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In order to find a new reagent for the affinity labelling, 6-phosphogluconate dehydrogenase was treated with glyoxylate, a versatile metabolite with a carboxyl and a reactive aldehydic group. High concentrations of glyoxylate inhibit the enzyme, while in the presence of the reducing agent cyanoborohydride, the enzyme is irreversibly inactivated by only millimolar glyoxylate. This indicates the formation of a Schiff base between the aldehydic group of glyoxylate and one enzyme lysine residue. The kinetics and substrate competition suggest that inactivation is due to affinity labelling. In the first step the inhibitor carboxylic group binds to the substrate carboxyl binding site, and in the second slower step the aldehydic group binds a nearby lysine. We have also found that other enzymes are inactivated by the combined actions of glyoxylate and cyanoborohydride, with a saturation kinetics. Hence, glyoxylate can be helpful to identify specific lysines at the carboxyl binding sites in proteins.

When cultured in liquid media, samples of the yeast Trichosporon grow readily and degrade phenol; glutamate was found to stimulate both fungal growth and phenol catabolism, with a distinctive lag. In addition, this same strain grows in the presence of 2-chloro-phenol and 2-methyl, 4-chlorophenol (which are also degraded) and in the presence of 2-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol, which are either degraded or not, as in the case of 4-nitrophenol. The kinetics of both growth and of aromatic catabolism is suggestive of inductive phenomena for key metabolic enzymes.

Somatostatin (SRIF) inhibits calcitonin and T3-T4 secretion in thyroid. We have investigated the in vitro effect of SRIF on the basal and TSH induced [3H]thy incorporation, thyroglobulin (tgb) RNA and cAMP level in follicular cells, isolated from normal and adenomatous human thyroids. [3H]thy uptake has been evaluated as TCA-precipitable material in 2, 4, 8, 24 h incubated follicles and 24 h incubated adherent cells. Tgb RNA has been quantified with cytoplasmic dot blot hybridization and cAMP level with RIA method. SRIF reduces basal and TSH-induced [3H]thy in both suspension follicles and epithelial adherent cells. However it does not modify tgb RNA nor cAMP levels in incubated follicles. These data suggest a direct antiproliferative effect of SRIF on human thyroid.