Immunoaffinity Column Cleanup with Liquid Chromatography Using Post-Column Bromination for Determination of Aflatoxin B1 in Cattle Feed: Collaborative Study

A collaborative study was conducted to evaluate the effectiveness of an immunoaffinity column cleanup liquid chromatography (LC) method for determination of aflatoxin B1 in cattle feed at a possible future European regulatory limit (1 ng/g). The test portion was extracted with acetone–water (85 + 15), filtered, diluted with water, and applied to an immunoaffinity column. The column was washed with water to remove interfering compounds, and the purified aflatoxin B1 was eluted with methanol. Aflatoxin B1 was separated and determined by reversed-phase liquid chromatography (RP–LC) and detected by fluorescence after post column derivatization (PCD) involving bromination. PCD was achieved with either pyridinium hydrobromide perbromide (PBPB), used by 14 laboratories, or an electrochemical cell and addition of bromide to the mobile phase, used by 7 laboratories. Both derivatization techniques were not significantly different when compared by the t-test; the method was statistically evaluated for all laboratories together (bromination and PBPB). The cattle feed samples, both spiked and naturally contaminatedwithaflatoxinB1, were sent to 21 laboratories in 14 different countries (United States, Japan, and Europe). Test portions were spiked at levels of 1.2 and 3.6 ng/g for aflatoxin B1. Recoveries ranged from 74 to 157%. Based on results for spiked samples (blind pairs at 2 levels) as well as naturally con-taminated samples (blind pairs at 3 levels), the relative standard deviation for repeatability (RSDr) ranged from 5.9 to 8.7%. The relative standard deviation for reproducibility (RSDR) ranged from 17.5 to 19.6%. The method showed acceptable within-and between-laboratory precision for this matrix, as evidenced by HORRAT values, at the target levels of determination for aflatoxin B1. No major differences in RSD were observed, showing that the composition of the feeds was not a factor for the samples tested and that the method was applicable for all materials used.

Ultrasound surveillance after CAS and CEA: what's the evidence?

AIM

The rationale of clinical and Duplex ultrasound (DUS) surveillance after carotid endarterectomy (CEA) and carotid artery stenting (CAS) is the detection of recurrent stenoses and the prevention of future carotid-related cerebral ischemic events. This paper addresses the evidence for this approach.

METHODS

The multicenter randomized controlled trials (RCTs) published between 1990 and 2013 were reviewed with respect to DUS surveillance intervals, recurrent stenoses rates and recurrent ipsilateral stroke rates. In addition a Medline literature search from January 1990 until February 2014 was performed by use of the following keywords: "surveillance"; "carotid endarterectomy"; "carotid stenting"; "carotid artery surveillance"; "carotid artery stenosis". Finally we analyzed all carotid-related guidelines published between 2006 and 2013 for recommendations on DUS surveillance after CEA or CAS.

RESULTS

Nine RCT protocols (NASCET, ECST, ACST, ACAS, CAVATAS, SAPPHIRE, EVA-3S, CREST, and SPACE) showed similar follow-up intervals (at 1 month, 3 or 4 and at 6, and 12 months after CAS and CEA, then at least once a year). The incidence of a recurrent carotid stenosis (≥50%) or occlusion ranged around 6% four years after CEA or CAS. The annual incidence of any ipsilateral cerebral ischemic event was about 1% and 0.5% after CEA for a symptomatic or an asymptomatic stenosis respectively. Since the overall incidence of carotid recurrent stenosis and postprocedural strokes is low, DUS is questioned as necessary for all patients after CEA and CAS in prospective single center series. However, certain subgroups of patients (women, diabetics, patients with dyslipidemia, smokers) might have increased rates of restenosis after CEA or CAS. Data on DUS surveillance intervals following CAS is rare. Three out of 21 identified guidelines recommend long-term DUS surveillance, as the benefits are considered to exceed the risks. However, the level of evidence for any recommendation on DUS surveillance is consistently low.

