Investigation of the clinical value of assessing renal size on computed tomography in autosomal dominant polycystic kidney disease

We examined relationship between serum creatinine concentration (Scr) and renal size on CT scans on 32 occasions in 25 patients with autosomal dominant polycystic kidney disease (ADPKD). As a result, a significant correlation was observed when the Scr was less than 5 mg/dl, as shown by the correlation coefficient (r) and P values of 0.803 and 0.0001, respectively. However, these values changed to 0.482 and 0.0093, respectively when 2 cases with Scr 6.2 and 6.4 mg/dl were included, and further changed to 0.005 and 0.9775 when an additional 4 cases with Scr 7.8, 9.9, 11.1 and 20.1 mg/dl were included. Renal size is therefore thought to be a useful parameter of renal function when the Scr is less than 5 mg/dl in ADPKD, but not when the Scr exceeds 6 mg/dl, and is regarded as useless for predicting the time at which dialysis would be required.

Endoscopic transnasal antrochoanal polypectomy: an alternative to the transantral approach

The use of functional endoscopic sinus surgery has been limited typically to management of chronic sinusitis, nasal polyposis, and recurrent acute sinusitis. Antrochoanal polyps (ACPs) traditionally have been resected using a Caldwell-Luc sinusotomy. We used the endoscopic approach, however, in the treatment of five cases of ACP. There was recurrence in one case, but the polyp was successfully removed endoscopically. In the other four cases there has been no evidence of recurrence at a maximum follow-up of 24 months. We believe that transnasal endoscopic antrochoanal polypectomy is an excellent surgical option; there is significantly less postoperative morbidity than with the transantral approach, and rates of complete cure are similar.

Analysis of the inhibition of commitment of murine erythroleukemia (MEL) cells to terminal maturation by N6-methyladenosine

Treatment of cultured murine erythroleukemia (MEL or Friend) cells with N6-methylated derivatives of adenosine inhibited erythroid cell differentiation induced by various agents. N6-Methyladenosine (N6mAdo) inhibited initiation of commitment to terminal maturation and prevented accumulation of hemoglobin in a concentration-dependent manner. Treatment with N6mAdo slowed cell growth without causing substantial inhibition in the rate of DNA synthesis and a marked decrease in viability and clonogenic potential of MEL cells. Furthermore, N6mAdo decreased the cytoplasmic accumulation of beta(major) globin mRNA and affected its structural integrity in MEL cells. Cells pre-exposed to N6mAdo failed to initiate commitment as early as control cells upon challenge with the inducer dimethyl sulfoxide. N6mAdo-induced inhibition of commitment was not reversed but rather was potentiated by the presence of adenine, L-homocysteine and/or L-methionine, agents involved in the active methylation cycle. To this respect, N6mAdo-induced inhibition of commitment was found to be different from that caused by cordycepin (3'-deoxyadenosine, an inhibitor of RNA methylation and mRNA polyadenylation). The latter inhibition was fully reversed by the addition of L-methionine. These findings indicate that N6-methyladenosine: (a) blocks a central process that is required for initiation of commitment; and (b) decreases accumulation of beta (major) globin mRNA, causes mRNA degradation and prevents hemoglobin synthesis. Due to the differential sensitivity of N6mAdo- and cordycepin-induced blockade of commitment to L-methionine, these agents inhibit commitment by acting via two different mechanisms impinging on the final pathway of MEL erythroid cell maturation.

Suppression of longitudinal versus transverse conduction by sodium channel block. Effects of sodium bolus

BACKGROUND

Arrhythmias resulting from treatment with sodium channel-blocking antiarrhythmic drugs have been successfully treated with sodium infusion, although the mechanism underlying this effect is uncertain.

METHODS AND RESULTS

In this study, we used a multielectrode array to examine the effects of O-desmethyl encainide (ODE), a potent sodium channel-blocking metabolite of encainide, on conduction in canine ventricle. ODE depressed both longitudinal and transverse conduction velocities in a plasma concentration-related fashion (r = -0.74, -0.60; p less than 0.001). At ODE concentrations less than or equal to 300 ng/ml (n = 34), conduction velocity was depressed to the same extent in the longitudinal (-21.9 +/- 8.4%, SD) and transverse orientations (-22.0 +/- 8.8%). However, at concentrations greater than 300 ng/ml (n = 17), conduction was significantly more impaired longitudinally than transversely (-44.5 +/- 11.7% versus -34.4 +/- 13.7%, p less than 0.02). In 12 animals with high concentrations (mean, 432 +/- 32 ng/ml), a 5-meq/kg bolus of sodium chloride over 1 minute immediately increased conduction velocity; this effect was significantly greater and longer lasting in the longitudinal orientation. In two animals, conduction block in the longitudinal orientation was documented at high plasma ODE and was immediately reversed by sodium bolus.

