9304029 Abeles (1) The decarboxylation of mevalonate pyrophosphate to isopentenyl pyrophosphate will be investigated as well as the basis of the inhibition by 5-flouro methyl mevalonate pyrophosphate. This enzyme catalyzed reaction is one step in cholesterol biosyntheses. Inhibition could lead to reduction of cholesterol synthesis. It is proposed that the transition state for the decarboxylation has a carbo-cationic character. To test this, the appropriate demethy- mevalonate pyrophosphate analogue will be prepared and subjected to enzyme action. If a carbo-cation transition state is involved the reaction should proceed slowly. In the event a methylphosphate addition occurs, analogues will be devised to block enzyme action. Hopefully, a more complete understanding of the mechanism will lead to effective inhibitors of the enzyme and control of cholesterol synthesis. (2) In all living organisms 5-S-methyl adenosine is converted to methionine. Four novel compounds, which are intermediates in the pathway, have been characterized, as well as four new enzymes. It is the goal of this research to identify all intermediates and all enzymes of the pathway. In this system a deadenylylated C5 intermediate, 1,2-dihydroxy-5-methylthio-1- pentene-3-one, is formed and spontaneously converts to a secondary intermediate on the way to methionine. It is likely that this reaction is enzyme catalyzed. After the complete pathway is identified, an inhibitor will be developed. This inhibitor will be used to evaluate the importance of the pathway in various microorganisms and in plant cells, where it may be essential for ethylene production. %%% Each living cell carries out hundreds of chemical interconversions. They are called metabolic pathways. The proper function of each pathway is essential for the survival of the cell. Blockage of a pathway can be fatal. This research program consists of two parts. (1) An enzyme of the metabolic pathway for the formation of choles terol will be studied. We hope that a complete understanding of the mechanism of action of the enzyme (mevalonate-pyrophosphate decarboxylase) will allow for the development of a compound to inhibit the enzyme and thereby control cholesterol formation in plant and animal cells. (2) All living organisms convert 5-S- methyl adenosine (MTA) to methionine, an essential amino acid. The intermediates of the pathway will be characterized, as well as the enzymes. With this information, it will be possible to develop an inhibitor to block the pathway and thereby determine its role in different microorganisms and in plants. In plants, it may operate to produce ethylene, a plant hormone, that controls ripening of fruit. Inhibition of the MTA in plants could be used to stop ethylene production, and serve agriculture as a useful means to control fruit maturation. Supported jointly by the Metabolic Biochemistry and Molecular Biochemistry Programs, Division of Molecular & Cellular Biosciences. ***