CONCLUSION

Our literature review reveals only little evidence to support routine DUS after CEA within short intervals. Currently a practice with one periprocedural DUS and one DUS after 12 months after CEA seems to be reasonable. In patients with an ipsilateral restenosis≥50%, contralateral disease progression≥50% and in patients who are considered to be at higher risk of restenosis further DUS surveillance seems appropriate. Due to inconsistent long-term data on surveillance after CAS imaging at 6 months and then annually seems reasonable. Further studies on DUS surveillance are necessary.

Protease-catalyzed synthesis of the tripeptide CCK26–28, a fragment of CCK-8

Two enzymatically synthetic strategies of the tripeptide derivative PhAc-Asp(OMe)-Tyr-Met-OAl are reported. The second strategy gains the advantage of more economical starting materials, less reaction steps and a higher overall isolated yield of this tripeptide fragment over the first strategy. The effect of the acyl-donor ester concentration and structure, the C-alpha protecting group of the nucleophile, reaction media, enzyme and the carrier on the tripeptide derivative synthesis were studied. This tripeptide selected is a fragment of the cholecystokinin C-terminal octapeptide (CCK-8), a potential therapeutic agent in the control of gastrointestinal function and also a drug candidate for the treatment of epilepsy.

Total enzymatic synthesis of cholecystokinin CCK-5

This paper describes the enzymatic synthesis of the C-terminal fragment H-Gly-Trp-Met-Asp-Phe-NH2 of cholecystokinin. Immobilized enzymes were used for the formation of all peptide bonds except thermolysin. Beginning the synthesis with phenylacetyl (PhAc) glycine carboxamidomethyl ester (OCam) and H-Trp-OMe by using immobilized papain as biocatalyst in buffered ethyl acetate, the dipeptide methyl ester was then coupled directly with Met-OEt.HCl by alpha-chymotrypsin/Celite 545 in a solvent free system. For the 3+2 coupling PhAc-Gly-Trp-Met-OEt had to be converted into its OCam ester. The other fragment H-Asp(OMe)-Phe-NH2 resulted from the coupling of Cbo-Asp(OMe)-OH with H-Phe-NH2.HCl and thermolysin as catalyst, followed by catalytic hydrogenation. Finally PhAc-Gly-Trp-Met-Asp-Phe-NH2 was obtained in a smooth reaction from PhAc-Gly-Trp-Met-OCam and H-Asp(OMe)-Phe-NH2 with alpha-chymotrypsin/Celite 545 in acetonitrile, followed by basic hydrolysis of the beta-methyl ester. The PhAc-group is removed with penicillin G amidase and CCK-5 is obtained in an overall isolated yield of 19.6%.

Neutrophil function in peripheral arterial occlusive disease: the effects of prostaglandin E1

The role of polymorph nuclear neutrophils (PMN) in limb ischemia and reperfusion has been recognized only in recent years. The present study aimed to investigate the systemic and local (in femoral venous blood) effects of intra-arterially or intravenously applied prostaglandin E1 (PGE1) on systemic and ischemia-induced local changes in neutrophil function. Thirty patients with intermittent claudication were randomly assigned to intra-arterial or intravenous infusion of prostaglandin E1 (10 microg i.a. or 15 microg i.v. over 30 min). Prior to infusion femoral arterial and venous blood samples were obtained from the predominantly affected leg under resting conditions and immediately after a 3-min period of ischemia induced by suprasystolic thigh compression. After 24 h additional blood samples were obtained at baseline, following infusion of prostaglandin E1, and again after another 3-min period of ischemia following the prostaglandin E1 infusion. Intra-arterially administered prostaglandin E1 caused an increase in the PMN count by 3.5 +/- 2% (p<0.05) and a decrease in free oxygen radical production by 13 +/- 8% (p<0.05) measured by whole blood chemiluminescence. Additionally, a trend for lower PMN filterabilities (9 +/- 12%, NS) was observed. Intra-arterially infused prostaglandin E1 significantly reduced the ischemia-induced decrease in neutrophil filterability (arterial and venous blood difference after ischemia -- control: 22 +/- 17% (p<0.05); IA PGE1: 8 +/- 11% (NS), each compared to baseline). Intravenously administered prostaglandin E1 showed similar systemic effects as the intra-arterial application, but did not affect the ischemia-induced changes in neutrophil filterability. In conclusion, prostaglandin E1 reduces PMN activation in patients with peripheral arterial occlusive disease.

