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Query: UMLS:C0038187 (starvation)
 24,951 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Two secreted acid phosphatases (SAP1 and SAP2) were markedly up-regulated during Pi-starvation of tomato suspension cells. SAP1 and SAP2 were resolved during cation-exchange FPLC of culture media proteins from 8-day-old Pi-starved cells, and purified to homogeneity and final p-nitrophenylphosphate hydrolyzing specific activities of 246 and 940 micro mol Pi produced.min-1 mg.protein-1, respectively. SDS/PAGE, periodic acid-Schiff staining and analytical gel filtration demonstrated that SAP1 and SAP2, respectively, exist as 84 and 57 kDa glycosylated monomers. SAP1 and SAP2 are purple acid phosphatases (PAPs) as they displayed an absorption maximum at 518 and 538 nm, respectively, and were not inhibited by l-tartrate. The respective sequence of a SAP1 and SAP2 tryptic peptide was very similar to a portion of the deduced sequence of several putative Arabidopsis thaliana PAPs. CNBr peptide mapping indicated that SAP1 and SAP2 are structurally distinct. Both isozymes displayed a pH optimum of approximately pH 5.3 and were heat stable. Although they exhibited wide substrate specificities, the Vmax of SAP2 with various phosphate-esters was significantly greater than that of SAP1. SAP1 and SAP2 were activated by up to 80% by 5 mm Mg2+, and demonstrated potent competitive inhibition by molybdate, but mixed and competitive inhibition by Pi, respectively. Interestingly, both SAPs exhibited significant peroxidase activity, which was optimal at approximately pH 8.4 and insensitive to Mg2+ or molybdate. This suggests that SAP1 and SAP2 may be multifunctional proteins that operate: (a) PAPs that scavenge Pi from extracellular phosphate-esters during Pi deprivation, or (b) alkaline peroxidases that participate in the production of extracellular reactive oxygen species during the oxidative burst associated with the defense response of plants to pathogen infection.
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PMID:Purification and characterization of two secreted purple acid phosphatase isozymes from phosphate-starved tomato (Lycopersicon esculentum) cell cultures. 1247 24

This study compares the influence of phosphate (Pi) deprivation on the coordinate synthesis of the principle Pi-starvation inducible (PSI) acid phosphatase (AP) isozymes in a suspension cell culture with the homologous in planta system. Tomato suspension cells express three PSI purple AP isozymes: a heterodimeric intracellular AP (IAP) composed of 63 and 57 kDa subunits, and two monomeric secreted APs (SAPs) (84 kDa SAP1 and 57 kDa SAP2) localized in the culture media. Immunoblots probed with rabbit antibodies raised against purified SAP1 or IAP indicated the immunological distinctiveness of SAP1 relative to IAP and SAP2. Time-course studies of cells and seedlings undergoing a transition from Pi sufficiency to Pi deficiency revealed a close relationship between total IAP or SAP activity and relative amounts of antigenic IAP or SAP polypeptides. Upregulation of the pre-existing IAP in 6-day-old Pi-deficient (-Pi) suspension cells coincided with a 20-fold reduction in intracellular free Pi levels, which occurred 2 d prior to initial accumulation of SAP1 and SAP2 in the culture media. Similarly, root-specific SAP synthesis in -Pi seedlings occurred at least 7 d following IAP induction in roots or shoots. Preferential sequestration of limiting Pi to the leaves of the -Pi seedlings was suggested by the delayed induction of leaf versus root IAP. Our results confirm recent transcript profiling studies suggesting that PSI proteins are subject to both temporal and tissue-specific syntheses in- Pi plants.
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PMID:Differential synthesis of phosphate-starvation inducible purple acid phosphatase isozymes in tomato (Lycopersicon esculentum) suspension cells and seedlings. 1708 Jun 45