, a dose of 1μg injected intradermally was considered to be optimal for both. The linearity of metaphase correction was assessed for both agents, taking biopsies for up to 10 h after injection. It was found that there was a delay period for up to an hour which must be avoided during the analysis to prevent an underestimate of the birth rate. However, linearity was then demonstrated for up to 4 h after injection. Metaphase degeneration was assessed by isolating a cohort of unlabelled cells in the G₂ phase and tracing their fate over the next 10 h. It was found that the minimum life of an arrested metaphase was of the order of 4 h, and then metaphases degenerated at the rate of approximately 0.4% per hour. It is recommended that metaphase arrest experiments in psoriatic epidermis be confined to 4 h although, if required, correction factors are available to correct for experiments which are lengthened. Finally it is shown that flux into DNA synthesis exceeds the flux into mitosis by four or five times; several explanations are considered, and it is thought that the most likely explanation involves the death of psoriatic cells in the G₂ phase.     

Epitheliomas in patients receiving razoxane therapy for psoriasis

We report two cases in which cutaneous squamous cell carcinomata developed in patients with psoriasis on razoxane therapy. The relevance of razoxane as well as past treatment for psoriasis in the aetiology of these tumours is discussed.     

Speed of injection and spread of bupivacaine in the epidural space

Speed of injection of bupivacaine was assessed in 73 women who received epidural analgesia in labour. Rapid injection was shown to produce quicker onset of epidural block and more reliable perineal anaesthesia than slow injection, but there was no difference in the final extent of the block.     

Independent folding of autolytic fragments of thermolysin and their domain-like properties

High molecular weight autolysis products from thermolysin have been isolated and identified. The primary fragments correspond to residues 1 to 187–204 (21kD) and residues 187–204 to 316 (12kD), respectively. The fragments are both capable of independent refolding upon removal of denaturant. On the basis of these results, we suggest that the first step in the unfolding pathway of thermolysin involves unfolding of an interdomain region and domain separation. Bound calcium ions at sites 1, 2 and 4 play a major role in protecting the protein against both autolysis and unfolding, probably by stabilizing the interdomain region and enhancing domain-domain interactions.