Guanosine 3':5'-cyclic monophosphate-dependent particulate protein kinase activity from yeast (Saccharomyces cerevisiae)

Continuing our studies on cGMP in growing yeast we detected a particulate cGMP dependent protein kinase (Pk-G), which was solubilized by detergents and NaCl. It achieves maximum activity at 25 degrees C and pH = 6.8, high concentrations of substrate proteins or cGMP produce saturation. Casein and histones are appropriate substrates, phosphatase-pretreated histone H-2a provokes outstandingly high activity. Pk-G differs from cAMP-dependent protein kinase (Pk-A) with respect to pH optimum, temperature tolerance above 50 degrees C, and stability. Partial purification is achieved by chromatography with DEAE-cellulose, Sepharose, and cGMP-substituted Sepharose. The latter step also markedly removes Pk-A. At least three proteins with Pk-G-activity and high cGMP-affinity are separated by polyacrylamide-gel-electrophoresis. Their apparent molecular masses, as deduced from comigrating marker proteins, differ considerably from those of other Pk-G's, but also of Pk-A's.

A particulate guanylate cyclase (EC 4.6.1.2) from growing yeast cells (Saccharomyces cerevisiae)

The detection of cGMP in yeast (Eckstein 1988), but lacking hints at guanylate cyclase from sequencing of the yeast genome, raised questions about existence, isoform, and regulation of guanylate cyclase from this organism. We found a particulate guanylate cyclase activity in yeast extracts, exhibiting properties of an integral membrane protein. Characteristics are: pH-optimum at pH 6.8, temperature-optimum around 60 degrees C, only slight stimulation by Mn2+. Sigmoidal enzyme kinetics indicate allosteric regulation, ATP and Ca2+ act as negative allosteric effectors. The enzyme activity is increased by yeast alpha-1 mating factor, and by sodium nitrite, thus showing properties of particulate as well as of soluble isoforms from other eukaryotes. The activation by alpha-1 mating factor suggests receptor functions, and a role in ascospore conjugation.

A dodecapeptide comprising the extended chain-alpha 4 region of the restriction endonuclease EcoRI specifically binds to the EcoRI recognition site

The restriction endonuclease EcoRI binds and cleaves DNA containing GAATTC sequences with high specificity. According to the crystal structure, most of the specific contacts of the enzyme to the DNA are formed by the extended chain region and the first turn of alpha-helix alpha 4 (amino acids 137-145). Here, we demonstrate that a dodecapeptide (WDGMAAGNAIER), which is identical in the underlined parts of its sequence to EcoRI amino acids 137-145, specifically binds to GAATTC sequences. The peptide inhibits DNA cleavage by EcoRI but not by BamHI, BclI, EcoRV, HindIII, PacI, and XbaI. DNA cleavage by XbaI is slowed down at sites that partially overlap with EcoRI sites. The peptide inhibits cleavage of GAATTC sites by ApoI, which recognizes the sequence RAATTY. It interferes with DNA methylation by the EcoRI methyltransferase but not by the BamHI methyltransferase. It competes with EcoRI for DNA binding. Based on these results, the DNA binding constant of the peptide to GAATTC sequences was calculated to be 3 x 10(4) M-1. DNA binding is not temperature-dependent, suggesting that binding of the peptide is entropy-driven. As the peptide does not show any nonspecific binding to DNA, its DNA binding specificity is similar to that of EcoRI, in spite of the fact that the affinity is much smaller. These results suggest that contacts to the phosphate groups in EcoRI mainly provide binding affinity, whereas the specificity of EcoRI is based to a large extent on sequence-specific base contacts.

