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Biomedical subjects

G Frick

Publications and source records attributed to G Frick.

At least 19 recordsLinked to original sources
PubMed2001

POR C of Arabidopsis thaliana: a third light- and NADPH-dependent protochlorophyllide oxidoreductase that is differentially regulated by light.

During the sequencing of the genome of Arabidopsis thaliana a gene has been identified that encodes a novel NADPH-protochlorophyllide oxidoreductase (POR)-like protein (accession number AC 002560). This protein has been named POR C. We have expressed the POR C protein in Escherichia coli and have determined its in vitro activity. POR C shows the characteristics of a light-dependent and NADPH-requiring POR similar to POR A and POR B. The expression of the POR C gene differs markedly from that of the POR A and POR B genes. In contrast to the POR A and POR B mRNAs, the POR C mRNA has been shown previously to accumulate only after the beginning of illumination. In light-adapted mature plants only POR B and POR C mRNAs were detectable. The amounts of both mRNAs show pronounced diurnal rhythmic fluctuations. While the oscillations of POR B mRNA are under the control of the circadian clock, those of POR C mRNA are not. Another difference between POR B and POR C was found in seedlings that were grown under continuous white light. The concentration of POR C mRNA rapidly declined and soon dropped beyond the limit of detection, after these seedlings were transferred to the dark. On the other hand. POR B mRNA was unaffected by this light/dark shift. When seedlings were exposed to different light intensities, the amounts of POR B mRNA remained the same, while POR A and POR C mRNAs were modulated in an inverse way by these light intensity changes. POR A mRNA was still detectable in seedlings grown under low light intensities but disappeared at higher light intensities, while the mRNA concentration of POR C rose with increasing light intensities. These different responses to light suggest that the functions of the three PORs of Arabidopsis are not completely redundant, but may allow the plant to adapt its needs for chlorophyll biosynthesis more selectively by using preferentially one of the three enzymes under a given light regime.

Adaptation, Physiological↗
PubMed2000

Regulation of etioplast pigment-protein complexes, inner membrane architecture, and protochlorophyllide a chemical heterogeneity by light-dependent NADPH:protochlorophyllide oxidoreductases A and B.

The etioplast of dark-grown angiosperms is characterized by the prolamellar body (PLB) inner membrane, the absence of chlorophyll, and the accumulation of divinyl and monovinyl derivatives of protochlorophyll(ide) a [Pchl(ide) a]. Either of two structurally related, but differentially expressed light-dependent NADPH:Pchlide oxidoreductases (PORs), PORA and PORB, can assemble the PLB and form dark-stable ternary complexes containing enzymatically photoactive Pchlide-F655. Here we have examined in detail whether these polypeptides play redundant roles in etioplast differentiation by manipulating the total POR content and the PORA-to-PORB ratio of etiolated Arabidopsis seedlings using antisense and overexpression approaches. POR content correlates closely with PLB formation, the amounts, spectroscopic properties, and photoreduction kinetics of photoactive Pchlide, the ratio of photoactive Pchlide-F655 to non-photoactive Pchl(ide)-F632, and the ratio of divinyl- to monovinyl-Pchl(ide). This last result defines POR as the first endogenous protein factor demonstrated to influence the chemical heterogeneity of Pchl(ide) in angiosperms. It is intriguing that excitation energy transfer between different spectroscopic forms of Pchl(ide) in etiolated cotyledons remains largely independent of POR content. We therefore propose that the PLB contains a minimal structural unit with defined pigment stoichiometries, within which a small amount of non-photoactive Pchl(ide) transfers excitation energy to a large excess of photoactive Pchlide-F655. In addition, our data suggests that POR may bind not only stoichiometric amounts of photoactive Pchlide, but also substoichiometric amounts of non-photoactive Pchl(ide). We conclude that the typical characteristics of etioplasts are closely related to total POR content, but not obviously to the specific presence of PORA or PORB.

Arabidopsis↗
PubMed1998

Metronidazole prophylaxis to prevent infections after total abdominal hysterectomy.

METHODS: In a randomized double-blind study, 134 patients were given 500 mg metronidazole as an intravenous infusion immediately before operation for abdominal total hysterectomy and again 8 hours later and 124 patients received placebo. RESULTS: There was more wound infection, postoperative hospitalization was longer and the sedimentation rate on the sixth postoperative day was significantly higher in the placebo group. There was no difference in postoperative temperature. Postoperative wound infections occurred in 12% in the placebo group and 6% in the metronidazole group. Eight percent in the total material had urinary tract infections, the diagnosis was based on urine cultures. CONCLUSIONS: Prophylaxis with intravenous infusion of metronidazole is recommended in total hysterectomies.

