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1. 1. The incubation of human fresh circulating lymphocytes with insulin leads to modifications in the behaviour of the pyruvate dehydrogenase complex (PDH) when the contact medium is supplemented with 50 μM Ca 2+ and Mg 2+ 2. 2. To investigate the mechanism involved in the PDH responsiveness to insulin in circulating lymphocytes and the role of Ca 2+ and Mg 2+ in this process, the PDH activity was assayed in lymphocytes combined with insulin and/or a number of substances whose mechanism of action is partially known. 3. 3. Of these some have been seen to mimick insulin effects on PDH, whereas other were tested for the first time in this study.

1. I. Trehalose synthase and trehalase behaviour has been analysed in cultured yeast cells isolated from baker's yeast to increase the understanding of the mechanisms involved in trehalose content modifications observed in anyhydrobiois and hydrobiosis. 2. 2. After desiccating yeast cells to a constant weight, trehalose levels sharply increased, whereas the glycogen content decreased, trehalose synthase was stimulated and trehalase was significantly inhibited. 3. 3. In desiccated cells after a rehydration for 15 min, trehalose levels dropped, the glycogen content further decreased, the activity of trehalose synthase declined while that of trehalase was dramatically stimulated. 4. 4. After rehydration for 12hr, while the trehalose and glycogen content decreased even more, the behaviour of the two enzymes was completely reversed, trehalose synthase being activated and trehalase inhibited. 5. 5. The reasons for such impressive enzyme activity alterations in desiccated and rehydrated cells for the moment remain unknown.

1. 1. The results of this study indicates that the binding of insulin to brain plasma membranes activates a membrane protease which, by a trypsin like mechanism, produces a soluble factor that modulates the PDH behaviour when added to brain mitochondria. 2. 2. The supernatant from brain plasma membranes incubated with 0.5 mg/ml trypsin added to mitochondria increases PDH activity levels and cancels PDH inhibition by NaF, as has already been seen when the plasma membranes are incubated with 25 μ U/ml insulin. No such effects are obtained when the incubation is run out with 0.5 mg/ml chymotrypsin. 3. 3. The supernatants from insulin or trypsin treated plasma membranes retain their activating properties on mitochondrial PDH also after dansylation; from these preparations a dansylated active on PDH material was separated by monodimensional chromatography on HPTLC silica Gel plates, using chloroform/1-butanol (93:7 v/v) as a solvent. 4. 4. Insulin incubation of plasma membranes pretreated with protease inhibitors (leupeptin, phenylmethylsulfonylfluoride) or with exogenous trypsin, but not chymotrypsin substrates (esters of arginine and tyrosine) yields an inactive supernatant on PDH. 5. 5. Insulin treated plasma membrane supernatants lose all stimulating properties on PDH after incubation for 1 hr with 2 mg/ml trypsin or chymotrypsin.