CONCLUSIONS

We conclude that the major effect of sodium in animals with excess sodium channel block is improvement of longitudinal propagation; this effect may underlie the antiarrhythmic action of sodium in the analogous clinical setting.

Providing health care to Hawaii's elderly

Hawaii's rapidly aging population is a challenge for Hawaii's health care providers. What with the high cost of care, limited health care resources, and a rapidly increasing population of frail elderly patients living in the community, will our medical practices be able to adapt to the care of patients who require more time and who will have not only multiple medical illnesses but complicated psychosocial conditions as well? Will our health care facilities be prepared for the typically longer stay and more expensive older patient? Will the cost of care in Hawaii keep on rising? Who will pay? Will this challenge turn into a crisis?

Stereoselective genetically-determined interaction between chronic flecainide and quinidine in patients with arrhythmias

1. Recent reports have indicated a role for the P450IID6 polymorphism in the stereoselective disposition of single doses of the antiarrhythmic flecainide. 2. In this study, we evaluated the effects of adding low dose quinidine, a potent inhibitor of P450IID6, to chronic flecainide therapy in patients with arrhythmias. 3. In five extensive metabolizer patients, quinidine significantly reduced the clearance of R-(-)-flecainide, from 395 +/- 121 (s.d.) to 335 +/- 88 ml min-1. This change was attributable to a decrease in metabolic clearance, was accompanied by decreased formation of the two major metabolites of flecainide and was not observed in a poor metabolizer subject. The renal clearance of R-(-)-flecainide rose significantly. 4. Quinidine did not alter the clearance of S-(+)-flecainide. 5. The pharmacologic effects of flecainide therapy (QRS widening, % arrhythmia suppression) were slightly, but not significantly, increased. 6. In extensive metabolizer patients receiving chronic flecainide, increased plasma concentrations will develop if P450IID6 is inhibited.

Pharmacology of the class III antiarrhythmic agent sematilide in patients with arrhythmias

Sematilide, a close structural analog of N-acetylprocainamide, prolongs cardiac action potentials in vitro, whereas it does not depress maximum action potential upstroke slope, a "class III" action. This report outlines an evaluation of the clinical pharmacologic actions of sematilide in 14 patients with chronic high-frequency nonsustained ventricular arrhythmias. In all, 36 intravenous infusions (range 0.15 to 1.5 mg/kg over 15 minutes) were administered in a dose-ranging, placebo-controlled study design. Sematilide prolonged rate-corrected QT (QTc) in a dose- and concentration-related fashion, did not alter PR or QRS, and slowed heart rate at high concentrations (greater than or equal to 2 micrograms/ml). The relations between dose and total area under the time-concentration curve, dose and peak plasma concentration, and peak plasma concentration and increase in QTc were linear (r = 0.66 to 0.92; p less than 0.001). QTc increases of approximately equal to 25% were seen at plasma concentrations of approximately equal to 2.0 micrograms/ml. The mean elimination half-life (+/- SD) was 3.6 +/- 0.8 hours, and most of a dose (77 +/- 13%) was recovered unchanged in the urine. Plasma concentrations greater than or equal to 0.8 micrograms/ml suppressed arrhythmias (5 patients) or aggravated them (3), including 1 patient who needed cardioversion for an episode of torsades de pointes (2.7 micrograms/ml). Thus, sematilide exerts class III actions in patients. Further studies to evaluate the role of this antiarrhythmic mode of action should be conducted at doses designed to limit QTc increases.

