Compartmentation of spermidine in Neurospora crassa

Exogenous spermidine elevating cadmium tolerance in Salix matsudana involves cadmium detoxification and antioxidant defense

In this study, exogenous spermidine role on Salix matsudana tolerance to cadmium was evaluated. Spermidine and cadmium presented antagonistic effects on the biomass, copper and zinc concentrations in S. matsudana. cadmium mainly distributed in the cell wall of subcellular fraction; 46.97%-60.43% of cadmium existed in a sodium chloride-extracted form. Cadmium contents in roots, leaves, and twigs ranged from 2002.67 to 3961.00, 111.59 to 229.72, and 102.56 to 221.27 mg/kg, respectively. Spermidine application elevated cadmium concentrations in the roots, cuttings, and cell wall and the ratio of deionized water-extracted cadmium, but decreased cadmium levels in the twigs and leaves and the fractions of cadmium extracted by ethanol and sodium chloride, respectively. Putrescine and malondialdehyde were important indicators of cadmium-induced oxidative damage. Exogenous spermidine alleviated the accumulation of superoxide anion, hydrogen peroxide, malondialdehyde via promoting the levels of spermidine, soluble protein, superoxide dismutase, reductive ascorbate, glutathione reductase, and glutathione peroxidase in S. matsudana leaves under the corresponding cadmium stress. The results indicated that S. matsudana was a candidate for cadmium rhizoremediation and extraction in leaves; the spermidine application enhanced the cadmium tolerance of S. matsudana through promoting cadmium accumulation in roots, cell wall, and less bioactive chemical forms and the antioxidative ability.

Endogenous polyamine function--the RNA perspective

Recent progress with techniques for monitoring RNA structure in cells such as ‘DMS-Seq’ and ‘Structure-Seq’ suggests that a new era of RNA structure-function exploration is on the horizon. This will also include systematic investigation of the factors required for the structural integrity of RNA. In this context, much evidence accumulated over 50 years suggests that polyamines play important roles as modulators of RNA structure. Here, we summarize and discuss recent literature relating to the roles of these small endogenous molecules in RNA function. We have included studies directed at understanding the binding interactions of polyamines with polynucleotides, tRNA, rRNA, mRNA and ribozymes using chemical, biochemical and spectroscopic tools. In brief, polyamines bind RNA in a sequence-selective fashion and induce changes in RNA structure in context-dependent manners. In some cases the functional consequences of these interactions have been observed in cells. Most notably, polyamine-mediated effects on RNA are frequently distinct from those of divalent cations (i.e. Mg²⁺) confirming their roles as independent molecular entities which help drive RNA-mediated processes.

Infection risk by dermatophytes during storage and after domestic laundry and their temperature-dependent inactivation

In the developed countries infections of the feet (tinea pedis, athlete's foot) and nails (onychomycosis) with the anthropophile fungus Trichophyton rubrum are most common. We examined the propagation of dermatophytes before and during domestic laundering. About 10% of the infectious material was transferred from contaminated textiles to sterile textiles during storage in a clothes basket simulation indicating a high infection risk during storage. This was evaluated with two quantification techniques: cultivation with subsequent colony counting and tracing of radioactively labelled propagating units. Both approaches reliably revealed similar results with the latter method reducing experimental time to few minutes compared to 2 weeks with the traditional method. The tracer technique allowed favourably to directly reflect the textile-bound infectious material at the moment of skin contact. To address the infection risk during domestic laundry, bioindicators with T. rubrum or the yeast Candida albicans were introduced into common domestic washing procedures with different temperature courses. While C. albicans did not survive any of the tests, T. rubrum could be recovered after washing at 30°C, indicating the risk potential of dermatophyte infections at home. Up to 16% of the initial fungus load was detected in the rinsing water. Washing at 60°C however, eliminated both pathogens, T. rubrum and C. albicans.

