DNA profile similarity in a subdivided population

There is considerable debate regarding the effect of population subdivision (heterogeneity) on the probability of a chance or coincidental match between two DNA samples studied with respect to multiple, polymorphic genetic markers. We have theoretically investigated the relationship between the average similarity between two randomly chosen DNA samples and the probability of an identical match between these samples, and population subdivision. Our results demonstrate that the average similarity and the match probability is smaller when population heterogeneity exists as compared to a random mating population with identical gene frequencies, for realistic values of heterogeneity. In other words, ignoring subdivision provides numerical values only slightly larger than the true values and are, thus, conservative.

Differential expression of Rel family members in human T-cell leukemia virus type I-infected cells: transcriptional activation of c-rel by Tax protein

The Tax protein of the human T-cell leukemia virus type I (HTLV-I) has been shown to induce nuclear expression of Rel family NF-kappa B-binding proteins. However, under different experimental conditions, different J. H. Kim, Y. Daitoku, and W. G. Greene, J. Virol. 65:6892-6899, 1991). In this study, using specific immunological reagents capable of distinguishing individual members of the Rel family proteins, we show that only c-Rel, not NF-kappa B p50 or p65, is induced in HTLV-I-infected cells. Preferential c-rel induction by HTLV-I infection was detected at the protein and RNA levels as well as in the nuclear NF-kappa B-binding form. Induced c-rel expression was also detected in cells stably transfected with tax cDNA, further correlating the c-rel induction with viral Tax expression. An increase in c-rel mRNA was detected within 3 h after induction of Tax expression, suggesting that this effect is at least partially regulated at the level of transcription. Furthermore, using a particle bombardment method for gene cotransfection, we show that Tax can transcriptionally activate the c-rel promoter in a T-cell line, Jurkat.

Detection of c-mos proto-oncogene expression in human cells

Although the human c-mos proto-oncogene has been characterized for more than a decade, very little is known about its protein product and its expression in somatic cells. We generated three human c-mos-specific antisera and report here the detection of c-mos protein in a human neuroblastoma cell line, SK-N-BE2 (BE2). Both Western (immuno-) blot and immunoprecipitation analyses detected a p37 as the major form and p40 and p35 as minor forms of the c-mos protein. Using Northern blot analysis, 3.5- and 1.7-kb c-mos messages were detected. Using a highly sensitive method that combines reverse transcription and the polymerase chain reaction (RT-PCR), c-mos RNA was detected in all the human samples examined. With Western blot analysis, we further showed that c-mos proteins are expressed in cervical carcinoma-derived cell lines. This ubiquitous expression of low levels of c-mos suggests a fundamental role for the c-mos proto-oncogene.

Similarity of DNA fingerprints due to chance and relatedness

Given the DNA fingerprints of two individuals with some bands being shared by both individuals, we define a new measure of the degree of similarity between the DNA profiles of two individuals. We use this measure to calculate the expected DNA similarity of two unrelated individuals of a randomly mating population; this similarity is due to chance only. Then, the expected similarity between two related individuals is obtained; this similarity is due to chance and relatedness. From these results, the degree of similarity due to relatedness alone may be calculated.

p34cdc2 is physically associated with and phosphorylated by a cdc2-specific tyrosine kinase

The mammalian homologue of the yeast cdc2 gene encodes a 34-kilodalton serine/threonine kinase that is a subunit of M phase-promoting factor. Recent studies have shown that p34cdc2 is also a major tyrosine-phosphorylated protein in HeLa cells and that its phosphotyrosine content is cell cycle regulated and related to its kinase activity. Here, we show that cdc2 is physically associated with and phosphorylated in vitro by a highly specific tyrosine kinase. Tyrosine phosphorylation of cdc2 in vitro occurs at tyrosine 15, the same site that is phosphorylated in vivo. The association between the two kinases takes place in the cytosolic compartment and involves cyclin B-associated cdc2. Evidence is presented that a substantial fraction of cytosolic cdc2 is hypophosphorylated, whereas nuclear cdc2 is hyperphosphorylated. Finally, we show that the tyrosine kinase associated with cdc2 may be a 67-kilodalton protein and is distinct from src, abl, fms, and other previously reported tyrosine kinases.