Anti-Infective Agents↗
PubMed1998

Etioplast differentiation in arabidopsis: both PORA and PORB restore the prolamellar body and photoactive protochlorophyllide-F655 to the cop1 photomorphogenic mutant.

The etioplast plastid type of dark-grown angiosperms is defined by the accumulation of the chlorophyll (Chl) precursor protochlorophyllide (Pchlide) and the presence of the paracrystalline prolamellar body (PLB) membrane. Both features correlate with the presence of NADPH:Pchlide oxidoreductase (POR), a light-dependent enzyme that reduces photoactive Pchlide-F655 to chlorophyllide and plays a key role in chloroplast differentiation during greening. Two differentially expressed and regulated POR enzymes, PORA and PORB, have recently been discovered in angiosperms. To investigate the hypothesis that etioplast differentiation requires PORA, we have constitutively overexpressed PORA and PORB in the Arabidopsis wild type and in the constitutive photomorphogenic cop1-18 (previously det340) mutant, which is deficient in the PLB and Pchlide-F655. In both genetic backgrounds, POR overexpression increased PLB size, the ratio of Pchlide-F655 to nonphotoactive Pchl[ide]-F632, and the amount of Pchlide-F655. Dramatically, restoration of either PORA or PORB to the cop1 mutant led to the formation of etioplasts containing an extensive PLB and large amounts of photoactive Pchlide-F655.

Alleles↗
PubMed1997

Overexpression of light-dependent PORA or PORB in plants depleted of endogenous POR by far-red light enhances seedling survival in white light and protects against photooxidative damage.

The structurally related light-dependent protochlorophyllide (Pchlide) oxidoreductases PORA and PORB mediate the only light-requiring step in chlorophyll (Chl) biosynthesis in higher plants. Correlative evidence suggests that some in vivo functions of PORA and PORB may be unique, including a postulated photoprotective role for PORA. For example, wild-type Arabidopsis thaliana seedlings grown in non-photooxidative far-red light (cFR) resemble those grown in white light (WL), but they are yellow and do not green normally thereafter in WL. This defect is accompanied by the absence of detectable PORA and reduced levels of PORB expression. Here, direct evidence is provided that the presence of POR, either as PORA or PORB, can confer photoprotection in plants. In contrast to the wild-type, the plastids of transgenic PORA- or PORB-overexpressing Arabidopsis seedlings grown in cFR possess extensive prolamellar bodies. Upon a subsequent shift to WL, POR-overexpressing seedlings develop thylakoid membranes, accumulate large amounts of Chl and are viable at fluence rates lethal to the wild-type. Intriguingly, the plastid membrane architectures of greening transgenic seedlings seem to depend on whether PORA or PORB has been overproduced. POR-overexpressing seedlings shifted from cFR to WL of fluence rates from 20 to 500 muE m-2 sec-1 accumulate substantially higher amounts of Chl than does the wild-type. Furthermore, the WL fluence rate that permits maximal Chl accumulation increases from 8 muE m-2 sec-1 in the wild-type to 125 muE m-2 sec-1 in transgenic seedlings. POR overexpression during growth in cFR also correlates with a fourfold decrease in the steady-state content of Pchlide, a potentially lethal photosensitizer.

Agrobacterium tumefaciens↗
PubMed1996

Effect of methionine loading on 5-methyltetrahydrofolate, S-adenosylmethionine and S-adenosylhomocysteine in plasma of healthy humans.

