Vitamin A acetate is hydrolysed by highly purified carboxylesterases (EC 3.1.1.1) from liver and kidney of several species (pig, ox, man), whereas long-chain fatty acid esters of vitamin A are not split. [7,8]. The substrate specifity of these carboxylesterases is remarkably low. Observations of Frimmer and Gries [9] gave first indications that vitamin A acetatc is hydrolysed by pig liver esterase. In the present communication this reaction has been characterized in more detail by experiments on the enzymatic hydrolysis of vitamin A acetate in vitro by highly purified carboxyl-esterases of different origin. MATERIALS AND METHODS MaterialAll organic solvents not designated as analytical grade were distilled prior to use. All other reagents were of analytical grade.Vitamin A stearate and -oleate were kindly supplied by Prof. Dr. 0. Wiss, Hoffman la Roche, Basel/Switzerland. Nicrosomes and EnzymesPig liver microsomes a,nd carboxylesterases from pig liver, pig kidney and ox liver were isolated according to methods reporhed previously [3,5,6]. The analogous enzyme from human liver is purified a t present in our laboratory [lo].Determinations o/ Enzyme Activity For assaying the activity of the various carboxyesterase preparations, acetanilide [3,5] and p-nitrophenylacetate [Ill were used as substrates. ProteinProtein was determined by a biuret method [12); in the case of microsomes a turbidity correction was made by addition of KCN [13]. Substrate SolutionsVitamin A Acetate (10 m M ) . 16.43 mg crystalline vitamin A acetate + 5.5 mg hydroquinone were dissolved by slight warming in 1 ml of methanol and diluted to 5 ml with 0.1 M Tris-C1, pH 8

Cell free preparations of Tetrahymena thermophila contain an enzyme that catalyzes the direct desaturation of stearoyl CoA to octadecenoic acid. The enzyme is associated with the microsomal fraction of the ciliate. Substrate of the enzyme consists of either free stearic acid or stearoyl CoA. Both ATP and CoA are required when free stearate is the substrate and are also highly stimulatory when stearoyl CoA is the substrate. With stearoyl CoA as the substrate, either NADH or NADPH are required for desaturase activity. In presence of ATP and CoA, either NAD or NADP can replace NADH and NADPH. Desaturase activity is optimal when the enzyme is incubated at pH of 7.2 and a temperature of 30-35 degrees C. Highest levels of the stearoyl CoA desaturase are found in stationary phase ciliates grown at 35 degrees C.

A spin-Hall nano-oscillator (SHNO) is a type of spintronic oscillator that shows promising performance as a nanoscale microwave source and for neuromorphic computing applications. Within such nanodevices, a non-ferromagnetic layer in the presence of an external magnetic field and a DC bias current generates an oscillating microwave voltage. For developing optimal nano-oscillators, accurate simulations of the device's complex behaviour are required before fabrication. This work simulates the key behaviour of a nanoconstriction SHNO as the applied DC bias current is varied. The current density and Oersted field of the device have been presented, the magnetisation oscillations have been clearly visualised in three dimensions and the spatial distribution of the active mode determined. These simulations allow designers a greater understanding and characterisation of the device's behaviour while also providing a means of comparison when experimental results are generated.