3':5'-cyclic GMP in the yeast Saccharomyces cerevisiae at different metabolic conditions

cGMP is characterized as undetectable in yeast [(1986) Yeast Cell Biology, UCLA Symp. Mol. Cell Biol. (Hicks, J. ed.) p. 495], though in many organisms it contributes specifically to the regulation of metabolism. Here, we detected cGMP, using radioactive labeling and RIA techniques, after extraction of the cells with 1 mol/1 HClO4 at 37 degrees C. The cGMP 0.015-fold cAMP, about 3-times higher with exponentially growing cells than with pressed baker's yeast, and depends on glucose and O2 supply. The PDE inhibitors DMX and IBMX induce in growing cells an additional increase of the cGMP level, without similar effects on cAMP.

Evidence for cyclic GMP in the yeast Saccharomyces cerevisiae, and studies on its possible role in growth

The yeast Saccharomyces cerevisiae is shown to be equipped with cyclic GMP, the level of which ranges from 6 pmol/10(9) cells with pressed baker's yeast to 21 pmol/10(9) cells with exponentially growing cells. In extracts from synchronized growing yeast, cyclic GMP increases stepwise, being doubled at the time of each mitosis. Theophylline and 3-isobutyl-1-methylxanthine induce a rapid increase of cyclic GMP, followed by a premature formation of the septal cell wall between mother cell and bud. The effects of 3-isobutyl-1-methylxanthine are reversible. Dibutyryl-cyclic GMP, and, after a pronounced lag, also dibutyryl-cyclic AMP, induce a premature cell division, too. Cholera toxin induces premature cell divisions without a preceding increase in cyclic GMP. Neither theophylline nor 3-isobutyl-1-methylxanthine, cholera toxin or one of the dibutyryl-cyclic nucleotides modify the growth rate of the culture. None of the agents has significant effects on the level of cyclic AMP. The results suggest that cyclic GMP possibly controls an early step of mitosis, whereas ADP-ribosylation might govern a subsequent event.

[Prognosis of cardiogenic cerebral embolism]

In a retrospective study the reports of 211 cases of cardiogenic cerebral embolism--diagnosed on the base of neurological and cardiological findings--were analyzed in view of signs and findings of prognostic value. There were 21 patients with TIA, 39 cases of RIND and 151 patients with cerebral infarction, 60 of which showed mild and 91 severe neurological symptoms. 38 patients died during the period of hospitalization. While sex of the patients as well as vascular risk factors (hypertension, diabetes mellitus, cigarette smoking) did not influence the clinical course of the disease, patients with TIA or RIND in general were younger (about 5 years) than those with severe stroke. Prognosis of cardiogenic cerebral embolism depended to a great degree on the underlying heart disease. Cerebral embolism after myocardial infarction showed a better remission of symptoms than embolism in atrial fibrillation. In the group of valvular diseases the course of embolic strokes in mitral lesions was worse than in aortal valve disease. Prognosis was worst in endocarditis, both in view of neurological deficit and of mortality. Mostly, the cardiogenic emboli lead to infarctions of the middle cerebral artery territory (78 per cent) with a predilection for the left hemisphere. In media-syndromes the clinical course was significantly worse in patients with additional homonymous visual defect compared to incomplete infarctions. Initial disturbance of conscience reduced prognosis quoad vitam et restitutionem significantly. Of the neuroradiological findings, the detection of arterial occlusion or circulatory disturbance in angiography as well as the finding of an ischemic lesion in computed axial tomography (CAT) was correlated with a severe course of the embolic stroke. While 7 patients with hemorrhagic infarction in CAT-Scan showed no differences in the clinical course, the 14 patients with pathological cerebral spinal fluid findings in embolism had an unfavourable prognosis. The development of epileptic seizures did not influence the further course of the infarction to a significant extent. Results are compared with the current world literature.