A Novel Protein Kinase CK2 Substrate Indicates CK2 Is Not Directly Stimulated by Polyamines in Vivo

The activity of the protein kinase (CK2) is enhanced in vitro by the binding of polyamines to the CK2beta regulatory subunit. The overexpression of ornithine decarboxylase (ODC), the rate-limiting enzyme in polyamine biosynthesis, also elevates CK2 kinase activity in primary keratinocytes and tissues of K6/ODC transgenic mice. In an effort to better characterize the mechanisms by which polyamines may affect CK2 in vivo, we constructed a transfectable CK2 substrate cDNA consisting of the enhanced green fluorescence protein appended with a canonical CK2 phosphorylation sequence (EGFP-S). In contrast to unmodified EGFP, the EGFP-S protein was extensively phosphorylated by CK2, and this phosphorylation was stimulated by the polyamine spermine in a dose-dependent manner. The in vivo phosphorylation of EGFP-S was examined in cell lines which inducibly express either wild-type CK2 holoenzyme or a CK2 holoenzyme which contains activating mutations in the polyamine-binding region of its CK2beta regulatory subunit. Neither the overexpression of ODC in either cell line nor the mutation of the CK2beta subunit conferred an increase in CK2 kinase activity as measured by the in vivo phosphorylation of EGFP-S. Rather, our data indicate that polyamines increase total CK2 kinase activity through increases in steady-state levels of both CK2alpha and CK2beta subunits. The overexpression of ODC resulted in a 3-fold increase in steady-state levels of both exogenous and endogenous CK2 transcripts but did not increase the half-life of wild-type or mutated CK2 protein. These data suggest that the regulation of intracellular CK2 by the polyamines may occur through mechanisms distinct from the direct stimulation of CK2 by polyamines in vitro as previously described.

Spermine causes caspase activation in leukaemia cells

Exposure of several leukaemia cell types to the polyamine spermine triggered caspase activation. In HL60 cells, the onset of caspase activity correlated with the accumulation of spermine, and was accompanied by the processing of the caspase-3 precursor and the digestion of the substrate proteins PARP and gelsolin. Spermine also induced the accumulation of cytochrome c in the cytosol. Caspase activation triggered by spermine was not blocked by antioxidants or inhibition of polyamine oxidase. The deregulation of polyamine uptake strongly sensitised the cells to spermine-induced caspase activation. These data show that an excessive intracellular level of spermine triggers caspase activation that is not mediated by oxidative mechanisms, and suggest a model where elevated free cytosolic polyamines may act as transducers of a death message.

Inhibition of porcine brain inositol 1,3,4-trisphosphate kinase by inositol polyphosphates, other polyol phosphates, polyanions and polycations

We have partially purified an enzyme activity that phosphorylates inositol 1,3,4-trisphosphate from porcine brain, rat liver and bovine testis by FPLC chromatography on Q-Sepharose anion-exchange resin and Heparin-agarose. The products of this reaction were inositol 1,3,4,6-tetrakisphosphate and inositol 1,3,4,5-tetrakisphosphate. The same enzyme appears to be responsible for both 6-kinase and 5-kinase activities against inositol 1,3,4-trisphosphate (the 6-kinase: 5-kinase activity ratio is approximately 4 to 1), has a pH optimum of approximately 6.8 and requires Mg2+ for activity. The Km values of the enzyme for inositol 1,3,4-trisphosphate and ATP were approximately 0.5 microM and approximately 100 microM, respectively. Inositol 3,4,5,6-tetrakisphosphate, inositol 1,3,4,6-tetrakisphosphate and inositol 1,3,4,5-tetrakisphosphate are all competitive inhibitors with K(i) values of 0.4 microM, 3 microM and 5 microM, respectively, well within their likely intracellular concentration ranges: they inhibited 6-kinase and 5-kinase activities equally. 2,3-Bisphosphoglycerate and spermine were also competitive inhibitors, with K(i) values of 0.8 mM an 12 mM, respectively. Dextran sulphate was a non-competitive inhibitor with a Ki of approximately 15 microM, and poly-L-lysine (IC50 approximately 200 microM), polyvinylsulphate (IC50 approximately 250 microM) and heparin (IC50 approximately 2 mg/ml) also inhibited. Inhibition by these compounds suggests that inositol 3,4,5,6-tetrakisphosphate (and to a lesser extent inositol 1,3,4,5-tetrakisphosphate and other naturally occurring intracellular ions) may restrict the synthesis of inositol 1,3,4,6-tetrakisphosphate and hence regulate the rate of inositol penta- and hexakisphosphate synthesis from receptor-generated inositol phosphates.