Distinct receptor and regulatory properties of recombinant mouse complement receptor 1 (CR1) and Crry, the two genetic homologues of human CR1

The relationship between the characterized mouse regulators of complement activation (RCA) genes and the 190-kD mouse complement receptor 1 (MCR1), 155-kD mouse complement receptor 2 (MCR2), and mouse p65 is unclear. One mouse RCA gene, designated MCR2 (or Cr2), encodes alternatively spliced 21 and 15 short consensus repeat (SCR)-containing transcripts that crosshybridize with cDNAs of both human CR2 and CR1, or CR2 alone, respectively. A five SCR-containing transcript derived from a second unique gene, designated Crry, also crosshybridizes with human CR1. We have previously shown that the 155-kD MCR2 is encoded by the 15 SCR-containing transcript. To analyze the protein products of the other transcripts, which are considered the genetic homologues of human CR1, we have expressed the 21 and the 5 SCR-containing cDNAs in the human K562 erythroleukemia cell line. We demonstrate that cells expressing the 21 SCR transcript express the 190-kD MCR1 protein. These cells react with five unique rat anti-MCR1 monoclonal antibodies, including the 8C12 antibody considered to be monospecific for MCR1. In addition, these cells efficiently form rosettes with mouse C3b-bearing sheep erythrocytes. In contrast, cells expressing the five SCR-containing Crry transcript are strongly recognized by an anti-human CR1 antibody that also defines the mouse p65 protein. Using a functional assay that measures the surface deposition of C3 activated via the classical complement pathway, we show that Crry/p65-expressing cells have a markedly decreased amount of C3 deposited on them as compared with control cells expressing the antisense construct or cells expressing MCR1 or MCR2. This suggests that Crry has intrinsic complement regulatory activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Cooperative effects of hemin and anthracyclines in promoting terminal erythroid maturation in K562 human erythroleukemia cells

Simultaneous exposure to 30 microM hemin and 3 x 10(-8) M aclacinomycin (ACL) or mussetamycin for 6 days led to terminal differentiation of K562 cells. The number of hemoglobinized cells and the total hemoglobin content of cells treated with both ACL and hemin exceeded the sum of the corresponding values induced in response to each of these two agents when used alone. Although neither ACL nor hemin alone induced substantial morphological maturation, 40%-45% of cells treated with both agents developed the morphological characteristics of orthochromatophilic normoblasts, a level of maturation not previously reported for this highly malignant cell line. Subcloning of K562 cells that had been treated with both ACL and hemin in inducer-free plasma clots revealed a 50% decrease in the clonogenic potential of these cells, even though the cells in the original cultures were still growing at only a moderately decreased rate. Despite the apparent terminal maturation of K562 cells induced with both ACL and hemin, with an advanced level of morphologic maturation and hemoglobin synthesis accompanied by a loss of proliferative capacity, these cells remained incapable of producing beta-globin chains and hence hemoglobin A.

Genetically determined steady-state interaction between encainide and quinidine in patients with arrhythmias

A genetically determined pharmacokinetic and pharmacodynamic interaction between quinidine and single doses of encainide in healthy volunteers has previously been described. In subjects with the extensive metabolizer phenotype, quinidine blunted encainide-induced QRS prolongation (a marker of sodium channel block) because it impaired encainide biotransformation to the potent active metabolites O-desmethyl encainide (ODE) and 3-methoxy-O-desmethyl encainide. Therefore, the purpose of this study was to test the hypothesis that quinidine would inhibit sodium channel block (and by inference arrhythmia suppression) during encainide therapy in patients with the extensive metabolizer phenotype. Surprisingly, however, in eight extensive metabolizer patients, the extent of QRS prolongation during chronic encainide therapy was unaltered by quinidine (139 +/- 21 vs. 139 +/- 22 msec) whereas arrhythmia suppression was enhanced (64 +/- 22 to 77 +/- 19%; P = .05). Plasma concentration data demonstrated that although encainide metabolism to ODE was partially impaired by quinidine, subsequent 3-methoxy-O-desmethyl encainide formation from ODE was virtually completely inhibited; thus steady-state plasma ODE remained unchanged whereas plasma encainide increased 10-fold (21 +/- 30 to 240 +/- 118 ng/ml; P less than .05). In contrast, no changes in disposition or in pharmacodynamics were observed in two poor metabolizers. It is concluded that the effect of this drug interaction in patients is determined by differential sensitivities to inhibition by quinidine of encainide O-demethylation and subsequent ODE 3-methoxylation. Evaluation of potential drug interactions should include assessment of possible genetic factors as well as of steady-state effects.