Inhibition cyclic guanosine 3':5'-monophosphate of the soluble DNA polymerase activity, and of partially purified DNA polymerase A (DNA polymerase I) from the yeast Saccharomyces cerevisiae

DNA polymerase activity from extracts of growing yeast cells is inhibited by cGMP. Experiments with partially purified yeast DNA polymerases show, that cGMP inhibits DNA polymerase A (DNA polymerase I from Chang), which is the main component of the soluble DNA polymerase activity in yeast extracts, by competing for the enzyme with the primer-template DNA. Since the enzyme is not only inhibited by 3', 5'-cGMP, but also by 3',5'-cAMP, the 3'--:5'-phosphodiester seems to be crucial for the competition between cGMP and primer. This would be inconsistent with the concept of a 3'-OH primer binding site in the enzyme. The existence of such a site in the yeast DNA polymerase A is indicated from studies with various purine nucleoside monophosphates. When various DNA polymerases are compared, inhibition by cGMP seems to be restricted to those enzymes, which are involved in DNA replication, DNA polymerases with an associated nuclease activity are not inhibited, DNA polymerase B from yeast is even activated by cGMP. Though some relations between the cGMP effect and the presumed function of the enzymes in the living cell are apparent, the biological meaning of the observations in general remains open.

Synthesis of histone model sequences for immobilization on a cross-linked polyacrylate matrix

The synthesis of three peptide sequences which are useful as histone models, [Lys]5, [Lys]5-Pro and the sequence 17-27 of the lysine-rich histone from rabbit thymus Pro-Ala-Lys-Lys-Lys-Lys-Ala-Ala-Lys-Lys-Pro is described. Three different methods for the synthesis are applied. [Lys] 5 is synthesized from the amino end beginning with N alpha-acryloyl-N epsilon-Cbo-lysine by successive coupling of Cbo-lysine to yield the pentalysine monomer CH2=CH-CO-[Lys(Cbo)]5 which can be used directly for radical copolymerization. [Lys]5-Pro is synthesized according to the conventional peptide synthesis using the carbobenzoxy group for N alpha-protection and the tert,-butyl group for side chain protection. The carboxyl function is protected as tert.-butyl ester. The undecapeptide is synthesized in a similar manner. Instead of purifying the intermediate peptides by extraction, chromatography is used exclusively. The isolation of the unprotected peptides Lys-Pro, [Lys]3-Pro, [Lys]4-Pro, [Lys]5-Pro and Pro-Ala-[Lys]4-[Ala]2-[Lys]2-Pro and their characterization using amino acid analysis, electrophoreses and field desorption mass spectrometry is also reported.

Studies on interactions between immobilized lysine residues and oligomers of thymidylic and deoxyadenylic acids

Two groups of crosslinked polyacrylic gels with immobilized lysine and lysine peptides (Lys)5 and (Lys)5-Pro have been used as models for the chromatographic investigation of lysine-peptide-oligonucleotide interactions. One group carries carboxylic groups in addition to the peptide residues in the gel matrix; the other gel type contains no such carboxylic groups in the gel matrix. Nucleotides of the series (dT)2-5, p(dT)1-4, p(dT)1-4p, (dA)2-5, p(dA)1-5 and p(dA)1-4p were chromatographed on these gels under various conditions in an aqueous buffer. On the gels of the first group the nucleotides were retarded only slightly, the positive charges of the epsilon-amino groups being compensated partially or totally by the negatively charged carboxyl groups of the polymer matrix. On the gels of the second group, however, the oligonucleotides underwent specific interactions. These interactions were based primarily upon electrostatic forces between the positively charged epsilon-amino groups of the immobilized peptides and the negatively charged phosphate groups of the oligonucleotides. Our results indicate that, in addition to the electrostatic interaction, the conformation plays a crucial role. We explain the selectivity of the interaction with a conformation-fit mechanism. The origin of this mechanism, which creates specific interactions from unspecific forces, is discussed.

[Determination of the interaction of oligopeptides and oligonucleotides by a chromatographic technique (author's transl)]

Homologues of deoxyriboadenylic and deoxyribothymidylic acid show different degrees of retardation in a pentalysine gel. This chromatographic retardation is directly related to the strength of the interaction between the oligonucleotides and the immobilized pentalysine peptide residues. The strength of this interaction is determined by the total negative charge of the oligonucleotide, and by the nature of the constituent base of the oligonucleotide. The specificity of the interaction depends upon differences in conformation of the oligonucleotides.