Effects of osmotic stress and growth stage on cellular pH and polyphosphate metabolism in Neurospora crassa as studied by 31P nuclear magnetic resonance spectroscopy

High-resolution 31P-NMR was employed to investigate the effects of growth stage and environmental osmolarity on changes of polyphosphate metabolism and intracellular pH in intact Neurospora crassa cells. Our study showed that changes of these parameters were growth-dependent. The ratio of polyphosphate to orthophosphate in vacuoles increased from 2.4 to 13.5 in N. crassa as cells grew from early log phase to stationary phase. Cytoplasmic pH and vacuolar pH changed, respectively, from 6.91 and 6.49 in early log phase cells to 7.25 and 6.84 in stationary phase cells. Hypoosmotic shock of N. crassa produced growth-dependent changes including: (i) a rapid hydrolysis of polyphosphate with a concomitant increase in the concentration of the cytoplasmic phosphate, (ii) an increase in cytoplasmic pH, and (iii) an increase in vacuolar pH. Early log phase cells produced the most dramatic response whereas the stationary phase cells appeared to be recalcitrant to the osmotic stress. Thus, 95% and 60% of polyphosphate in the early log phase and mid-log phase cells, respectively, disappeared in response to hypoosmotic shock, but little or no hydrolysis of polyphosphate occurred in stationary cells. The cytoplasmic pH and the vacuolar pH increased in response to hypoosmotic shock by 0.4 and 0.53 unit, respectively, in early log phase cells; and by 0.22 and 0.27 unit, respectively, in the mid-log phase cells. In contrast, hypoosmotic shock of the stationary phase cells did not cause any change in intracellular pH. The osmotic stress-induced polyphosphate hydrolysis and pH changes in early log and mid-log phase cells were reversible, suggesting that these changes were related environment osmolarity. Addition of polyamines or basic amino acids which are known to be sequestered in vacuoles did not effect polyphosphate metabolism.

Polyamine-mediated regulation of S-adenosylmethionine decarboxylase expression in mammalian cells. Studies using 5'-([(Z)-4-amino-2-butenyl]methylamino)-5'-deoxyadenosine, a suicide inhibitor of the enzyme

Cell proliferation is dependent on an adequate supply of the polyamines putrescine, spermidine and spermine. One of the key steps in the polyamine biosynthetic pathway is catalyzed by S-adenosylmethionine decarboxylase (AdoMetDC). In the present study we have used a newly synthesized enzyme-activated irreversible AdoMetDC inhibitor, 5'-([(Z)-4-amino-2-butenyl]methylamino)-5'-deoxyadenosine [(Z)-AbeAdo], to investigate the regulation of this enzyme. Treatment of mouse L1210 leukemia cells with (Z)-AbeAdo resulted in a total inhibition of their AdoMetDC activity followed by depletion of the spermidine and spermine content. The putrescine content, however, was dramatically increased after treatment with (Z)-AbeAdo. In spite of the cellular depletion of spermidine and spermine, only a minor inhibitory effect was obtained on cell growth, indicating that putrescine at a high concentration might partly replace spermidine and spermine in their growth-promoting functions. Cells grown in the presence of (Z)-AbeAdo exhibited an increased synthesis of AdoMetDC, which was counteracted by the addition of either spermidine or spermine. The change in AdoMetDC synthesis could not be fully explained by a change in the level of AdoMetDC mRNA, indicating also a translational control. Mammalian AdoMetDC is synthesized as a larger proenzyme, which is then cleaved into two subunits of different sizes. The conversion of the proenzyme into the subunits is a very rapid process, which is stimulated greatly by putrescine in vitro. However, the processing of the proenzyme in the (Z)-AbeAdo-treated L1210 cells was not affected by their very high putrescine content, indicating that the conversion might be saturated at low levels of putrescine, or that most of the putrescine in the (Z)-AbeAdo-treated L1210 cells might be bound to sites normally occupied by spermidine and spermine.

A new enzyme-linked immunosorbent assay (ELISA) for studying immunocytochemical procedures using an antiserum produced against spermidine as a model

Antiserum was produced in rabbits against the polyamine spermidine (Spd) conjugated to bovine serum albumin (BSA). The reactivity of the serum to Spd and a variety of structurally related compounds was quantified by a new immunocytochemical model system incorporating an enzyme-linked immunosorbent assay (ELISA) binding test. This is based on the principle of coupling these compounds to the wells of microtiter plate activated with poly-L-lysine and glutaraldehyde and incubating the wells by the indirect immunoperoxidase method. The antiserum showed a 25% cross reaction with spermine (Spm), putrescine (Put), and cadaverine (Cad), and a 1% cross reaction with 1,3-diaminopropane (Dap), but no cross reaction with monoacetyl polyamines and amino acids. The antibody binding was inhibited most effectively by absorption of the antiserum with N1-acetylspermidine and Spd in the ELISA inhibition test. Also, immunoblot analysis of the antiserum with nitrocellulose paper gave completely identical results to the ELISA binding tests. Spd-like immunoreactivities in human melanoma BD and neuroblastoma IMR 32 cell lines are presented as examples of the staining pattern obtained with the antiserum. Absorption of the serum with N1-acetylspermidine and Spd was demonstrated to abolish the immunostaining reaction. The immunohistochemical model is simple: amines and amino acids are bound in the same way as in aldehyde-fixed tissues and, in comparison to immunoblot analysis, the immunoreactivity can be more easily and accurately quantified by assay with the antibody. The model should prove useful in assessing the specificity of other antisera.

