Two palmitoyl-CoA synthetase activities have been demonstrated in rat liver microsomes. One, catalyzing palmitoyl-CoA synthesis from ATP, palmitate and CoASH as well as from palmitoyl-AMP and CoASH. A second enzyme reacts with the fist constituents only and is inactive with palmitoyl-AMP. The first enzyme, but not the second catalyzes the reaction between palmitoyl-AMP and PPi to yield ATP and palmitic acid.This duality has been shown by: (a) partial separation of the two types of activity by fractional solution in Triton X-100, (b) kinetic behaviour testing competition between both reaction mixtures at saturating concentrations and (c) the varying distribution of the two activities in microsomes obtained from rats under different dietary regimes or when diabetes was induced by alJoxan. When the enzyme was solubilized and purified [2], it showed very high activity in reaction (1) but was almost devoid of activity for reaction (2) and (3) [3]. The latter two reactions are generally considered to be part reactions of palmitoyl-CoA synthesis according to reaction (1). Their disappearance upon purification raised a number of possibilities: (a) That the loss of the part reactions was due to change in the enzyme protein during extraction and purification, making it non-accessible to palmitoyl-AMP. (b) That two enzymes coexist in liver microsomes ; one, which had been purified, catalyzes reaction (I), but not (2) and (3), while a second enzyme catalyzes all three reactions.Indications for the second possibility have been obtained in the experiments, to be presented, involving preparative separation of the two types of activities, mutual competition between the substra- +AMP (2)Enzyme. Palmitoyl-CoA synthetase, acid: CoA ligase-(AMP) (EC 6.2.1.3).tes and the changing distribution of these activities in intact microsomes obtained from livers of rats under differing conditions. and 100-4OOpg microsomal protein in a total volume of 0.6 ml. EDTA was added in order to avoid non-enzymatic CoASH disappearance which otherwise occurred in the presence of ATP. Incubation was carried on for 10 min a t 30 "C and the reaction was stopped by the addition of 0.2 ml 15O/, trichloroacetic MATERIALS AND METHODS Microsomes
The specific surface area of Recent sediments of Lake Kinneret was measured and the contributions of various sediment components to it were evaluated. Most of the lake sediments had specific surface areas larger than 100 m2 g−1. Average SSA of the sediments is 181.8 ± 59.7 m2 g−1, whereas that of the noncarbonate fraction, constituting on the average 54.8 ± 12.3% by weight of the sediment, is 374.6 ± 106.9 m2 g−1. Despite their high proportion in the sediment, carbonates contribute only a very small fraction of the specific surface area; clay minerals in the 0–2‐µ size fraction, particularly smectite, contribute most of it.
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