Stability and purity profile of gonadorelin acetate: a high-purity gonadotropin-releasing hormone

Recently, several reports of adverse reactions after pulsatile GnRH (gonadorelin hydrochloride) infusion therapy have appeared in the medical literature. Although the cause of these reactions has been associated with GnRH itself, the contributions of impurities and degradation products in the administered drug have not been determined, suggesting that the use of high-purity material may be advantageous in controlling unwanted side effects. This study evaluates the purity and long-term stability of a new GnRH product, gonadorelin acetate (Lutrepulse, Ortho Pharmaceutical Corporation). Both the purity and potency of the drug substance, the lyophilized product for injection, and the reconstituted material that would be transferred to the infusion pump system were monitored using high-performance liquid chromatography. The gonadorelin acetate drug substance was found to be stable for at least 12 months when stored at 24 degrees C in 50% relative humidity, and showed no degradation even under accelerated storage conditions. Similarly, the lyophilized product also showed excellent stability for at least 18 months when stored at 24 degrees C in 50% relative humidity. Upon reconstitution, gonadorelin acetate was found to be stable for at least 45 days when stored at 24 degrees C or 37 degrees C.

Use of peripheral vessels for exchange transfusion

During a five and a half year period, exchange transfusions were performed through the peripheral vessels in 201 of the 214 infants (94%) who required either double volume or partial plasma exchange transfusions. Peripheral vessel exchange transfusion is simple, practicable, and safe with few complications. Technical difficulties in catheterizing the peripheral artery and vein may be overcome by using a 24 gauge catheter, which causes no more catheter induced haemolysis than standard umbilical catheters.

[F3, a fractionated extract of Astragalus membranaceus, potentiates lymphokine-activated killer cell cytotoxicity generated by low-dose recombinant interleukin-2]

Success with rIL-2 immunotherapy of human cancer appears to depend on the administration of high doses which are frequently associated with excessive toxicity. Future use of rIL-2 will require certain modifications based on the use of lower doses of rIL-2 without significant loss of antitumor efficacy. The authors tested in vitro the possibility of potentiating the activity of rIL-2 in terms of LAK cell generation. The authors hypothesized that co-incubation of LAK cell precursors with a Chinese herbal extract (F3) of Astragalus membranaceus (an immune modulator currently under study in the authors' laboratory), along with a low concentration of rIL-2 would generate levels of LAK cell activity equivalent to those generated by high concentrations of rIL-2 alone. The authors found: (1) a 10-fold potentiation of rIL-2 activity manifested by tumor cell killing activity of 80% resulting from LAK cell generation with F3 plus 100 u/ml of rIL-2 versus 76% generated by 1000 u/ml of rIL-2 alone; (2) a significant reduction in the number of effector LAK cells required for equicytotoxic reaction following LAK cell generation with F3 plus rIL-2 compared to rIL-2 alone. The authors conclude that potentiation of antitumor activity mediated by rIL-2 in low concentrations is possible by the concomitant use of another immune modulator such as Astragalus membranaceus.

Late metabolic acidosis and poor weight gain in moderately pre-term babies fed with a casein-predominant formula: a continuing need for caution

When our neonatal unit opened in 1984 our formula feeding policy for moderately preterm babies was for casein-predominant rather than "humanized" whey-predominant milk formulae to be given. However, an early cluster of cases of late persistent metabolic acidosis prompted an investigation into the acid-base status and weight gain in preterm infants. This study of 70 healthy, moderately preterm (32-35 weeks) Chinese babies has convincingly shown that a casein-predominant low protein formula is associated with significant metabolic acidosis, persisting sometimes for as long as 8 weeks, and poor weight gain when compared with infants fed on either a humanized or a special low-birthweight formula. This is an important message for the many neonatal units in developing countries where the cost of humanized formulae might initially seem prohibitive, encouraging instead casein-predominant formulae when breast milk is not available. Any additional expense incurred in using humanized formulae will be compensated for by the shortened time spent in hospital.

Effect of acute experimental influenza A virus pneumonia on concentration of alpha 1-acid glycoprotein in mouse serum

