ABSTRACT
In several experimental techniques D2O rather then H2O is often used as a solvent for proteins. Concerning the influence of the solvent on the stability of the proteins, contradicting results have been reported in literature. In this paper the influence of H2O-D2O solvent substitution on the stability of globular protein structure is determined in a systematic way. The differential scanning calorimetry technique is applied to allow for a thermodynamic analysis of two types of globular proteins: hen's egg lysozyme (LSZ) with relatively strong internal cohesion ("hard" globular protein) and bovine serum albumin (BSA), which is known for its conformational adaptability ("soft" globular protein). Both proteins tend to be more stable in D2O compared to H2O. We explain the increase of protein stability in D2O by the observation that D2O is a poorer solvent for nonpolar amino acids than H2O, implying that the hydrophobic effect is larger in D2O. In case of BSA the transitions between different isomeric forms, at low pH values the Nm and F forms, and at higher pH values Nm and B, were observed by the presence of a supplementary peak in the DSC thermogram. It appears that the pH-range for which the Nm form is the preferred one is wider in D2O than in H2O.
Subject(s)
Deuterium/chemistry , Muramidase/chemistry , Muramidase/metabolism , Protein Folding , Serum Albumin, Bovine/chemistry , Serum Albumin, Bovine/metabolism , Water/chemistry , Animals , Calorimetry, Differential Scanning , Cattle , Chickens , Deuterium Exchange Measurement , Protein Denaturation , Temperature , ThermodynamicsABSTRACT
AIMS: To examine the reliability of membrane cultures as a model solid-state fermentation (SSF) system. METHODS AND RESULTS: In overcultures of Aspergillus oryzae on sterilized wheat flour discs overlaid with a polycarbonate membrane, we demonstrated that the presence of membrane filters reduced the maximum respiration rate (up to 50%), and biomass and alpha-amylase production. We also show that the advantage of membrane cultures, i.e. total recovery of biomass, is not very evident for the system used, while the changes in metabolism and kinetics are serious drawbacks. CONCLUSIONS: The use of membrane cultures is artificial and without substantial benefits and therefore has to be carefully considered. SIGNIFICANCE AND IMPACT OF THE STUDY: In future studies on kinetics and stoichiometry of SSF, one should not completely rely on experiments using membrane cultures as a model SSF system.
Subject(s)
Aspergillus oryzae/growth & development , Aspergillus oryzae/metabolism , Bioreactors , Micropore Filters , Biomass , Fermentation , Industrial Microbiology , Kinetics , Oxygen Consumption , Polymers , Triticum/metabolism , alpha-Amylases/analysisABSTRACT
A case is described in which a large tumour was detected in the posterior mediastinum on a routine chest X-ray. Although the parathormone level was very high, no clinical nor radiographic signs of hyperparathyroidism were present. The tumour was removed by lateral thoracotomy and proved to be a parathyroid adenoma. Postoperatively the serum calcium returned to a normal level.
