Structural alterations of albumin, their dependence on concentration and the role of free -SH groups at thermal denaturation, as well as the reversibility of thermally induced structural changes, were studied. Application of various physical methods provides information on a series of structural parameters in a major concentration range. Apart from changes of the helix content, heat treatment gives rise to p structures which are amplified on cooling and which are correlated with the aggregation of albumin. With rising temperature and concentration the proportion of b structures and aggregates increases.At degrees of denaturation of up to 20';;; complete renaturation is possible in every case. The structure content is concentration-dependent even at room temperature. It may be that intermolecular interactions induce additional a-helix structures which are less stable, however, than the ones stabilized by intramolecular interactions. Unfolding of the pocket containing the free -SH group of cysteine-34 enables disulphide bridges to be formed leading to stable aggregates and irreversible structural alterations. Through binding of N-ethylmaleimide to free -SH groups, which blocks the formation of disulphide bridges, it is possible to prevent aggregation and irreversible conformational changes. At temperatures below 65 -70 "C, oligomers are formed mainly via intermolecular p structures.In the preparation of human serum albumin for clinical purposes its behaviour at different temperatures is of importance. The albumin is treated at 60 "C for about 10 h to inactivate the hepatitis virus. The structure should be largely retained of course in this treatment. Sodium octanoate or sodium octanoate + acetyltryptophan may be used as stabilizer. We distinguish in general two stages in the heat treatment of albumin. The first stage includes reversible structural alterations, the second one includes irreversible structural alterations, which may not necessarily result in a complete destruction of the ordered structure [l--31. Although a number of investigations are available on the problem of the thermal exposure of albumin, there are still open questions to be answered concerning in particular the nature of structural alterations, the limits of reversibility, the influence of concentration and environmental conditions and the molecular mechanism of the action of the stabilizers and their relative effectiveness under various conditions. Experiments perAbbreviations. H + 'H exchange, hydrogen -deuterium exchange; ESR, electron spin resonance; CD, circular dichroism; MalNEt, N-ethylmaleimide.formed on horse serum albumin by Zimmermann and Dittmar [4] showed that higher molecular weight components will be increasingly formed after heat treatment of 15 min at 100 "C. If the time of exposure is 60min or more, the aggregation products will decompose into low-molecular-weight fragments which are serologically inactive. They may still cause, however, severe shock reactions in anaphylaxia experiments. The authors suggest that species des...
Abstract. Bile acids and their sulphated and glucuronidated derivatives were studied in three children with persistent intrahepatic cholestasis, two children with intrahepatic biliary hypoplasia, and four healthy children. In children with cholestasis, biliary bile acids consisted of 11(±0–3) % 3 β‐hydroxy‐delta‐5‐cholenoic acid, 2‐1(± 0–6) % lithocholic acid, 2‐2(± 11) % deoxy‐cholic acid, 5–8(±2‐2) % ursodeoxycholic acid, 39‐1(± 1 ‐4) % chenodeoxycholic acid, 0–5(± 0 2) % hyo‐cholic acid, and 49‐3(± 3 0) % cholic acid. Of these bile acids 121 (±l 9) % were sulphated and 4–5 (±0 6) % were glucuronidated. In healthy children, biliary bile acids consisted of 0–7 (±0–4) % lithocholic acid, 3–4 (±0 8.) % deoxycholic acid, 0–1 (±0 1) % ursodeoxycholic acid, 32‐7 (±6 9) % chenodeoxycholic acid, and 631 (±7 1) % cholic acid. Of these bile acids, 0–6±0 1 % were sulphated and 0–2 ±0 1% were glucuronidated (mean ± SEM). In the urine of healthy children, 3‐3(±0 6) mg/24 h bile acids (1–5±0 3 mg sulphates and 0–1 ±0 1 mg glucuronides) were excreted, in the urine of children with cholestasis 61‐4 (± 10 2) mg/24 h (30 2 ±7 1 mg sulphates and 5 6 ±1 2 mg glucuronides) were excreted. Thus in children with cholestasis the amounts of sulphated and glucuronidated bile acids are greater than in healthy controls. Substantial amounts of sulphated and glucuronidated bile acids are excreted in bile and urine of these patients. Phenobarbitone treatment in the five children with cholestasis led to a reduction of serum bile acids from 90 4 (± 13 2) μg/ml to 39 3(±3 6) μ//ml, a relative increase of bile acid glucuronides in bile from 45 (±0 6)% to 8 l(±0 6)%, a slight alteration of the bile acid sulphates in bile from 121(±l 9) % to 111 (± 1 2)% and no alteration of the bile acid spectrum. Urinary excretion of bile acids decreased from 61 4 (± 10 2) mg/24 h to 34 7(±3 0) mg/24 h. Phenobarbitone treatment of children with cholestasis thus induced glucuronidation of bile acids but had no significant effect on sulphation or on formation of individual bile acids.
Circular dichroism measurements with DNA-spermine complexes at 0.075 M NaCl and at 0.15 M NaCl reveal'+4' (type I) and -W (type II) CD spectra respectively. From small-angle X-ray scattering studles it could be shown that type I has a long-range order, short-range order supramolecular structure, while type II is of long-range disorder, short-range disorder structure. The secondary structure of the DNA in both types of condensates is B-like as concluded from wide-angle X-ray scattering diagrams of the condensates and from a comparison with the wide-angle X-ray curves of DNA and RNA in solution.
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