Information preserving image compression for archiving NMR images

This paper presents a result on information preserving compression of NMR images for the archiving purpose. Both Lynch-Davisson coding and linear predictive coding have been studied. For NMR images of 256 x 256 x 12 resolution, the Lynch-Davisson coding with a block size of 64 as applied to prediction error sequences in the Gray code bit planes of each image gave an average compression ratio of 2.3:1 for 14 testing images. The predictive coding with a third order linear predictor and the Huffman encoding of the prediction error gave an average compression ratio of 3.1:1 for 54 images under test, while the maximum compression ratio achieved was 3.8:1. This result is one step further toward the improvement, albeit small, of the information preserving image compression for medical applications.

A simple method to prepare intact yeast chromosomal DNA for pulsed field gel electrophoresis

Images

Method of path coefficients: a trademark of Sewall Wright

This address is a tribute to a pioneer of population genetics, including human population genetics. The unique methodology employed by Sewall Wright in many genetic problems is the method of path coefficients. This essay traces the historical landmarks in the development of the path method and then shows how some of the conventional statistical results can be converted into expressions involving path coefficients. The construction of a path diagram to represent such statistical results is explained in terms of examples. In the last section an example of applying the path method to the problem of genetic linkage in a random mating population is given. I hope that, despite the ending of the Sewall Wright era, the path method will continue to serve the scientific world.

Classification of plasma cortisol patterns in normal subjects and in Cushing's syndrome

The 24-h pattern of half-hourly sampled plasma cortisol in normal human subjects shows a 24-h (circadian) period, which may be variably distorted in patients who suffer from autonomous hypercortisolism (Cushing's syndrome). We have developed a pattern recognition system for computer classification of cortisol time series into the normal class and subclasses of Cushing's syndrome with different etiology ("pituitary" designating pituitary tumor, "adrenal" designating adrenal tumor, and "ectopic" designating tumor elsewhere). Discriminatory features were extracted from Fourier analysis and Karhunen-Loeve expansion coefficients of cortisol time series. Decision functions were trained by the LMSE algorithm and tested by the jack-knife test procedure on a data-base of 90 normal and patient patterns. The classification accuracy for normal, "pituitary," "adrenal," and "ectopic" classes was 100, 98.1, 98.3, and 100%, respectively. Hence this pattern recognition system may be useful as an aid in the differential diagnosis of Cushing's syndrome.

Genetics of subdivided populations and its relationships with certain measures of association

Unlike inbreeding, population subdivision affects different genotypes differently for multiple alleles, so that the simple relationship between inbreeding and subdivision for two alleles no longer holds for all genotypes. In this communication, the detailed effects of subdivision have been studied for three alleles with results easily generalized to any number of alleles. Then an average effect of subdivision is proposed. This average effect of subdivision is found to play the same role as the inbreeding coefficient for multiple alleles, so that the overall relationship between inbreeding and subdivision may be reestablished again. In the final section, we discuss the relationship of the genetic result with measures of association of square contingency tables arising from epidemiological, social studies, educational and psychological studies.

[A pathological study of primary malignant lymphomas of the thyroid]

Thirty cases of a primary malignant lymphoma (ML) have been studied clinicopathologically and immunohistochemically. The average age of the patients was 59.1 years, and the ratio of males to females was 1:1.7. According to the Kiel classification of MLs, 53.3% had a low grade malignancy and 46.7% were a high grade malignancy. Therefore, the number with a low or a high grade malignancy was almost equal. Most of the low grade malignancies were ML, centroblastic centrocytic, and most of the high grade malignancies were ML, lymphoblastic. From histopathological and immunohistochemical studies, most cases were considered to be of B-cell origin and two thirds of the cases were regarded as being of a follicular center cell origin. Prognosis was better than that of other MLs. Finally, MLs of the thyroid were found combined more frequently with chronic thyroiditis of the Hashimoto type than malignant epithelial neoplasms.