1. Elevated plasma homocysteine concentration, either in the fasting state or after methionine loading, is an independent risk factor for vascular disease in man. Methionine loading has been used to investigate impaired methionine metabolism, especially of the trans-sulphuration pathway, but most studies have focused on changes in homocysteine. 2. We investigated the effect of methionine excess on total plasma homocysteine, 5-methyltetrahydrofolate (which is the active form of folate in the remethylation of homocysteine to methionine), S-adenosyl-methionine (the first metabolite of methionine) and S-adenosylmethionine) (the demethylated product of S-adenosylmethionine) over 24h in 12 healthy subjects. 3. As well as the expected increase in homocysteine (from 8.0 +/- 1.3 to 32.6 +/- 10.3 mumol/l, mean +/- SD, P < 0.001), S-adenosylmethionine showed a significant transient increase (from 37.9 +/- 25.0 to 240.3 +/- 109.2 nmol/l, P < 0.001), which correlated well with homocysteine (r2 = 0.92, P < 0.001). 5-Methyltetrahydrofolate values decreased significantly (from 23.2 +/- 7.2 to 13.1 +/- 2.9 nmol/l, P < 0.01), and gradually returned to baseline levels after 24h. No significant change over the time of measurement was found for S-adenosylhomocysteine. 4. The sequence of metabolic changes observed in this study strongly suggests that a change in either homocysteine or S-adenosylmethionine may cause a reduction in 5-methyltetrahydrofolate. This must be considered in evaluating the relationship between folate and homocysteine in vascular disease. The metabolic relationships illustrated in this study should be evaluated in the search for pathogenetic mechanisms of mild hyperhomocysteinaemia and vascular disease.

Adult↗
PubMed1996

Distinct roles for light-dependent NADPH:protochlorophyllide oxidoreductases (POR) A and B during greening in higher plants.

Light-dependent NADPH:protochlorophyllide oxidoreductase (POR), a nuclear-encoded plastid-localized enzyme, catalyzes the photoreduction of protochlorophyllide (Pchlide) to chlorophyllide in higher plants, algae and cyanobacteria. Angiosperms require light for chlorophyll (Chl) biosynthesis and have recently been shown to contain two POR-encoding genes, PorA and PorB, that are differentially regulated by light and developmental state. PorA expression rapidly becomes undetectable after illumination of etiolated seedlings, whereas PorB expression persists throughout greening and in adult plants. In order to study the in vivo functions of Arabidopsis POR A and POR B we have abolished the expression of PorA through the use of the phytochrome A-mediated far-red high irradiance response. Wild-type seedlings grown in continuous far-red light (cFR) display the morphology of white light (WL)-grown seedlings, but contain only traces of Chl and do not green upon transfer to WL. This cFR-induced greening defect correlates with the absence of PorA mRNA, the putative POR A protein, phototransformable Pchlide-F655, and with strongly reduced POR enzymatic activity in plant extracts. In contrast, a cFR-grown phyA mutant expresses the PorA gene, accumulates Chl and visibly greens in WL. Furthermore, constitutive overexpression of POR A in cFR-grown transgenic Arabidopsis wild-type seedlings restores Chl accumulation and WL-induced greening. These data demonstrate that POR A is required for greening and that the availability of POR A limits Chl accumulation during growth in cFR. POR B apparently provides a means to sustain light-dependent Chl biosynthesis in fully greened, mature plants in the absence of phototransformable Pchlide-F655.

Arabidopsis↗
PubMed1995

Identification of NADPH:protochlorophyllide oxidoreductases A and B: a branched pathway for light-dependent chlorophyll biosynthesis in Arabidopsis thaliana.

Illumination releases the arrest in chlorophyll (Chl) biosynthesis in etiolated angiosperm seedlings through the enzymatic photoreduction of protochlorophyllide (Pchlide) to chlorophyllide (Chlide), the first light-dependent step in chloroplast biogenesis. NADPH: Pchlide oxidoreductase (POR, EC 1.3.1.33), a nuclear-encoded plastid-localized enzyme, mediates this unique photoreduction. Paradoxically, light also triggers a drastic decrease in the amounts of POR activity and protein before the Chl accumulation rate reaches its maximum during greening. While investigating this seeming contradiction, we identified two distinct Arabidopsis thaliana genes encoding POR, in contrast to previous reports of only one gene in angiosperms. The genes, designated PorA and PorB, by analogy to the principal members of the phytochrome photoreceptor gene family, display dramatically different patterns of light and developmental regulation. PorA mRNA disappears within the first 4 h of greening, whereas PorB mRNA persists even after 16 h of illumination, mirroring the behavior of two distinct POR protein species. Experiments designed to help define the functions of POR A and POR B demonstrate exclusive expression of PorA in young seedlings and of PorB both in seedlings and in adult plants. Accordingly, we propose the existence of a branched light-dependent Chl biosynthesis pathway in which POR A performs a specialized function restricted to the initial stages of greening and POR B maintains Chl levels throughout angiosperm development.

Amino Acid Sequence↗
PubMed1991

[Seroprevalence of antibodies to human herpesvirus 6 (exanthema subitum; critical 3-day fever-exanthema in young children) in the population of Northern Germany].

