Partial purification and characterization of mRNAs encoding glycollate oxidase and catalase

Malate dehydrogenase isoenzymes: cellular locations and role in the flow of metabolites between the cytoplasm and cell organelles

Malate dehydrogenases belong to the most active enzymes in glyoxysomes, mitochondria, peroxisomes, chloroplasts and the cytosol. In this review, the properties and the role of the isoenzymes in different compartments of the cell are compared, with emphasis on molecular biological aspects. Structure and function of malate dehydrogenase isoenzymes from plants, mammalian cells and ascomycetes (yeast, Neurospora) are considered. Significant information on evolutionary aspects and characterisation of functional domains of the enzymes emanates from bacterial malate and lactate dehydrogenases modified by protein engineering. The review endeavours to give up-to-date information on the biogenesis and intracellular targeting of malate dehydrogenase isoenzymes as well as enzymes cooperating with them in the flow of metabolites of a given pathway and organelle.

Biogenesis of catalase in glyoxysomes and leaf-type peroxisomes of sunflower cotyledons

Eight charge isoforms of catalase (EC 1.11.1.6.) appeared in the peroxisomes of sunflower cotyledons during growth after germination (2.5 days of dark, continuous light thereafter). In the light, when glyoxysomes were transformed to leaf-type peroxisomes, the five more-basic forms (CAT 1 through CAT 5) became more prominent, while amounts of the three more-acidic forms (CAT 6 through CAT 8) decreased considerably. The isoforms CAT 1 through CAT 5 were hybrids of 55- and 59-kDa subunits, whereas CAT 6 through CAT 8 contained 55-kDa subunits exclusively. The catalase translation products changed during the transition of glyoxysomes to leaf-type peroxisomes. Polyadenylated RNA from 2-day-old cotyledons directed synthesis of 56-kDa subunits, whereas 59-kDa subunits predominated after in vitro translation of RNA from 4-day-old cotyledons. Both translation products were processed to lower molecular weight forms in vivo. The 56-kDa translation products were precursors for 55-kDa subunits in glyoxysomes. It could not be decided however, whether the 59-kDa precursors were processed to 56-kDa or 55-kDa subunits, because both subunits of lower molecular weight were present in leaf-type peroxisomes. Some of the 59-kDa precursors escaped proteolytic processing and formed hybrid isoforms (CAT 1 through CAT 5) with mature 55-kDa subunits. This type of isoform formation, i.e., condensation of mature and unprocessed subunits, has not yet been described for other plant catalases. In summary, the results showed that the postgerminative changes in the number and abundance of catalase isoforms resulted from changes in translation (transcription) of catalase precursors and assembly of proteolytically processed and unprocessed subunits into tetramers within peroxisomes acquiring leaf peroxisomal function.

Control of gene expression during induction of cultured peanut cells: mRNA levels, protein synthesis and enzyme activity of stilbene synthase

Stilbene synthase is an inducible enzyme occurring in a small number of plants. The enzyme is amenable to analysis and biochemical studies only after the cells are subjected to induction. Cell suspension cultures of peanut react very selectively if elicited with biotic inducers. Just as intact peanut plants produce stilbene phytoalexins when attacked by fungi so also do sterile cultured cells when treated with sterilized insoluble fungal cell walls. Both systems react by synthesizing stilbene synthase. The time courses of increase in enzyme activity, protein synthesis and mRNA activity were studied, and their relation to other activities of the cells was elaborated. The results show that, after applying the fungal elicitor, the system responds very quickly and selectively: within 2 hours the synthesis rate of stilbene synthase protein is increased more than 30-fold, the increase being detectable 40 min after induction. The first increase in translatable mRNA for stilbene synthase can be seen 20 min after application of the stimulus. Stilbene synthase synthesized in vivo was compared to stilbene synthase prepared by translation in vitro. There was no difference in size, and limited proteolysis did not indicate significant differences in the peptide structure of the primary translation product and the active enzyme.

Gene response upon illumination in forming mRNA encoding peroxisomal glycollate oxidase

Glycollate oxidase is a constituent of leaf peroxisomes. Its biosynthesis is, like the biosynthesis of many chloroplastic proteins, controlled by light, via phytochrome. The level of mRNA coding for glycollate oxidase was determined at different stages of greening of etiolated plant cells. The appearance of glycollate oxidase mRNA in the cytoplasm was measured by hybridization with cDNA containing part of the coding sequence for glycollate oxidase. cDNA was prepared from enriched mRNA, inserted into the Pst I site of pBR 322, and cloned in Escherichia coli DH-1. By differential colony hybridization and hybrid selection, a clone containing a 670 bp sequence complementary to mRNA encoding glycollate oxidase was selected and identified. Northern blot hybridization was used to investigate mRNA levels induced by light. It was found that continuous light affected the formation of glycollate oxidase mRNA. When a large population of microbodies was present in the cells being induced, the immediate mRNA increase was very pronounced, and was detectable as little as 20 min after the beginning of the light treatment. In contrast, a lag period in the mRNA increase was observed when the induction was performed with etiolated leaves which are characterized by the occurrence of a rather small population of microbodies. For comparison, we measured the time-course of formation of mRNA coding for a light-induced chloroplastic protein, i.e., a protein of the light-harvesting complex. The time-courses of levels of the two mRNAs indicate that the program of gene expression differs between the two particular proteins destined either for chloroplasts or for peroxisomes. The formation of glycollate oxidase mRNA could also be stimulated by a short pulse of light, a treatment of 15 s being a sufficient trigger.