[Changes of creatine phosphokinase and malondialdehyde in the serum and clinical use of large doses of vitamin C following open heart surgery]

The protective effect of a large dose Vit. C on ischemic myocardium was studied on 10 patients who underwent open heart operation and received 250 mg/kg Vit. C before the start of ECC (Group II). Another 10 similar patients receiving no Vit. C served as a control (Group I). Blood samples were taken from the brachial artery at different time intervals for determination of CPK-MB and MDA in both groups. Considerable increases of serum CPK-MB and MDA in both group I and II were noted. The differences of CPK-MB and MDA concentration between Group I and II were highly significant from 2 to 12 hours postoperatively. The effect of Vit. C in the reduction of the release of CPK-MB and MDA after open heart operation was attributed to its action as an oxygen free radical scavenger, thus decreasing the peroxidation of the lipids present in the cell membrane.

[Effect of triptolide on cytokinetics of HeLa cells]

The cytostatic effects of triptolide on HeLa cells in different proliferation stages and cell cycle phases were studied by colony-forming units assay. An exposure of exponential-phase cells to triptolide 0.02-4.00 micrograms/ml for 0.5 h resulted in a biphasic-exponential dose-survival curve (n = 1, D0 = 0.3 micrograms/ml in the most sensitive population; D0 = 2.8 micrograms/ml in the more resistant population). The plateau-phase cells in the same conditions seemed to have lower sensitivity to the drug. The synchronized cells caused by excess TdR double block and the selective detachment of mitotic cells from monolayer were exposed to triptolide 0.06 micrograms/ml for 0.5 h. The sensitivity of cell cycle phases to the drug ranked as follows: S greater than G2, M greater than G1. The result showed that triptolide is one of the cell cycle phase non-specific agents, but more sensitive to S phase cells.

Role of beta-receptor in the radix Angelicae sinensis attenuated hypoxic pulmonary hypertension in rats

Acute pulmonary hypertension was caused by inhalation of 5% O2 in rats. Pulmonary vascular resistance (PVR) increased, but heart rate (HR), cardiac output (CO) and carotid arterial pressure (CAP) were not obviously changed. After an intravenous administration of Radix Angelicae sinensis, the acute pulmonary hypertension induced by inhalation of 5% O2 could be attenuated, but this effect disappeared if propranolol was given before Radix Angelicae sinensis. In chronic experiments, the same results were obtained, but the protective effect of Radix Angelicae sinensis on heart function was not influenced by propranolol. It is suggested that Radix Angelicae sinensis might play a role by stimulating the beta 2-receptor in the prevention of acute and chronic hypoxic pulmonary hypertension. However, prevention of hypertrophy of the right ventricle and enhancement of heart function in chronic hypoxic rats might not be attributed to the beta 1-receptor in the heart.

An expository review of two methods of calculating the paternity probability

There are two methods for calculating the posttests probability of paternity, viz., the nonexclusion probability method (E method) and the paternity index method (lambda method). This report reviews these two methods and explains the reasons behind them, in the hope that it might alleviate the current controversy between the advocates of these two methods. The emphasis throughout the paper is on exposition, using simple examples to illustrate certain principles or properties. A discussion follows the presentation of the two methods. The calculation of the paternity index is based on the genotype (or phenotype) of the accused man; and the value of the paternity index remains the same whether the accusation itself is true or false.

A genetical model for vitiligo

A genetical model is found to provide a good fit to family data on vitiligo. The model postulates that recessive alleles at a set of four unlinked diallelic loci are involved in the causation of the disorder. Under this multiple recessive homozygosis model, for normal X affected families ascertained through the affected parent, the expected segregation probability is .063; the estimated value is 0.53, which is not significantly different from the expected value. For normal X normal families ascertained through an affected offspring, the expected segregation probability is .037; the estimated value is .04.

