Electrostatic effects on the spectral and redox properties of Clostridium pasteurianum flavodoxin: effects of salt concentration and polylysine

When polylysine is complexed to flavodoxin at low ionic strength, the electrostatic potential of the region which is involved in electron transfer is modified such that positively charged oxidants react more slowly with flavodoxin semiquinone, and negatively charged oxidants react more rapidly. The reaction rate of the uncharged benzoquinone molecule is unaffected. An especially strong effect (approximately 200-fold) occurs with ferricyanide. This is interpreted in terms of electrostatic control of the reaction site. Complexation also changes the conformation of the region around the FMN prosthetic group, which is reflected in the fluorescence and circular dichroism spectra of the protein.     

In vitro stabilization of 6-methylsalicylic acid synthetase from Penicillium urticae

In continuing studies of patulin biosynthesis, the first enzyme of the pathway, 6-methylsalicylic acid synthetase, was found to be far more labile than were the later enzymes of the pathway. Attempts were made to stabilize 6-methylsalicylic acid synthetase in vitro. The combined addition of the cofactor NADPH, the substrates acetyl-CoA and malonyl-CoA, the reducing agent dithiothreitol, and the proteinase inhibitor phenylmethylsulfonyl fluoride to cell-free extracts was found to prolong the half-life of the enzyme as much as 12-fold. This suggested that proteolysis and the conformational integrity of the enzyme may play an important role in controlling the duration of antibiotic biosynthesis in vivo. This was in agreement with the finding that the intracellular proteinase content of antibiotic-producing cells of Penicillium urticae rapidly increased just before the loss of 6-methylsalicylic acid synthetase content. These in vitro stabilization studies have provided some insight into the metabolic conditions that may stabilize these enzymes in vivo, and into possible ways of extending the life of these catalysts.     

Effects of iodine deficiency on mental and psychomotor abilities

The allometric relationships between canine base area, first molar and summed molar crown area, and the glabella–opisthocranion distance, and the direct allometric relationships between canine and molar size have been established in five primate taxa. Separate sex and combined sex ‘intraspecific’, and ‘interspecific’ regression and ‘best fit’ allometry coefficients were computed. This analysis showed that for any increase in glabella–opisthocranion length, the rate of increase in canine size exceeds the rate of increase in molar area, and ‘best fit’ solutions indicate that canine base area is positively allometric when related directly to molar crown area. These results were compared with data available for the ‘gracile’ australopithecine, A. africanus, and two ‘robust’ australopithecine taxa, A. boisei and A. robustus. The differences in canine and molar size which occur between the ‘gracile’ taxon and the two ‘robust’ taxa do not correspond to any of the trends in the comparative allometric models. Data on glabella–opisthocranion length for the fossils, meagre though they are, show that while the proportional increase in molar crown area between the taxa corresponds to comparative allometry models, the reduced canine size in the ‘robust’ taxa is against comparative allometric trends. These results indicate that, at least in terms of canine/molar proportions, the differences between the ‘gracile’ and ‘robust’ australopithecines are not merely allometric and may indicate significant dietary or behavioural differences.     

EGF modulated Na+/K+ ATPase in cultured fibroblasts

The behaviour of Na+/K+ ATPase during cell growth has been studied. Human cultured fibroblasts were used in the presence or absence of EGF. Sample and control cultures were stopped by gathering and washing the cells with tris buffer. Homogenates were tested for Na+/K+ ATPase activity by the method of incubating and for the -SH groups content (Ellman). Na+/K+ ATPase activity that slightly increases in the controls is strongly reduced by the addition of EGF. The behaviour shows evidence for a double mechanism of action: I) involvement of the cAMP system 2) decrease of the -SH group availability.     

Purification of human cartilaginous proteoglycans and technical aspects of the radioimmunoassay

Proteoglycans (PG) have been purified by classical methods from human articular cartilage in order to set up a radioimmunoassay. Conditions of labelling, purification of labelled PG, and optimal conditions of buffer, temperature, duration of incubations and dilution of antiserum are described. Separation of free and bound PG is performed by immunoprecipitation. It is demonstrated that human articular PG can be assayed quantitatively by RIA procedure, with the sensitivity of +/- 2 femto-moles (+/- 5 ng) per tube.