Spermidine nuclear acetylation in rat hepatocytes and in logarithmically growing rat hepatoma cells: comparison with histone acetylation

Spermidine acetylation has been studied in nuclear homogenates and in entire nuclei from rat hepatocytes and rat hepatoma tissue culture (HTC) cells, isolated at different stages of logarithmic growth, and compared to histone acetylation. Under all experimental conditions, N8-acetylspermidine was the predominant product of the reaction (90%). Unlike histone, spermidine acetylation in HTC cell and hepatocyte entire nuclei was almost absent or strikingly reduced relative to acetylation using nuclear homogenates as the enzyme sources. This was due to the lack of a free minor pool of spermidine, most likely lost during the purification of entire nuclei. Thus, preincubation of intact nuclei in the presence of spermidine restored activities to values observed using nuclear sonicates. Spermidine acetylation in HTC cell nuclei fluctuated moderately during cell growth, being stimulated immediately after initiation of proliferation and decreasing progressively as cultures reached high cell density. This pattern corroborated that of N8-acetylspermidine intracellular accumulation induced by culturing cells in the presence of 1 mM 7-amino-2-heptanone, a competitive inhibitor of N8-acetylspermidine deacetylase. Histone acetylation during HTC cell growth was not markedly different qualitatively from that of spermidine. Moreover, spermidine and histone acetylations in hepatocyte nuclei were of the same order of magnitude as those seen in rat hepatoma cell nuclei. Finally, inhibition of deacetylation of N8-acetylspermidine had no apparent deleterious effects on cell and growth. It remains to be determined whether the acetylation step is of higher physiological importance, in particular, and as discussed in nuclear spermidine turnover.

Proton potential-dependent polyamine transport by vacuolar membrane vesicles of Saccharomyces cerevisiae

Vacuolar membrane vesicles of Saccharomyces cerevisiae accumulated spermine and spermidine in the presence of ATP, not in the presence of ADP. Spermine and spermidine transport at pH 7.4 showed saturation kinetics with Km values of 0.2 mM and 0.7 mM, respectively. Spermine uptake was competitively inhibited by spermidine and putrescine, but was not affected by seven amino acids, substrates of active transport systems of vacuolar membrane. Spermine transport was inhibited by the H(+)-ATPase-specific inhibitors bafilomycin A1 and N,N'-dicyclohexylcarbodiimide, but not by vanadate. It was also sensitive to Cu2+ or Zn2+ ions, inhibitors of vacuolar H(+)-ATPase. Both 3,5-di-tert-butyl-4-hydroxybenzilidenemalononitrile (SF6847) and nigericin blocked completely the spermine uptake, but valinomycin did not. [14C]Spermine accumulated in the vesicles was exchangeable with unlabeled spermine and spermidine. However, it was released by a protonophore only in the presence of a counterion such as Ca2+. These results indicate that a polyamine-specific transport system depending on a proton potential functions in the vacuolar membrane of this organism.

Opposite responses of nuclear spermidine N8-acetyltransferase and histone acetyltransferase activities to regenerative stimuli in rat liver

Experiments performed in different models of hepatic regeneration at the time of maximal DNA synthesis, determined by thymidine kinase activity assay, demonstrated that spermidine N8-acetyltransferase activity increased 48 hr after CCl4 administration (2-fold), 72 hr after CCl4 plus phenobarbital (3-fold) and 24 hr after partial hepatectomy (4.5-fold). On the contrary, at these times histone acetyltransferase activity diminished (approximately twofold) and was unchanged compared with control values in the liver of hepatotoxin-treated and hepatectomized rats, respectively. Histone acetylation was, however, enhanced 1.5-fold before the onset of DNA replication (14 hr), and 3.4-fold after the peak of DNA synthesis (32 hr) in the liver of hepatectomized rats. alpha-Difluoromethylornithine, a specific and irreversible inhibitor of ornithine decarboxylase that was administered to hepatectomized rats, blocked polyamine synthesis, thymidine kinase activity and consequently liver regeneration 24 hr after the surgery. In those conditions, spermidine N8-acetyltransferase activity was decreased approximately twofold, whereas histone acetyltransferase activity was elevated approximately twofold. All these effects were reversed by putrescine coadministration. Altogether, these findings showed that nuclear spermidine N8-acetyltransferase and histone acetyltransferase activities were regulated in opposite ways during the processes associated with liver regeneration. Moreover, they suggested that the polyamines themselves might have a direct or indirect role in this regulation.