Pseudo-random mating populations. In celebration of the 80th anniversary of the Hardy-Weinberg law

That random mating leads to Hardy-Weinberg distribution of genotypes is well known. This report is to show that, if the deviations from random mating are of a certain pattern, the offspring generation will also be in Hardy-Weinberg proportions. This brings out the fact that random mating is a sufficient condition, not a necessary one, for the attainment of the Hardy-Weinberg proportions. Such nonrandom-mating populations are tentatively said to be pseudo-random mating. Pseudo-random-mating populations exist for both autosomal and sex-linked systems with two or multiple alleles. This report covers the basic case of a two-allele autosomal locus in detail, but the possible extension to two loci and cytonuclear systems have also been mentioned in discussion.

Hemodynamic and atrial natriuretic peptide responses to fluid removal and reinfusion in hemodialysis patients

The authors have studied the sequential changes in hemodynamic responses and Atrial Natriuretic Peptide (ANP) levels following bicarbonate hemodialysis with fluid removal followed by an infusion of saline and then ultrafiltration of the added fluid. Cardiac output, stroke volume, and thoracic fluid index (TFI) were measured by transthoracic impedence cardiography. Left cardiac work index (LCWI) was derived using these hemodynamic and mean arterial pressure (MAP) measurements. MAP was lower following dialysis when compared to pure ultrafiltration of a similar fluid loss. LCWI decreased during both dialysis and ultrafiltration. TFI, which is inversely related to intrathoracic fluid, increased following dialysis and ultrafiltration. ANP levels fell following fluid removal but remained elevated above normal control levels. The authors conclude that ANP levels are related to fluid not cardiac status in dialysis patients and that impedence cardiography is of value in determining hemodynamic and fluid changes during dialysis.

Identification of the human papillomavirus E2 protein in genital tract tissues

A 27-kilodalton protein representing approximately 60% of the E2 open reading frame of human papillomavirus type 6 (HPV-6) was synthesized in a bacterial expression system. Affinity-purified polyclonal antibody to this protein detected the probable E2 gene product as a 50-kilodalton protein in most condylomas by Western blot (immunoblot) analysis. The E2-positive condylomas were associated with HPV-6, HPV-11, HPV-16, or unidentified HPVs.

A genetical model for emergenesis: in memory of Laurence H. Snyder, 1901-86

When a phenotype is determined by a specific gene combination of several loci, it is called an emergenic trait. Such a trait, although genetically controlled, does not usually run in families, since the specific gene combination can hardly be preserved in the process of reproduction. The present paper suggests a concrete genetical model to account for the phenomenon that there is little resemblance between siblings and parent-child pairs with respect to this trait. The genetical model is multiple homozygosis for all loci involved in the gene configuration. The properties of such a trait in a random mating population for all families, as well as for the segregating families only, are investigated. Some of the difficulties in estimating the genetical parameters on the basis of empirical data are also discussed.

Identification of the human papillomavirus type 6b L1 open reading frame protein in condylomas and corresponding antibodies in human sera

Genital warts (condylomata acuminata) are among the most frequent sexually transmitted infections. Human papillomavirus type 6 (HPV-6), which is etiologically related to a majority of these lesions, has not been propagated in tissue culture. We generated two forms of HPV-6 viral antigens: a chemically synthesized oligopeptide (referred to as the C-terminal synthetic peptide) corresponding to residues 482 to 495 of the 500-amino-acid-long L1 open reading frame (ORF), and a bacterially expressed 54-kilodalton (kDa) fusion protein containing the N-terminal 13 amino acids encoded by the lambda bacteriophage cII gene followed by one vector-insert junctional residue and 462 amino acids of the L1 ORF sequence (residues 39 to 500). The cII-L1 fusion protein was specifically recognized by an antipeptide serum directed against the N-terminal 13 amino acids derived from the cII gene, an antiserum raised against the C-terminal synthetic peptide, and a genus-specific serum prepared by immunization with disrupted viral capsids. The 54-kDa fusion protein was purified, and the sequence of its first 36 amino acids was determined and found to be as predicted by the DNA sequence. Both the genus-specific anticapsid serum and the antiserum raised against the fusion protein identified authentic L1 ORF proteins in HPV-1-induced (58 kDa) and HPV-6/11-induced (56 kDa) papillomas. The synthetic peptide antiserum recognized the 56- to 58-kDa protein in HPV-6-induced warts, but not in HPV-1- or HPV-11-infected specimens. Using the fusion protein as antigen in immunoassays, we were able to detect the corresponding antibodies in human sera.

