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Changes in Targeting Efficiencies of Proteins to Plant Microbodies Caused by Amino Acid Substitutions in the Carboxy-terminal Tripeptide 总被引:7,自引:0,他引:7
Hayashi Makoto; Aoki Masahiro; Kondo Maki; Nishimura Mikio 《Plant & cell physiology》1997,38(6):759-768
It has been demonstrated that the carboxyl terminus of microbodyenzymes functions as a targeting signal to microbodies in higherplants. We have examined an ability of 24 carboxy-terminal aminoacid sequences to facilitate the transport of a cytosolic passengerprotein, ß-glucuroni-dase, into microbodies in greencotyledonary cells of trans-genic Arabidopsis. Immunoelectronmicroscopic analysis revealed that carboxy-terminal tripeptidesequences of the form [C/A/S/P]-[K/R]-[I/L/M] function as amicrobody-targeting signal, although tripeptides with prolineat the first amino acid position and isoleucine at the carboxylterminus show weak targeting efficiencies. All known micro-bodyenzymes that are synthesized in a form similar in size to themature molecule, except catalase, contain one of these tripeptidesequences at their carboxyl terminus. (Received April 14, 1997; Accepted April 8, 1997) 相似文献
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Human chorionic gonadotropins (hCGs) highly purified from the urine of patients with trophoblastic diseases and of healthy pregnant women contain approximately four mucin-type sugar chains in one molecule. The structures of these sugar chains were studied comparatively by using a new sensitive method to obtain mucin-type sugar chains quantitatively as radioactive oligosaccharides from a small amount of glycoproteins. The mucin-type sugar chains of all hCGs include sialylated and nonsialylated Gal beta 1----3GalNAc and Gal beta 1----4GlcNAc beta 1----6(Gal beta 1----3)GalNAc. In the case of normal hCG and hydatidiform mole hCG, oligosaccharides containing the tetrasaccharide core occupy approximately 10% of the total mucin-type sugar chains. The ratio of the tetrasaccharide containing oligosaccharides is increased prominently to approximately 60% in choriocarcinoma hCG. The proportion in invasive mole hCG was also increased, but less than the proportion of choriocarcinoma hCG. 相似文献
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Functional expression of the calcium release channel from skeletal muscle ryanodine receptor cDNA 总被引:7,自引:0,他引:7
Combined patch-clamp and fura-2 measurements were performed to study the calcium release properties of Chinese hamster ovary (CHO) cells transfected with the rabbit skeletal muscle ryanodine receptor cDNA carried by an expression vector. Both caffeine (1-50 mM) and ryanodine (100 microM) induced release of calcium from intracellular stores of transformed CHO cells but not from control (non-transfected) CHO cells. The calcium responses to caffeine and ryanodine closely resembled those commonly observed in skeletal muscle. Repetitive applications of caffeine produced characteristic all-or-none rises in intracellular calcium. Inositol 1,4,5-trisphosphate (IP3) neither activated the ryanodine receptor channel nor interfered with the caffeine-elicited calcium release. These results indicate that functional calcium release channels are formed by expression of the ryanodine receptor cDNA. 相似文献
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Procathepsin H in kidney and liver microsomal lumen was identified to have a molecular mass of 41 kDa by immunoblot analysis. The proenzyme was then concentrated by applying the microsomal contents to a concanavalin A-Sepharose column. When the concanavalin A-adsorbed fraction was incubated at pH 4.0 at 20 degrees C, the activity measured with synthetic substrate increased 3.5 times over that of the control after 24 h incubation. Immunoblot analysis showed that acidic treatment caused the disappearance of procathepsin H. Thus the proenzyme might be processed to the mature enzyme under acidic conditions. The marked increase of enzymatic activity and the conversion of proenzyme were completely blocked with pepstatin which is a potent inhibitor of aspartic proteases. These results suggested that a protease for processing procathepsin H might be cathepsin D, a major lysosomal aspartic protease. Therefore, procathepsin H seems to be synthesized first in the enzymatically inactive form in endoplasmic reticulum and successively converted into the active form in lysosomes during biosynthesis. 相似文献
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The catalase molecule in germinating pumpkin cotyledons is synthesizedas a precursor (59-kDa) form, whose relative molecular massis larger than the mature enzyme (55-kDa). Although both typesof molecules are localized in the microbodies, the 59-kDa specieshas been shown to be present predominantly in the leaf peroxisomesisolated from green cotyledons, while the 55-kDa species ispredominantly in the glyoxysomes from etiolated cotyledons [Yamaguchiet al. (1984) Proc. Natl. Acad. Sci. USA, 81: 4809]. We examinedthe distribution of the 59- and 55-kDa catalase molecules indark- and light-grown tissues of pumpkin seedlings as well asin other plant species, using the immunoblotting technique.The ratios of the 59- and 55-kDa catalase species differed inthe pumpkin tissues examined. Light interferes with the conversionof the 59-kDa precursor to the 55-kDa form, especially in thecotyledons. The effect of light was less pronounced in the rootsand hypocotyls, indicating that the light regulation of theconversion is tissue-specific. Dark- and light-grown cotyledonsfrom cucumber and watermelon seedlings showed a similar lightregulation, suggesting that cucurbitaceous plants possess similarlight-regulatory mechanism. From the analysis of catalase proteinfrom various plant tissues, a limited correlation between molecularforms of catalase and different microbody populations was observed. (Received September 6, 1986; Accepted December 4, 1986) 相似文献
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In cells of cyanobacterium Anabaena variabilis grown under ordinaryair (low-CO2 cells), the transport of both CO2 and HCO3was significantly enhanced by Na+. This effect was pronouncedas the external pH increased. When low-CO2 cells were treatedwith an inhibitor of carbonic anhydrase (CA), only CO2 transportbut not HCO3 transport, was inhibited. The initial rateof photosynthetic carbon fixation as a function of the concentrationof internal inorganic carbon (IC) was practically the same irrespectiveof whether CO2 or HCO3 was externally supplied. Theseresults suggest that IC is actively transported through theplasma membrane in a form of HCO3 probably by some transporterand that the transmembrane Na+ gradient is involved in thisIC transport system. Free CO2 may be hydrated by CA to HCO3and then transported to the cells by this transporter. On the other hand, CO2 is actively taken up by cells grown withair containing 5% CO2 (high-CO2 cells) though the enhancingeffect of Na+ was much smaller in high- CO2 cells than in low-CO2cells. The initial rate of fixation as a function of internal IC concentrationindicated that the rate of the carboxylation reaction of accumulatedIC is higher in I0W-CO2 cells than in high-CO2 cells. The studieswith ethoxyzolamide indicated that even in low-CO2 cells, CAdoes not function inside Anabaena cells. These results suggestthat inside the low-CO2 cells of Anabaena, some mediator(s)facilitates the transport of IC to RuBPCase. (Received January 23, 1987; Accepted April 24, 1987) 相似文献