Homology model of thyroxine binding globulin and elucidation of the thyroid hormone binding site.

The tertiary structure of thyroxine binding globulin (TBG) has been modelled on the basis of its close homology to alpha 1-antitrypsin, the archetype of the serine protease inhibitor (serpin) superfamily. Energy minimization was applied to the model to refine the structure further. The putative thyroid hormone binding region suggested in previous labelling studies was found to exist within a beta-barrel structure of complementary dimensions to the thyroid hormones. The model also revealed that the binding cleft provides the hydrophobic environment and specific ionic interaction sites deemed important for thyroid hormone binding. The model is in good agreement with evidence derived from previously reported T3 and T4 binding, stability and isoelectric focussing studies of TBG and TBG variants. Finally, T4 analogue and drug binding studies have enabled us to postulate the orientation and manner of hormone binding to TBG. This may prove to be of assistance in the development of potent and specific, non-thyroidal ligands and also aid in the understanding of physiological thyroid hormone binding interactions.     

Sex difference in distribution and iron responsiveness of the two ferritins of rat cardiac and skeletal muscle

The presence of two electrophoretically and structurally distinguishable forms of ferritin (“fast” and “slow”) in cardiac and skeletal muscle (diaphragm) of the rat was confirmed. Although the total amount of cardiac ferritin showed no difference in concentration in male and female rats, the distribution between the fast and slow species was remarkedly different in the two sexes, the fast form predominating in the cardiac muscle and diaphragm of the female. In agreement with this, the rates of synthesis and of degradation of the fast species were greater in teh female, while the opposite obtained for the male. Iron administration stimulated synthesis of each ferritin species in the cardiac muscle and diaphragm of both sexes. Induction of cardiac connective tissue hypertrophy with isoproterenol inverted the ratio of slow to fast ferritin in female rats, while iron adminsitration along with isoproterenol restored this to normal. It is concluded that the metabolism of ferritin in cardiac and skeletal muscle is sensitive both to sexual status and to iron administration.     

The self-retained Le Fort I osteotomy

Because inferior repositioning of the maxilla after Le Fort I osteotomy has a high relapse rate, a modified bone cut oriented obliquely upward has been tried in 29 patients. The modification allows extrusion of the fragment while maintaining good bony contact, thus eliminating the need for bone grafts. It also permits self-retention of the fragment and can be adapted to movements in any plane.     

Identification of major common extracellular proteins secreted by Aeromonas salmonicida strains isolated from diseased fish

Ten different strains of Aeromonas salmonicida that were isolated from diseased fish were grown under identical conditions (24 h at 25 degree C) in 3% (wt/vol) tryptone soya broth medium supplemented with vitamins and inorganic ions. In each case the extracellular proteins that were formed were compared by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and it was found that there were two significant common components, one with a molecular weight of 70,000 and the other with a weight of 56,000. Application of enzyme purification techniques to the supernatant fraction proteins of a culture of one of the strains resulted in the isolation of a 70-kilodalton (kDa) component, which was found to be a serine protease, and a 56-kDa component, which was hemolytic to trout erythrocytes. Rocket immunoelectrophoresis with rabbit antibodies to the isolated protease and hemolysin showed the same antigenic components in the supernatant fractions of all the cultures. These activities were assayed, and protease activity was found to vary by a factor of three, from 59 to 195 U/ml, while the range of hemolytic activity was over a narrow band, from 28 to 43 U/ml. There was an inconsistency between the immunoelectrophoretic and direct assay data in only one case. This indicated the presence of additional hemolytic activity, in addition to the 56-kDa component. The detection of large amounts of the same protease and hemolysin, two potent degradative activities, in a random series of strains of A. salmonicida suggests that they may be obligatory virulence factors in the development of furunculosis.