Estimation of segregation and ascertainment probabilities by discarding the single probands

The first portion of this communication reiterates the method of discarding single probands for studying the segregation ratio under incomplete ascertainment. The organization of the algebra leads to the second portion, in which the "self-contained" subsets are constructed with respect to both the segregation ratio and the ascertainment ratio. These subsets make a more detailed study of segregation and ascertainment possible.

Tests of linkage and heterogeneity in Mendelian diseases using identity by descent scores

When linkage between a recessive Mendelian disease and specific candidate genes is investigated, identity by descent scores in affected sib pairs may be used for tests of linkage and heterogeneity. Statistical tests for performing this analysis are presented. The efficiency and statistical power of the method are also investigated using computer simulations.

An improved technique of radical neck dissection with an analysis of long-term results of 1,000 operated cases of head and neck cancer

An improved technique of radical neck dissection is presented with a report of all 1,000 operated cases of the head and neck region from 1964 to 1980 at the Affiliated Tumor Hospital of Zhongshan Medical College, in Guangzhou, China. The practice has proved that our operative procedures are time-saving, with less blood loss during operation, fewer operative mortalities, fewer complications, better end results, better cosmetic effects, and that the techniques are easier to master.

A method of subdividing genetic data into self-contained subsets

A method of subdividing genetic data into self-contained subsets has been described in terms of examples. The subsets are such that each of them permits a valid estimate of the parameter concerned. Hence, the discarding of one or more subsets would not affect the validity of the remaining data. The detailed statistical properties of such subsets await further investigation. There is a need to simplify the variance formulas for estimates based on partial data.

Basic fallacies in the formulation of the paternity index

Some basic fallacies in the computation of the paternity index have been pointed out. The general finding that the true fathers' mean paternity index is greater than that of nonfathers is a necessary consequence of an algebraic identity, having nothing to do with paternity or nonpaternity. It has also been shown that the paternity index is not a likelihood ratio as claimed. The fact that a paternity index may frequently take values less than unity leads to absurd conclusions regarding the probability of paternity. A formula relating prior and posterior probabilities of paternity, based solely on genetic marker testing results (exclusion or nonexclusion), is reiterated as a substitute for the current paternity index.

Direct detection of the human papovavirus BK in urine of bone marrow transplant recipients: comparison of DNA hybridization with ELISA

Urine specimens from bone marrow transplant (BMT) recipients and from controls were directly tested for BK virus (BKV) DNA sequences by dot hybridization and for BKV antigen by a double-antibody indirect ELISA. A total of 158 specimens from 55 BMT patients (57 collected prior to or at the time of transplantation and 101 in the posttransplant period) and single urines from 125 control subjects were examined by both methods. A molecularly cloned, 32P-labelled BKV probe was hybridized with urine sediments that were spotted directly on nitrocellulose filters and denatured in situ. BKV DNA sequences were detected in 1 (1.8%) pretransplant and 22 (21.8%) posttransplant urines of BMT patients, and in none of control urines. In ELISA of urine supernatants, BKV antigen was detected in 1 (1.8%) pretransplant and 21 (20.8%) posttransplant urines of BMT patients and in 1 (0.8%) of the control urines. The results of the two tests correlated as follows: 16 urines were positive and 253 urines negative by both methods; seven specimens were positive by DNA hybridization only and seven were positive by ELISA alone. Virus excretion in urine was demonstrated in 20 (36.4%) patients by DNA hybridization, in 19 (34.5%) patients by ELISA, in 15 (27.3%) patients by both methods, and in 24 (44%) patients by at least one of the two tests.