In mice, the mean serum concentration of the acute-phase reactant alpha 1-acid glycoprotein increased 34-48% over 14 days following experimental induction of pneumonitis by intranasal inoculation of influenza A virus. Inoculation of undiluted (hemagglutination titer 640) and 10(-1) dilution of virus was followed by development of maximum concentrations of alpha 1-acid glycoprotein in serum at seven days, of 334 micrograms/ml, compared to a concentration in control mice inoculated with irradiated inactivated virus of 225 micrograms/ml (P = 0.002). Infection with 10(-2) virus yielded a peak serum alpha 1-acid glycoprotein of 301 micrograms/ml at four days, 34% higher than in control mice at four days (P = 0.04). There were no differences in alpha 1-acid glycoprotein concentrations among virus-infected mice. Influenza A virus pneumonitis was confirmed histologically, by virus isolation, and by serologic testing, but no inoculum-dependent differences were observed. On day 7, there was a direct relationship demonstrated between the severity of pneumonitis evaluated histologically and the serum alpha 1-acid glycoprotein concentration (r = 0.50; P less than 0.02). Influenza A pneumonia in mice is associated with increased concentrations of alpha 1-acid glycoprotein in serum; the increase may be directly related to the severity of the pulmonary inflammation.

Elderly people taking non-steroidal anti-inflammatory drugs are unlikely to have excess renal impairment

The importance of possible adverse effects on renal function of non-steroidal anti-inflammatory drugs has been widely discussed. Elderly people have been thought to be particularly at risk. We therefore studied simple indices of renal function and plasma potassium in 54 patients with a mean age of 85 years, 27 taking these drugs and 27 controls. Twenty five of our 54 patients were also taking diuretics. Non-steroidal anti-inflammatory drugs did not affect renal function or plasma potassium in these patients.

Hemin increase production of beta-like globin RNA transcripts in human erythroleukemia K-562 cells

Previous studies have indicated that control and hemin-treated human erythroleukemia K-562 cells fail to produce adult-type beta-globin mRNA transcripts and to translate them into nascent beta-globin chains. Expression of the beta-globin DNA sequences in K-562 cells can occur, however, under certain conditions. To readdress this issue and to examine the possibility of whether these cells produce immature and untranslatable beta-globin RNA transcripts, we prepared total cytoplasmic RNA from control and inducer-treated cells and performed Northern blot hybridization analysis using 5' end-labeled fragments of the human beta-globin DNA rather than 3' end fragments as probes. Although hybridization of both cytoplasmic and nuclear K-562 RNA with a 32P-labeled 3' end fragment (1.6kb Bam H1 cut) coding for a large part of the first exon of beta-globin failed to detect beta-globin RNA transcripts, hybridization with a 5' end 32P-Labeled 2.0kb Bam H1 fragment (coding for the third exon and part of the second) revealed the presence of relatively small (less than 7S) RNA molecules both in nuclear and cytoplasmic fraction. S1 nuclease mapping of both cytoplasmic and nuclear RNA with the use of 5' end-labeled 2.0 kb Bam H1 fragment of human beta-globin DNA indicated protection of a small portion located 64 bp 5' upstream from the Bam H1 site of the second exon. The amount of protected portion was relatively higher in K-562 cells undergoing erythroid maturation.(ABSTRACT TRUNCATED AT 250 WORDS)

Hazards of angioscopic examination: documentation of damage to the arterial intima

The fiberoptic scope is increasingly used in the coronary and peripheral arteries to quantitate the degree and type of arterial obstructive disease and to inspect the results of procedures such as bypass grafting and laser irradiation of obstructive lesions. Since little is known about this instrument's potential complications, we passed a variety of fiberoptic scopes (1.8 to 3.6 mm outer diameter) in fresh postmortem pig coronary arteries and live monkey and canine peripheral arteries, and observed the intraluminal anatomy through the angioscope. No perforations were created, but ridges rising from the vascular luminal surface, avulsion of the endothelial lining, and small flaps attached at one end to the vessel wall were observed. Histologically, subintimal and medial tears were evident. Inserting large diameter scopes or making frequent passes (10 to 100) in coronary arteries increased intravascular injury. The use of small diameter flexible scopes or infrequent passes (less than 10) in the larger iliac and femoral arteries of live monkeys and dogs resulted in a lower frequency of myointimal sloughing or flap formation. Current fiberoptic scopes are not ideal angioscopes; they have a rigid tip, cannot be steered adequately, and are relatively stiff, resulting in a high probability of intraluminal injury, especially when used in small tortuous arteries. To decrease the risk of such injury, we recommend gentle manipulations while passing the scope and use of the smallest diameter scope possible. We further suggest limited use of the fiberscope, or at least limiting the number of passes in small vessels such as coronary arteries.