Polyamine toxicity in Neurospora crassa: protective role of the vacuole

We used mutant strains of Neurospora crassa to define the discretionary capacity of this species for excess putrescine. The spe-3 mutant, which accumulates putrescine internally, and the puu-1 mutant, which accumulates toxic levels of putrescine from the medium, both sequestered large excesses of putrescine in vacuoles. Concomitantly in puu-1, inorganic polyphosphate increased modestly and some of the monovalent cation of the vacuole was discharged. These two factors contribute to the increased capacity for polyamines in this fungus. Putrescine, however, can exceed the capacity of vacuoles such that they no longer protect the cytosol from toxic levels of the amine. The puu-1 mutant illustrates the importance of the sequestration of intracellular polyamines, as well as the control of polyamine uptake through the cell membrane.

Management of polyamine pools and the regulation of ornithine decarboxylase

The management of polyamine synthesis and polyamine pools differs fundamentally from that of most other small molecular-weight endproducts. The polyamines are vital to growth and important cellular functions, but they are toxic in excess. I argue here that their multivalent cationic character, leading to binding to cell constituents, precludes fluent feedback inhibition of synthesis. This has led to the development of elaborate alternative regulatory mechanisms controlling ornithine decarboxylase, the key initial enzyme of the pathway. Poorly regulated polyamine synthesis and the toxicity of polyamines impose upon cells a need to control uptake and to dispose of excess polyamines. Recent data on polyamine transport suggest unorthodox mechanisms of accomplishing these functions.

The genetics of polyamine synthesis in Neurospora crassa

New mutations of the polyamine pathway of Neurospora crassa fell into three categories. The majority affected ornithine decarboxylase and lay at the previously defined spe-1 locus. One mutation, JP100, defining the new spe-2 locus, eliminated S-adenosyl-methionine decarboxylase and led to putrescine accumulation. Revertants of this mutation suggested that the locus encodes the enzyme. Two other mutations, LV105 and JP120, defined a third locus, spe-3. Strains with these mutations also accumulated putrescine and were presumed to lack spermidine synthase activity, which catalyzes the formation of spermidine from putrescine and decarboxylated S-adenosylmethionine. The three spe loci lay within about 20 map units of one another on the right arm of Linkage Group V in the order: centromere-spe-2-spe-1-spe-3. The requirement for spermidine for growth was much less in spe-2 and spe-3 mutants than in spe-1 mutants, which do not accumulate putrescine. This suggested that putrescine fulfills many, but not all, of the functions of spermidine, or that high levels of putrescine render spermidine more effective in its essential roles.

Uptake, intracellular binding, and excretion of polyamines during growth of Neurospora crassa

In Neurospora crassa mycelia, the amounts of the main polyamines, putrescine and spermidine, are approximately 0.8 and 18 nmol/mg, dry weight. We wished to know what determines these pool sizes. In the growth medium, externally added polyamines enter cells largely by a nonsaturable, diffusional system. In a mutant unable to polyamines, internal and external spermidine appear to equilibrate across the cell membrane during growth. However, this was true only after an intracellular "sink," with a capacity equal to the amount of spermidine found in wild-type cells, had been saturated. We speculate that internal anionic binding sites, detectable in permeabilized cells, sequester virtually all of the spermidine normally found in exponentially growing N. crassa. Further evidence for this view was that in mature, stationary cultures, excess spermidine is excreted. Putrescine is also excreted if its concentration in the cell is abnormally high. The control of pool size by intracellular binding and excretion may be an advantage in this pathway, because feedback inhibition does not prevail, enzyme regulation is by comparison slow, and excessive polyamines are toxic.

