Lynen

Animals accumulate cholesterol from then diet but are also able to biosynthesize It from acetate The pioneering work that identified the key intermediates m the com plicated pathway of cholesterol biosynthesis was carried out by Konrad Bloch (Harvard) and Feodor Lynen (Munich) corecipients of the 1964 Nobel Prize for physiology or... 

Konrad E. Bloch, Feodor Lynen medicine, physiology discoveries concerning mechanism and regulation of cholesterol and fatty acid metabohsm... 

In 1953, Bloch, together with the eminent organic chemist R. B. Woodward, proposed a new scheme (see figure, part b) for the cyclization of squalene. (Together with Fyodor Lynen, Bloch received the Nobel Prize in medicine or physiology in 1964 for his work.) The picture was nearly complete, but one crucial question remained How could isoprene be the intermediate in the... 

Oxidation of higher fatty acids was first studied in 1904 by Knoop who fed animals with phenyl-substituted fatty acids and analyzed the products in the urine. He showed that the fatty acid oxidation results in the successive cleavage of two carbon moieties from the carboxyl end. Knoop coined the fatty acid oxidation mechanism as n-oxidation. As has been established by Kennedy and Lehninger in 1948-1949, oxidation of fatty acids occurs in the mitochondria only. Lynen and coworkers... 

The oxidation of fatty acids within the Knoop-Lynen cycle occurs in the matrix. The Knoop-Lynen cycle includes four enzymes that act successively on acetyl-CoA. These are acyl-CoA dehydrogenase (FAD-dependent enzyme), enoyl-CoA hydratase, 3-hydroxyacyl-CoA dehydrogenase (NAD-dependent enzyme), and acetyl-CoA acyltrans-ferase. Each turn, or revolution, of the fatty acid spiral produces... 

In the organism tissues, fatty acids are continually renewed in order to provide not only for the energy requirements, but also for the synthesis of multicomponent lipids (triacylglycerides, phospholipids, etc.). In the organism cells, fatty acids are resynthetized from simpler compounds through the aid of a supramolecular multienzyme complex referred to as fatty acid synthetase. At the Lynen laboratory, this synthetase was first isolated from yeast and then from the liver of birds and mammals. Since in mammals palmitic acid in this process is a major product, this multienzyme complex is also called palmitate synthetase. 

L10. Lynen, F., Participation of acyl-CoA in carbon chain biosynthesis. J. Cellular Comp. Physiol. 54, 33-49 (1959). 

The active form of acetate, acetyl CoA, was finally isolated by Lynen and Reichert in 1951 following studies of fatty acid oxidation (Chapter... 

In 1942, Lynen found acetate oxidation in starved yeast required the addition of energy which could be provided from the oxidation of... 

The actual pathway by which fatty acid oxidation occurred was established by Lynen (1952-1953). Its unique and characteristic reaction was the thioclastic attack by coenzyme A on the B-ketoacyl CoA derivative, splitting off the 2C fragment, acetyl CoA. Free coenzyme A was very difficult to isolate and although it was synthesized in Todd s laboratory in Cambridge in the mid-1950s, much of the early work from Lynen s laboratory utilized A-acetyl cysteamine as a not very efficient (ca.1%) coenzyme A analogue. It carried the essential thiol group of the B-mercaptoethylamine end of CoA and could be used in most, but not all, of the steps in the spiral. 

Lynen had studied chemistry in Munich under Wieland his skill as a chemist led to the successful synthesis of a number of fatty acyl CoA derivatives which proved to be substrates in the catabolic pathway. Many of these C=0 or C=C compounds had characteristic UV absorption spectra so that enzyme reactions utilizing them could be followed spectrophotometrically. This technique was also used to identify and monitor the flavoprotein and pyridine nucleotide-dependent steps. Independent evidence for the pathway was provided by Barker, Stadtman and their colleagues using Clostridium kluyveri. Once the outline of the degradation had been proposed the individual steps of the reactions were analyzed very rapidly by Lynen, Green, and Ochoa s groups using in the main acetone-dried powders from mitochondria, which, when extracted with dilute salt solutions, contained all the enzymes of the fatty acid oxidation system. 