Estimating the prior probability of paternity from the results of exclusion tests

A simple method is described for calculating the prior probability of paternity from a series of genetic tests on putative fathers. Two numerical examples have been given to illustrate the method.

Estimation of the marker gene frequency and linkage disequilibrium from conditional marker data

A method is proposed to calculate the maximum likelihood estimate of gene frequency and linkage disequilibrium from disease-codominant marker conditional data. The method is illustrated using data on sickle-cell anemia and Duchenne muscular dystrophy and linked polymorphic restriction endonuclease cleavage sites.

Glycerol transport and phosphorylation by rat hepatocytes

The entry of glycerol into isolated rat hepatocytes appears to be catalyzed by a specific carrier. At a physiological concentration of 0.1 mM, glycerol utilization is rate limited by the permeation step. Intracellular glycerol is trapped by an excess of glycerol kinase, which has a higher apparent affinity for the substrate than that of the membrane carrier. The entry of glycerol into the hepatocytes is highly sensitive to inhibition by monoacetin and cytochalasin B, but not by DL-1,2-propanediol, erythritol, D-glucose, D-galactose, D-mannose, or D-fructose.

Molecular cloning, genomic analysis, and biological properties of rat leukemia virus and the onc sequences of Rasheed rat sarcoma virus

Rasheed rat sarcoma virus (RaSV) has been shown to code for a protein of 29,000 Mr not present in replication-competent rat type C helper virus (RaLV)-infected cells. This protein is a fused gene product consisting of a portion of the RaLV p15 gag protein and the transformation-specific 21,000 Mr (p21) ras protein, which is also found in Harvey murine sarcoma virus. We now report the molecular cloning of both the SD-1 (Sprague-Dawley) strain of RaLV and the transforming ras sequences of RaSV. Heteroduplex analysis of these cloned DNAs demonstrated that the RaSV ras gene (v-Ra-ras) was inserted into the rat type C viral genome with a small deletion of RaLV genetic information in the 5' region of the gag gene and that the v-Ra-ras gene (0.72 kilobase pair) is homologous to and colinear with the p21 ras gene of Harvey murine sarcoma virus (v-Ha-ras). Restriction enzyme mapping confirmed the homology demonstrated by heteroduplex mapping, showing strong site conservation of restriction endonucleases known to cleave v-Ha-ras. Cloned v-Ra-ras DNA transformed NIH 3T3 cells, inducing the synthesis of the p29 RaSVgag-ras protein.

On measuring genetic distance by selection intensity

A simple selection model (fitness 1, w, w2 for AA, Aa, aa) is employed to change the gene frequency of one population to another. The genetic distance is then defined as d = -log w between the two populations. The distance is symmetrical with respect to the two populations. It is additive: d13 = d12 + d23. The sampling variance of d takes a very simple form. The possible difficulties of using genetic distance in studying evolutionary history have been briefly discussed. The writer means no offence to those who have developed or used the various measures of genetic distance.

The selection of a stable rat hepatoma variant with concomitant increase in ploidy and permeability to glycerol

By repeated selection for longer survival in an isotonic solution of glycerol, a stable subline of Novikoff rat hepatoma cells has been isolated. The cells exhibit markedly increased resistances to osmotic lysis in isotonic solutions of glycerol. They are twice as large and have twice as many chromosomes as cells of the parental line. It is suggested that the osmotic stress procedure can be extended for the selection of numerous kinds of mutants and can be used as a method of analysis of membrane properties.

The testing of dominants for heterozygoisty

A simple method of estimating the frequency of heterozygotes among the dominants by test-making has been described; and then a maximum likelihood estimate is obtained by an iterative counting procedure. Eearly results of Haldane have been review and modified. Methods of estimating the gene frequencies, their ratio, and the inbreeding coefficient from test-mating results have also been given.