Involvement of antizyme in stabilization of ornithine decarboxylase caused by inhibitors of polyamine synthesis

Contrary to previous findings, ornithine decarboxylase (ODC) was stabilized by treatment of cells with DL-alpha-difluoromethylornithine, an enzyme-activated irreversible inhibitor of ODC. Both this inhibitor and cyclohexylamine, a spermidine synthase inhibitor known to stabilize ODC, caused decreases in the antizyme/ODC ratio by increasing ODC content and conversely decreasing antizyme content. The relationship between cellular polyamine levels and antizyme content indicated that spermidine is the most important polyamine for antizyme induction. These results suggest that antizyme is involved in the mechanism underlying the stabilization of ODC by inhibitors of polyamine synthesis and support the hypothesis that cellular polyamines regulate ODC degradation via antizyme.

Polyamine transport in Neurospora crassa

Polyamine transport in Neurospora crassa is concentrative and energy dependent in a dilute buffer. The saturable systems governing the uptake of putrescine (Km = 0.6 mM), spermidine (Km = ca. 0.24 mM), and spermine (Km = 0.07 mM) share components, as indicated by mutual inhibition among the polyamines. In addition, nonsaturable components prevail for putrescine and spermidine, particularly the former. Radiolabeled substrates, once in the cell, are released only slowly, even if unlabeled polyamines are included in the incubation medium. Permeabilization of cells with n-butanol leads to partial release of internalized 14C-polyamines, and the remainder is almost wholly exchangeable with added, unlabeled polyamine. Polyamine uptake was inhibited by the polyamines themselves and by a polyamine analog, methylglyoxal bisguanylhydrazone, but only weakly and incompletely by the basic amino acids arginine and ornithine. Uptake of putrescine and spermidine was inhibited by monovalent cations, Ca2+, and certain other components of the growth medium. As a result, uptake from the growth medium was very slow and largely by way of the nonsaturable uptake mechanism.

Mechanisms and significance of polyamine stimulation of various protein kinase reactions

An overview of the work on polyamine effects on certain protein kinase reactions is presented. In general, the reactions catalyzed by the messenger-independent protein kinases but not by cyclic nucleotide-, Ca2+-, Ca2+-calmodulin-, and Ca2+-anionic lipid-dependent protein kinases, are markedly enhanced by polyamines. The extent of this stimulation depends critically on the nature of the protein substrate and several other factors. A variety of other polycationic compounds including Co3+(NH3)6, polybrene, and certain aminoglycoside antibiotics exert polyamine-like effects in the same reactions. These observations suggest that the charge properties rather than any strict chemical structure play a role in the action of polyamines. Available data do not support a specific "cofactor" function of these amines for the protein kinases involved in the polyamine-stimulable reactions. It appears that the action of polyamines is mediated via their influence on the conformational status of the protein substrates thereby altering the availability of the phosphorylatable sites to the active sites on the protein kinases. Although this notion is supported by several lines of evidence, at present a role of the influence of polyamines on both the substrate and enzyme cannot be ruled out. Possible physiological relevance of the polyamine-stimulable protein kinase reactions observed in the in vitro experiments remains problematic in the absence of precise knowledge on the "effective" or free concentrations of intracellular polyamines.

Determination of the polyamine content of rat heart mitochondria by the use of heparin-sepharose

Heparin-sepharose has been utilized to remove polyamines adsorbed to the cytoplasmic surface of rat heart mitochondria. The results obtained can be summarized as follows: Heparin-sepharose removes 90% of the spermine, 98% of the spermidine, and 98% of the putrescine adsorbed. Polyamine contents of chromatographed mitochondria amount to 2.66 and 0.36 nmol spermine and spermidine, respectively, per mg of mitochondrial protein.

Determination of various 15N-enriched spermidines with gas chromatography-mass spectrometry

A novel method for the determination of all eight kinds of variously 15N-enriched spermidines including the natural one is described using gas chromatography-mass spectrometry. After strict assignments of nitrogen(s) in fragment ions split from pentafluoropropionyl derivative of spermidine with 20 eV impact, six fragments (P7 and P10 containing N1 and N4 of spermidine, P8 and P11 containing N4 and N8, and P14 and P15 containing N1, N4, and N8 as designated in the text) were found to be useful for calculating relative contents of the various spermidines. The calculation was carried out by a computer program with the input of 20 relative intensities observed at m/z 259-261, 273-275, 379-381, 393-395, 436-439, and 464-467. Reliability of the method was examined by measuring known mixtures of authentic spermidines. In an experiment testing reproducibility, an average coefficient of variation was 4.8% with a reasonable accuracy for the eight spermidines. Linearity of relative ratios of 15N-enriched spermidines to the natural one was assured with an average correlation coefficient of 0.996. The present method was applied for spermidine synthase reaction, and it was confirmed that the enzyme from rat prostate could not discriminate against 15N of putrescine.