La cisteína produce lisis de la membrana interna mitocondrial. Paralelamente a la lisis tiene lugar una disminución del contenido en los fosfolípidos totales de la membrana interna. El fósforo correspondiente a estos fosfolípidos desaparecidos se encuentra "ligado" a la fracción proteica. La fosfatidil colina y fosfatidil etanolamina son los fosfolípidos principalmente afectados, y su disminución es progresiva a lo largo de la incubación de las membranas internas con cisteína. Algunos antioxidantes y queladores (inhibidores de la producción de peróxidos de lípidos) bloquean el efecto de la cisteína sobre la membrana interna mitocondrial: no se producen cambios en la densidad óptica ni en el contenido en fosfolípidos. La cisteína aumenta la producción de peróxidos de lípidos de la membrana interna, hasta llegar a un máximo que coincide con el comienzo de la lisis (seguida por los cambios de la densidad óptica). Los fragmentos derivados de la lisis de la membrana interna por la acción de la cisteína, son diferentes desde el punto de vista morfológico, inmunológico y químico.

La replicación del DNA en bacterias ']. EuguiLa replicación del DNA es un tema de difícil acceso.Aunque ha sido objeto de amplias revisiones (1, 2, 3, 4), el tratamiento que recibe este proceso consiste frecuentemente en una recopilación de experiencias, hipótesis y modelos, sin una crítica ponderada de los mismos, faltando un ejercicio de síntesis y una visión coherente de los numerosísimos -y a veces contradictorios-datos experimentales En líneas generales, puede decirse que es abundante la información existente sobre la síntesis de DNA en procariotes in vitro.Sin embargo, quedan oscuros algunos puntos muy importantes, como son la relevancia de los datos encontrados in vitro con respecto a la situación in vivo, y los mecanismos de control de la replicación del DNA. ASPECTOS BÁSICOS

Se han separado tres fracciones, A, B y C. de la membrana interna mitocondrial de hígado de rata por tratamiento con ultrasonidos y centrifugación en un gradiente de sacarosa discontinuo, y se ha estudiado su distribución de actividades enzimilticas, citocromos y proteínas, con la finalidad de obtener datos sobre la composición heterogénea de la membrana interna. La fracción C era matriz mitocondrial. Contenía aproximadamente un 90 % de la activid ad de glutamato deshidrogenasa, y su distribución de proteínas en geles de poliacrilamida era similar a la de la matriz mitocondrial. La fracción B, con alrededor del 85 % de las actividades enzimáticas de la membrana interna y del total de citocromos, correspondena a la membrana de las crestas. En la fracción A se encontró sólo un 4 % de las actividades enzimáticas de la membrana interna mitocondrial y citocromos, y seria la membrana interna periférica en contacto con la membrana externa.

There is increasing interest in the determination of serum apolipoproteins (apo) A-I and B, because of the evidence indicating that they may be more useful laboratory indices of coronary heart disease than quantification of serum lipids. The lack of standardized methods, common reference ranges and clinical decision values are delaying the widespread use of apo A-I and B measurements. The possibility of obtaining accurate and comparable apo A-I and B values and reference limits has been enhanced by the development of reference materials for these apclipoproteins.l? In previous work, we devised a turbidimetric method for apo A-I and apo B with a Cobas Bio analyser and calculated reference intervals in a sample of 494 apparently healthy subjects.' In this study we have converted these intervals into values that may be obtained using three commercial methods for apo A-I and B which are calibrated against the International Federation of Clinical ChemistryWorld Health Organization (I FCC-WHO) reference standards for apolipoproteins.

We describe an immunoturbidimetric assay for estimating the concentration of apolipoproteins (apo) A-I and B in serum with a Cobas Bio centrifugal analyzer. Several analytical variables were studied: pH, temperature, wavelength, reaction time, sample pretreatment, antisera dilution, concentration of NaCl, phosphate buffer, and PEG 6000; a good optical response was obtained with small volumes of sample and antisera. Imprecision was low, with intrarun coefficient of variance (CV) from 1.1 to 2.8% and interrun CV from 1.8 to 3.2%. We demonstrated a good correlation between our method and radial immunodiffusion for apo A-I (r = 0.975) and apo B (r = 0.980). Reference values were calculated from a sample of 494 healthy subjects, and separate intervals for the ratio of apo A-I to apo B in gender and age subgroups were established.