We tested 989 sera of all age groups (patients and blood donors) from north eastern Germany (West Pomerania and Mecklenburg) and found 820 cases (82.9%) of specific human herpes virus type 6 (HHV 6) antibodies (IgG) gy indirect immunofluorescent assay. The seroprevalence rose to 83.6% when the 7 HHV 6-IgM positive results (0.7%) were included; moreover a further 23 sera (2.3%) showed specific HHV 6 antibodies of both classes (IgM and IgG). The antibody prevalence was constantly high at 90% from the age of 8 months up to the 71-80 years group, and it only decreased in the age group over 80. 93.2% of the newborn infants showed HHV 6-IgG antibodies (of maternal origin) in the cord blood; this prevalence is identical with that for females of reproductive age (92.7% in the 3rd decade, 93.7% in the 4th decade). No sex differences in seroprevalence were observed. The main immunization occurs in the first year of life but infection with HHV 6 at a later age is also well documented. We found the lowest seroprevalence in the 3rd and 4th postnatal months (when maternal immunity had disappeared); later the seroprevalence of specific antibodies rose very rapidly and by the 8th month the rate was the same as for the adult group. The theoretical possibility of prenatal infection due to HHV 6 exists, but the real risk of a first infection during pregnancy is very low, because only 7-8% are susceptible in this group.

Adolescent↗
PubMed1990

Plasma levels of cholecystokinin and gastrin during the menstrual cycle and pregnancy.

The objective of the present study was to measure plasma levels of cholecystokinin (CCK-8 and CCK-33,39) as well as of gastrin during the menstrual cycle and pregnancy. Cholecystokinin and gastrin levels were measured by radioimmunoassay. Before being assayed for cholecystokinin, plasma samples were submitted to HPLC which allowed separation of gastrin and cholecystokinin as well as between CCK-8 and CCK-33,39. Fasting CCK levels were 5.2 +/- 0.6 and 7.1 +/- 0.9 pM during the follicular and luteal phases of the menstrual cycle, respectively. The difference was significant (P less than 0.05). CCK levels were 8.7 +/- 1.2, 10.1 +/- 1.6 and 10.4 +/- 1.2 pM during the first, second and third trimester, respectively. CCK levels during pregnancy were significantly higher than during the menstrual cycle. The ratio between CCK-33,39 and CCK-8 appeared to increase during pregnancy. Gastrin levels remained unchanged during the menstrual cycle and pregnancy. The role of the high levels of cholecystokinin may be to stimulate the exocrine and endocrine pancreatic function during pregnancy. Furthermore, since cholecystokinin inhibits gastric emptying, it may play a role in the sickness of early pregnancy.

Cholecystokinin↗
PubMed1990

[Serotonin uptake of thrombocytes as a measure of thrombogenicity of adsorbents].

Serotonin intake into platelets is an active carrier-mediated metabolic achievement. This uptake may be reduced by unphysiological irritation on platelet membrane. Therefore, it is suitable for judgement of thrombogenicity of biomaterials. The 14C serotonin intake after blood contact with various adsorbents was investigated: Haemoresin (GDR), Adsorba 300 C (USSR) and syrendivinylbenzencopolymer FK 1621 (GDR). Only by the latter the serotonin intake was significantly reduced with 72.5 +/- 2.0% in comparison with siliconized glas (84.0 +/- 1.5%; p less than 0.001). Precision and analytical sensitivity of the method are high with a variation coefficient of 1.5 to 3.5%.

Adsorption↗
PubMed1988

Interactions of basophilic granulocytes and fat metabolism as indicators in thrombophilia.

In different groups of patients and blood donors with increased thrombophilic or arteriosclerotic risk we found some correlations between basophilic granulocyte values and lipid parameters. Basophilic granulocytes are one of the bodies own origin of sulfated mucopolysaccharides which protects endothelial cells and saves high density lipoprotein cholesterol, as we were able to find in blood donors.

Angina Pectoris↗
PubMed1987

[Behavior of thrombocytes in low-dose heparin therapy].

In a little prospective study it could be shown that a series of 10-51 low dose heparin injections may be followed by slight or unspecific thrombocyte diminutions without specific heparin antibodies being available. Depending on stress and trauma potential complement activations caused by heparin histon complexes may result in insignificant thrombocyte diminutions by liberating those factors activating platelets from granulocytes. These are not bound to interrupt heparin therapy or heparin prophylaxis.

Blood Platelets↗