The Prothrombin Activator of Echis Carinatus Venom:Characterization and Mode of Action

The venom of the saw scaled viper, Echis carinatus, contains a protein capable of convertis prothrombin to thrombin. This prothrombin activator (ECA) has been purified 45-fold by affinity chromatography on wheat germ agglutinin followed by ion exchange chromatography on DEAE-Sephacil. ECA was homogeneous as assessed by dodecyl sulfate poly acrylamide gel electrophoresis (SDS-PACE). Sialic acid, neutral sugars, and hexosamines were present at 4.2, 7.2 and 5.8 w/wX respectively. Amino acid analysis of reduced and carboxymethylated ECA revealed an unusually high cysteine content of 9 moles %. ECA is inhibited by chelators such as EDTA and o-phenthroline, but is active after treatment with chelex. However, atomic absorption studies revealed that neither Ca, Co, Cr, Cu, FeMηnor घη is present at more than 0.01 moles/mole of active protein after chelex treatment. Arrhenlus plots of the temperature dependence of thrombin formation give a similar activation energy and T½ as Arrhenlus plots of data obtained for a temperature induced conformational change in prothrombin. These data suggest that the activation of prothrombin by ECA requires a particular conformational Isomer of prothrombin as well as a group on ECA which can interact with metal chelators.(Supported, in part, by NIH Grant HL 19282)

Kinetic studies on the activation of human factor X. The role of metal ions on the reaction catalyzed by the venom coagulant protein of Viper russelli

The effect of Ca2+, Mg2+, and Mn2+ on the initial rate of activation of human Factor X by the venom coagulant protein of Vipera russelli has been investigated. Neither Mg2+ nor Mn2+ alone support the reaction. Ca2+ is an essential activator and exhibits cooperative kinetics. Both Mg2+ and Mn2+ enhance the reaction cooperatively when Ca2+ is present at suboptimal concentrations. Similarly, Ca2+ quenches the intrinsic fluorescence of human Factor X in a cooperative manner. While neither Mg2+ nor Mn2+ by themselves affect the fluorescence of human Factor X, they decrease the cooperativity of the Ca2+ binding to the protein as judged by Hill plots of the Ca2+ -induced fluoresence quenching. EPR measurements indicate that there are three high affinity Mn2+ binding sites on human Factor X which can also bind Ca2+. Positive cooperativity was not observed for Mn2+ binding. These data indicate that Ca2+ can cause a conformational change of the Factor X molecule which allows the activation reaction to proceed. We propose that Mn2+ does not support the activation of human Factor X because it cannot induce a necessary conformational change in the absence of Ca2+.

Assessing changes of hospital admission in preschool children. Critical evaluation

In discussing social class differentials in childhood mortality and morbidity a recent report on the British child health services suggests that it is possible to identify children at risk, and a government publication has indicated that health visitors (community nurses) could do this. The National Survey of Health and Development, a longitudinal study of over 5000 children regularly investigated from birth so far to age 31 years, gives an opportunity to test the usefulness of these propositions, since it has complete illness records of the study population and health visitors' assessments of their home circumstances, maternal care, and use of child welfare services. This study shows that these assessments were not particularly successful in identifying children at risk of hospital admissions for certain illnesses, even when more than one hospital admission or a serious illness later occurred. The maximum reduction of hospital costs by such identification would be little better than one-third and there would be an unquantifiable, but very real, stress imposed on families in which children were wrongly identified as at risk. It is suggested that further development of health visitors' work as family nurses would give a more effective form of child health care by providing greater sensitivity of surveillance, by involving parents in preventive care, and by making appropriate use of health visitors' skills.

Purification and structural analysis of the fourth component of human complement

The fourth component of human complement (C4) has been purified in 20% yield from fresh plasma using as starting material the 5-12% poly(ethylene glycol) precipitate which had been depleted of plasminogen by an affinity adsorbent. Sequential ion-exchange chromatography on diethylaminoethylcellulose, QAE-Sephadex, and DEAE-Bio-Gel A resulted in C4 homogeneous by immunological criteria and by polyacrylamide gel electrophoresis, the last chromatographic step achieving separation of native from inactivated C4. Reduction with 20 mM dithiothreitol for 2 h at 37 degrees C in 0.25 M 2-amino-2-hydroxymethyl-1,3-propanediol hydrochloride, pH 8.6, effected cleavage of the interchain disulfide bonds. A three-chain structure for C4 was confirmed, and molecular weight estimates of 93 000 +/- 9300, 75 000 +/- 7500, and 30 000 +/- 3000 determined for the alpha, beta, and gamma chains, respectively. The effects of known inactivators of C4 upon the chains of C4 were investigated, confirming that the inactivations by C1s and trypsin were accompanied by the fragmentation of the alpha chain. Inactivation of C4 by hydrazine, on the other hand, produced no detectable change in chain size. Separation of the chains was accomplished by gel filtration in the presence of 1 M acetic acid. Amino acid compositions of native C4 and the constitutive chains have been performed, and N-terminal sequences of the latter established by automated Edman degradation.

Stuttering, speech rate, and the metronome effect

Methodological inadequacies cast doubt on previous investigations of the hypothesis that metronome-paced speech reduces stuttering by slowing the rate of speech. In the present study, 6 stutterers' fluent speech rates were calculated by excluding the time occupied by stutters and pauses. The fluency-enhancing effect of metronome pacing was independent of speech rate.

A labour of love

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Steroid synthesis in a human virilising adrenal carcinoma - some unusual features

A patient presenting at the Universitäts-Frauenklinik, Berlin with a long history of increasing hirsutism and virilism provided an opportunity to study an unusual form of adrenal hyperfunction. It was found that she behaved abnormally with respect to the dexamethasone suppression test since her highly elevated 17-oxosteroid output further increased by approximately 400% with 8 mg/day dosage. Her basal 17-hydroxycorticosteroid output was elevated but not grossly so, nor did she exhibit the usual signs of Cushing's syndrome of weight increase and florid complexion.

At operation a »tennis ball« size adrenal carcinoma was removed from the left side. Incubation studies were performed on sliced tumour tissue with substrates [1-14C] acetate, [7α-3H] pregnenolone, [4-14C] progesterone and [4-14C] androst-4-ene-3,17-dione. The frozen incubation mixtures were subsequently flown to Cardiff for steroid analysis by reverse radioisotope dilution techniques.

The combined urinary and incubation results suggested that, in vivo, the tumour secreted DHA and not DHA sulphate and that there appeared to be a considerable deficiency of DHA-3β-hydroxysteroid dehydrogenase/Δ5−4-isomerase and of DHA-3β-sulphokinase activities although the steroid-11β-hydroxylase, 17α-hydroxylase and 21-hydroxylase activities seemed unimpaired.

The story of a 'little black bag'

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