Results from a multicenter evaluation of two new enzyme-linked immunosorbent assays [Enzymun-Test for follitropin (FSH) and lutropin (LH)] are presented and compared with results from 11 other commercial immunoassays, radioactive as well as nonradioactive. Enzymun-Test FSH and LH assays are suitable for automated systems and manual applications. The tests were reproducible (CV less than 5%), highly specific, and sensitive enough (less than 0.5 int. unit/L) to measure the hormones directly in almost all patients' samples, except for LH measurements in prepubertal children. We did not find interference by heterophilic antibodies or other factors. A comparison of assays for FSH found very good agreement among all modern two-site assays; competitive immunoassays almost invariably yielded systematically lower results for FSH, probably because of the heterogeneity of the International Reference Preparation (2nd IRP FSH, 78/549). For LH also we found good agreement, with no systematic differences among the various reagents. Guidelines for reference values with the new reagents are given.

Two new enzymoimmunoassays for FSH and LH adapted to the ES 600 analyzer (Boehringer Mannheim Diagnostics) were evaluated. The limit of detection was below 0.5 mIU/ml. Precision was excellent, the intra-assay coefficients of variation ranged from 1.2 to 2.2%, and the interassay variations from 2.0 to 2.8%. Both methods compared well with other commercial enzyme immunoassays, with correlation coefficients for FSH and LH of 0.988 and 0.974, respectively. There was no interference on the assays by the rheumatoid factor. The results of an external quality control assured the reliability of the measurements. Preliminary reference values were obtained.

Three fractions, A, B and C, were separated from rat liver inner mitochondrial membranes by sonication and centrifugation on a discontinuous sucrose gradient, and their distribution of enzyme activities, cytochromes and proteins was studied, in order to obtain data about the heterogeneous composition of the inner membrane. Fraction C was mitochondrial matrix. It contained about 90% of glutamate dehydrogenase activity, and its protein distribution in polyacrylamide gels was similar to that of mitochondrial matrix. Fraction B, with nearly 85% of enzyme activities and cytochrome contents of control inner membranes, would correspond to the crista membrane. Only 4% of cytochromes and enzyme activities of the inner membrane were found in fraction A, which would be the inner peripheral membrane, in contact with the outer membrane.

An end point turbidimetric method for the determination of C3c and C4 in serum using a centrifugal analyzer (Cobas Bio) is described. Several analytical factors were evaluated -pH, temperature, PEG and antibody concentration. Wide variations of temperature and pH did not significantly affect the turbidimetric reaction. A 20 g/L PEG concentration and 25-fold antiserum dilution were found satisfactory for the analysis. Precision of the assay was good and comparison with a RID method yielded an r value of 0.97. The procedure is simple and reliable.

Three fractions of submitochondrial particles were isolated by differential centrifugation of mitochondrial inner membranes incubated with 1 mM ascorbate. Proteins were separated by polyacrylamide gel electrophoresis and their pattern was found to be different for the three fractions. These results are in agreement with previous work which showed the dissimilar enzyme distribution and chemical composition of these submitochondrial particles and pointed out the heterogeneity of the inner mitochondrial membrane.

Phospholipid peroxidation of isolated rat liver inner mitochondrial membranes induced by either ascorbate or cysteine was accompanied by a release of flavins and coenzyme Q. A straight correlation between this release and the alteration of molecular species of phosphatidylcholine and phosphatidylethanolamine containing one saturated and one unsaturated fatty acid has been found. Peroxidation induced on molecular species of phosphatidylcholine and phosphatidylethanolamine containing only unsaturated fatty acids were accompanied by losses in enzyme activities of NADH-cytochrome c reductase and succinate cytochrome c reductase.

for fol- litropin(FSH) and lutropin(LH)) are presentedand com- paredwith resultsfrom 11 othercommercialimmunoas- says, radioactiveas well as nonradioactive.Enzymun- Test FSH and LH assays are suitablefor automated systemsand manualapplications. The testswere repro- ducible(CV <5%), highlyspecific,and sensitiveenough (<0.5 in unitlL) to measure the hormonesdirectlyin almostallpatients'samples,exceptforLH measurements in prepubertalchildren.We did not find interferenceby heterophilic antibodiesor otherfactors. A comparison of assays for FSH found very good agreementamong all moderntwo-siteassays;competitiveimmunoassays al- most invariablyyielded systematicallylower resultsfor FSH, probablybecause of the heterogeneity of the Inter- nationalReferencePreparation(2nd IRP FSH, 78/549). ForLHalsowe foundgood agreement,withnosystematic differencesamongthe variousreagents.Guidelinesfor referencevalueswiththe new reagentsare given. Addftlonal Keyphrases: interlaborato,ypenormancereference values variation, sourceof