Numerous experiments were then performed with mitochondria incubated with acetate, CoA, ATP, etc., in attempts to detect fatty acid synthesis. In 1957, Lynen and his colleagues reported the presence in mitochondria of a system which catalyzed the elongation of caproyl CoA to octanoyl CoA by the addition of an acetate unit. NADH and NADPH had to be present. The existence of this mitochondrial system was confirmed by Wakil et al. in 1961 who showed the 12C acid could be extended to 16C by successive additions of 2C fragments. 

The way biotin participates in carbon dioxide fixation was established in the early 1960s. In 1961 Kaziro and Ochoa using propionyl CoA carboxylase provided evidence for 14C02 binding in an enzyme-biotin complex. With excess propionyl CoA the 14C label moved into a stable position in methyl malonyl CoA. In the same year Lynen found biotin itself could act as a C02 acceptor in a fixation reaction catalyzed by B-methylcrotonyl CoA carboxylase. The labile C02 adduct was stabilized by esterification with diazomethane and the dimethyl ester shown to be identical with the chemically synthesized molecule. X-ray analysis of the bis-p-bromanilide confirmed the carbon dioxide had been incorporated into the N opposite to the point of attachment of the side chain. Proteolytic digestion and the isolation of biocytin established the biotin was bound to the e-NH2 of lysine. 

By 1960 it was clear that acetyl CoA provided its two carbon atoms to the to and co—1 positions of palmitate. All the other carbon atoms entered via malonyl CoA (Wakil and Ganguly, 1959 Brady et al. 1960). It was also known that 3H-NADPH donated tritium to palmitate. It had been shown too that fatty acid synthesis was very susceptible to inhibition by p-hydroxy mercuribenzoate, TV-ethyl maleimide, and other thiol reagents. If the system was pre-incubated with acetyl CoA, considerable protection was afforded against the mercuribenzoate. In 1961 Lynen and Tada suggested tightly bound acyl-S-enzyme complexes were intermediates in fatty acid synthesis in the yeast system. The malonyl-S-enzyme complex condensed with acyl CoA and the B-keto-product reduced by NADPH, dehydrated, and reduced again to yield the (acyl+2C)-S-enzyme complex. Lynen and Tada thought the reactions were catalyzed by a multifunctional enzyme system. 

Lynen s work on the breakdown and synthesis of fatty acids was recognized by the award of a Nobel prize in 1964. 

Boyer PD (1972) The enzyme, vol 6. Academic Press, New York, pp 37-115 Wood HG, Lochmuller H, Riepertinger C, Lynen F (1963) Biochem Z 337 247 Kawasaki T, Watanabe M, Ohta H (1995) Bull Chem Soc Jpn 68 2017 Segel IH (1975) Biochemical calculations, John WUey Sons, NewYork,p235 Kawasaki T, Fujioka Y, Saito K, Ohta H (1996) Chem Lett 195... 

Institut fiir Biochemie der LMU Miinchen, Feodor-Lynen-Str. 25, D-81377 Munchen, Germany. E-mail Famulok lmb.uni-muenchen.de... 

At high concentrations of acetyl-CoA in the liver mitochondria, two molecules condense to form acetoacetyl CoA [1]. The transfer of another acetyl group [2] gives rise to 3-hydroxy-3-methylglutaryl-CoA (HMC CoA), which after release of acetyl CoA [3] yields free acetoacetate (Lynen cycle). Acetoacetate can be converted to 3-hydroxybutyrate by reduction [4], or can pass into acetone by nonenzymatic decarboxylation [5]. These three compounds are together referred to as "ketone bodies," although in fact 3-hydroxy-butyrate is not actually a ketone. As reaction [3] releases an ion, metabolic acidosis can occur as a result of increased ketone body synthesis (see p. 288). 

F Lynen, Y Zhao, C Becu, F Borremans, P Sandra. Considerations concerning interaction characterization of oligopeptide mixtures with vancomycin using affinity capillary electrophoresis-electrospray mass spectrometry. Electrophoresis 20 2462-2474, 1999. 

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