The measurement of phospholipase A2 activity in human myometrium: physiological and pathological implications

Phospholipase A2 activity was measured in human myometrium obtained at hysterectomy in a group of 41 patients using a double isotope ratio assay based on the liberation of [14-C] oleic acid from 1-palmitoyl-2-[14-C] oleoyl phosphatidylcholine. The enzyme was shown to be calcium independent and to have an optimum pH of 7. There was no significant difference (Mann Whitney U test) in myometrial phospholipase A2 activity between proliferative and secretory phases of the menstrual cycle (ranges: 3.88-30.8 and 0.47-25.85 nmol/mg protein per h respectively) but there was a significant (P less than 0.01) increase in activity in myometrium from uteri with fibroids (median 11.33, range 2.18-30.88 nmol/mg protein per h) compared to those without fibroids (median 6.94, range 0.31-25.85 nmol/mg protein per h). Myometrial phospholipase A2 activity was significantly lower (P less than 0.001) in the 33-40 age group (median 4.71, range 0.31-6.94) compared to the 41-50 age group (median 11.35, range 2.18-30.88 nmol/mg protein per h). In the 51-55 age group phospholipase A2 activity (median 8.71, range 2.5-17.71 nmol/mg protein per h) was not significantly different from that of the other two groups. The increase in activity in the 41-50 age group was not due to the increased incidence of uterine fibroids. These findings suggest that myometrial phospholipase A2 may be important in the pathophysiology of the uterus.

Cerebrovascular ultrasound imaging

Advancements in technology have brought noninvasive diagnosis of cerebrovascular disease to a high level of accuracy in a relatively short period of time. Conventional duplex sonography allows precise vessel localization and Doppler quantification. The further refinement of color flow imaging promises to simplify the examination and add considerable confidence to the diagnosis. Regardless of the technology used, ultrasound evaluation of the carotid arteries remains a difficult examination to perform, and excellent results are only possible with meticulous technique. The astute sonographer or sonologist will use all aspects of available ultrasound technology to the fullest. Careful evaluation of a seemingly overwhelming array of parameters will result in an impressive degree of diagnostic accuracy.

Analysis of hemin-induced protection of human hemopoietic cells from the cytotoxic effects of anthracyclines

Experiments were performed with K562 erythroleukemia cells to further characterize the observation that hemin protects hemopoietic cells from the cytotoxic effects of anthracycline drugs. The present studies demonstrate that this protective effect of hemin applies only to anthracyclines and not to other classes of antineoplastic agents. Hemin interferes with the cellular accumulation of various anthracyclines, as measured by cytofluorography, and prevents binding of anthracyclines to isolated cell nuclei. Exposure of K562 cells to hemin retards the anthracycline-induced arrest of cells at the G2-M interphase of the cell cycle and permits cells to undergo continuing division as demonstrated by clonal growth in plasma clot cultures. Furthermore, hemin decreases the ability of anthracyclines to unwind simian virus 40 supercoiled DNA in vitro. The protective effect of hemin fails to occur if cells have been preincubated with this agent for 72 h before they are exposed to Adriamycin in the absence of hemin. The findings suggest that hemin prevents anthracycline-induced cytotoxicity by acting at several levels. These effects may be mediated by direct interactions of hemin with DNA and perhaps other cellular constituents or by molecular complex formation between hemin and anthracyclines at intracellular sites.

Purification and characterization of an endonuclease from fruiting caps of basidiomycete Coprinus cinereus

An endonuclease was purified from the cap tissues of basidiocarp of Coprinus cinereus collected at early meiotic prophase. It has an optimal activity at pH 7.0 and 37 degrees C. It is a cationic enzyme with a molecular mass of 22 kDa by gel filtration, and contains a 12-kDa and a 14-kDa peptide as revealed by SDS gel electrophoresis and Western blot analysis. An antiserum was produced in rabbits against the purified Coprinus endonuclease. The specificity of this antiserum was demonstrated in a dot-blot analysis and, more critically, in an immunoinhibition of endonuclease activity. The Coprinus endonuclease requires Mg2+ and/or Ca2+ as co-factors. Ca2+ is more efficient than Mg2+ while the effect of combining both co-factors is the highest. The Coprinus endonuclease has a substrate preference for single-strand and supercoiled DNA. It gives only single-strand nicks on supercoiled DNA at low enzyme concentration and limited time of incubation. At high enzyme concentration and/or long incubation time, double-strand fragmentation occurred. As is discussed, this endonuclease is believed to be involved in the early phase of meiotic recombination.