Sucrose phosphate synthase (SPS) is a key enzyme in determining the biochemical capacity of leaves for sucrose synthesis. However, detailed knowledge of SPS at the biochemical and molecular genetic levels is lacking and must be obtained in order to understand the regulation of this pivotal enzyme. Study at the molecular level can be stated as a result of obtaining monoclonal antibodies against the spinach leaf enzyme (polyclonals are in preparation). Using the antibodies, direct evidence has been obtained for phosphorylation of SPS in vivo, and also a partial amino acid sequence has been determined from which and oligonucleotide probe will be made and used to isolate a cDNA. The proposed studies will expand on these developments and examine the two subtypes of coarse control which regulate SPS activity in vivo: covalent modification mechanism; and 3) produce a DNA probe to the enzyme with which to begin studies of transcriptional/translational mechanisms that regulate the expression of the SPS gene. This project investigates the enzymes which determines how much sucrose is made in leaves of plants, and thereby how much plant growth is possible. This has been a very elusive enzyme but recent success in raising a monoclonal antibody now opens the door to a through study now opens the door to a through study of this critically important enzyme.***//