Conformation affinity of cross-linked polyacrylic gels towards nucleobases, nucleosides and nucleotides

By radical copolymerisation of monofunctional acrylic derivatives with 1,4-tetramethylene dimethacrylate, cross-linked polyacrylic gels which show a high affinity towards nucleic acid residues have been synthesised. Using these polyacrlic gels, mixtures of nucleobases, nucleosides and nucleotides can be chromatographically separated to differing extents, in some cases quantitatively. The elution of nucleobases and nucleosides from the gel in the order Cyt, Gua, Thy, Ade (or dC, dG, dT, dA and C, G, U, A, respectively) shows that Ade (dA, A) is retarded to the highest degree from the gel matrix, Cyt (dC, C) to the lowest degree. Further, the results of the separations prove that the affinity of the polyacrylic gels is much stronger towards deoxyribonucleosides than towards ribonucleosides and nucleobases. The affinity of the polyacrylic gels towards nucleobases and nucleosides depends mainly upon their tertiary structure whereas the functional side groups of the polyacrylate matrix do not contribute significantly to the interaction of the gels.

[A micro method for the determination of the configuration of histidine in peptides: evidence for partial racemization during peptide synthesis (author's transl)]

A gas chromatographic method for the determination of small portions of D-histidine together with an excess of L-histidine (or vice versa) is described. Histidine is degraded to aspartic acid by reaction with ozone. The enantiomers are esterified with (+)-3-methyl-2-butanol. After N-trifluoroacetylation the volatile diastereoisomers are separated in glass capillaries coated with a chiral stationary phase and determined quantitatively. For precise evaluations the partial racemization during peptide hydrolysis must be accounted for. The method was applied to some histidine peptides and about 5% racemization was measured.

Investigation of peptide-nucleotide interactions using template chromatography. The specific recognition of peptide sequences by oligodeoxy adenylic acids

Polyvinylalcohol has been substituted with oligodeoxyadenylic acid and the resulting polyanion polyvinyl (pA)n irreversibly attached to DEAE-cellulose. Peptide-oligonucleotide interactions have been studied using a column chromatographic technique with the polyvinyl (pA)n-DEAE-cellulose as a stationary phase.

The investigation of peptide-oligodeoxythymidylic acid interactions using template chromatography

Poly(vinyl alcohol) has been substituted with oligodeoxythymidylic acid and the resulting polyanion irreversibly attached to DEAE-cellulose via ionic bonding. Peptide-oligonucleotide interactions have been studied using a column chromatography technique with the PV(pT)n-DEAE-cellulose as stationary phase. Of all the naturally occurring amino acids, only tryptophan and to a lesser extent tyrosine intreact significantly with the immobilized oligodeoxythymidylic acid residues under the conditions for base pairing. The homopolymers of tryptophan and tyrosine undergo greater retardation than the monomers, such that the effect is not additive but multiplicative. Thus Tyr-Tyr-Tyr shows an eightfold and Trp-Trp-Trp an approximately 30-fold larger retardation than tyrosine and tryptophan, respectively. The peptide-oligonucleotide interaction decreases considerably when nonaromatic amino acids are present in the peptide. Consequently, naturally occurring peptides and proteins which contain relatively small amounts of tryptophan and tyrosine compared with the nonaromatic amino acids undergo at the most only slight retardation on the PV(pT)n-DEAE-cellulose. The retention of oligonucleotides and peptides containing these aromatic amino acids is due in both cases mainly to base stacking (roughly 67% of the total interaction) but involves different mechanisms. Thus, the peptides interact preferably with the cellulose matrix whereas the oligonucleotides with the immobilized oligonucleotides. Interaction via hydrogen-bond formation makes up the remaining 33% of the total interaction. The oligonucleotides and peptides of the mobile phase interact with each other also via this mechanism. The strength of the d(pA-A-A) interaction is roughly that of Trp-Trp whereas d(pA-A-A-A) is weaker than Trp-Trp-Trp.

Acid-soluble deoxynucleotides and DNA synthesis in growing yeast after x-irradiation, II. Synthesis of deoxynucleoside tri- and monophosphates in synchronized and asynchronously growing cells

The behaviour of acid-soluble DNA precursors in synchronized and asynchronously growing yeast after X-irradiation is investigated by labeling techniques with 32Pi and by enzymic estimation. In prelabeled synchronized growing cells, radioactivity associated with deoxynucleoside triphosphates increases to maximum values shortly before each DNA replication, followed by a drastic decrease during S-phase. Radioactivity associated with monophosphates fluctuates, too, but with an opposite rhythm. These fluctuations apparently reflect quantitative changes of the DNA precursor pool during a cell cycle, as judged from the following findings: 1. Acid-soluble phosphorus is augmented stepwise. 2. "Specific" radioactivity from acid-soluble phosphorus compounds decreases steadily, indicating a continuous dilution of the labeled phosphorus pool with "cold" phosphorus. 3. Radioactivity associated with ribonucleotides fluctuates, too, but with a divergent rhythm.

In X-irradiated synchronice growing yeast, the fluctuations of the deoxynucleotide-associated 32P are disturbed only little. Maximum values appear nearly at the same time as in the control, they decrease to minor values even if DNA augmentation is delayed. This decrease is less drastic, however, than that during DNA replication in unirradiated yeast, yielding a slightly increased aver­ age label per generation time. At the same sime a rapid augmentation of monophosphate label is observed.

A pronounced increase of deoxynucleotide-32P is seen with X-irradiated asynchronously growing yeast, pointing to distinct radiosensitivities of the DNA/DNA precursor system in different cell stages. Neither 32P-fluctuations nor 32P-accumulation during DNA delay can be explained by cor­ responding observations with acid-soluble phosphorus or with ribonucleotide pools. Studies on 32P-incorporation also exclude radiation effects on cellular phosphorus uptake. Enzymic estimations of the deoxynucleoside triphosphate pools from asynchronously growing yeast rather exhibit a considerable increase of these substances during the radiation-induced delay of DNA augmentation. This accumulation of DNA precursors probably is caused by undisturbed synthesis, but reduced incorporation into DNA. The possible role of DNA repair in this system is discussed.

DNA turnover in growing yeast after X-irradiation

Growing yeast cells incorporate radioactivity from labeled nucleotides, deoxynucleotides, deoxyadenosine, and deoxycytidine into acid-insoluble material. Most of these compounds are in­ corporated predominantly into RNA, only dTMP and dTTP serve as effective and selective DNA precursors.

When yeast is prelabeled with dTMP, “specific” radioactivity of DNA decreases in the growing cells due to DNA augmentation. In X-irradiated yeast, “specific” radioactivity of DNA again decreases remarkably, though DNA augmentation of the growing giant cells in delayed. Simultaneously, radioactivity is rendered acid-soluble. Vice versa, X-irradiated unlabeled yeast incorporates radioactivity from labeled precursors into DNA, even if the DNA content of the cells does not increase.

When growing yeast cells are treated with cycloheximide, protein synthesis and DNA augmen­ tation are inhibited completely with 5·10-6 ᴍ cycloheximide. The decrease of “specific” radioactivity of DNA in X-irradiated cells, however, proves independent on an intact protein synthesis, even with 1·10-4 ᴍ cycloheximide.

The data provide clear evidence on DNA turnover in growing yeast after X-irradiation.

Acid-soluble deoxynucleotides and DNA synthesis in growing yeast after x-irradiation. I. Diphenylamine positive material in synchronized and asynchronously growing cells

In synchronized growing yeast, the level of acid-soluble purine deoxynucleotides, as determined by the diphenylamine reaction, fluctuates rhythmically: A rapid increase each time before DNA starts to replicate is followed by a considerable decrease during DNA augmentation. Delay of DNA replication by irradiation of synchronized yeast with 50 kr of X-rays results in a stepwise augmentation of deoxyribose derivatives. The fluctuating behaviour is restored, when DNA starts to increase, again. During asynchronous growth acid-soluble deoxyribosidic compounds are augmented with a considerably increased rate, when DNA replication is delayed by X-rays. The resulting unusual pool seize is maintained, even if DNA replication is resumed to a normal degree, but the rate of further increase is reduced to normal values. Parts of the rapidly accumulated deoxyribosidic material differ with some properties from purine deoxynucleotides.