Membrane-associated enzymes involved in nucleoside processing by plasma membrane vesicles isolated from L929 cells grown in defined medium

adenosine, adenosine,Transport-competent plasma membrane vesicles isolated from a subline of L929 cells (L929se-) grown in serum-free, defined medium accumulate ribose-1-P when exposed to adensoine, inosine, guanosine, or uridine. This observation suggests the action of one or more nucleoside phosphorylases acting prior to, during, or subsequent to the transport event. Extravesicular ribose-1-P neither inhibits uptake nor exchanges with intravesicular ribose-1-P, indicating that the action of the phosphorylase is not prior to uptake. Preloading the vesicles with inosine prior to subjecting the vesicles to conditions under which further uptake could not take place (in the presence of caffeine) did not result in an alteration of the ribose-1-P to inosine ratio within the vesicles. This observation was interpreted as evidence that only exogenously derived, not intravesicular inosine, is the substrate for the nucleoside phosphorylase. This datum, when taken with the fact that hypoxanthine is never found to be a significant extent within the vesicles, suggests that the phosphorolytic cleavage of inosine occurs as a group translocation during the transport itself, so that hypoxanthine is released to the surrounding medium while the ribose-1-P accumulates intravesicularly. Thus, phosphorolysis would seem to occur during passage across the membrane.

Transport mechanisms in isolated plasma membranes. Nucleoside processing by membrane vesicles from mouse fibroblast cells grown in defined medium

Plasma membrane vesicles were isolated from a subline of L929 mouse fibroblasts grown on defined medium in the absence of serum. These vesicles were not significantly contaminated by mitochondria or endoplasmic reticulum. The isolation procedure, a modification of that originally developed by McKeel and Jarett (McKeel, D.W., and Jarett, L. (1970) J. Cell Biol. 44, 417-432) employs mechanical homogenization in isotonic medium followed by differential centrifugation. The resultant plasma membrane vesicles take up radioactivity when exposed to uniformly labeled nucleosides. Two subfractions of the plasma membrane were isolated, distinguished by their differing activity of 5'-nucleotidase and (Na+,K+)-stimulated ATPase, two well known plasma membrane enzyme markers. Uptake of nucleoside radioactivity was extensively studied in one subfraction; it was linear with time and membrane concentration over ranges used for the studies. Apparent Km values for uptake of radioactivity from adenosine, inosine, and uridine were 7.1 +/- 26 muM, respectively. Uptake of radioactivity from all three nucleosides exhibits a broad pH optimum from pH 7 to pH 9, but falls off rapidly at lower pH. N-Ethylmaleimide was an effective inhibitor of uptake of radioactivity from all three nucleosides; uptake of radioactivity from uridine is more sensitive than uptake of radioactivity from the purine nucleosides. Adenosine inhibited uptake of radioactivity from inosine more than from uridine. Inosine inhibited the uptake of radioactivity from adenosine, but uridine did not. Caffeine and 6-methylaminopurine riboside (6-N-methyladenosine differentially inhibit uptake of radioactivity from adenosine and inosine, and thus the vesicles apparently possess seperate transport systems for uptake of radioactivity from purine nucleosides and from uridine.

The existance of a group translocation transport mechanism in animal cells: uptake of the ribose moiety of inosine

After exposure to inosine, transport-competent plasma membrane vesicles isolated from SV-40-transformed Bal/c 3T3 cells accumulate intravesicular ribose 1-PO4 at a concentration 200-fold greater than the extravesicular concentration. An analysis of the purine nucleoside phosphorylase activity distribution in various subcellular fractions, relative to other enzyme activities, indicated the presence of plasma membrane-associated purine nucleoside phosphorylase activity. The plasma membrane vesicles appear relatively impermeable to hypoxanthine. However, hypoxanthine, which is a competitive inhibitor of the transport reaction, is the only compound tested capable of mediating efflux of already accumulated ribose 1-PO4. In addition, hypoxanthine does not result in the efflux of transported uridine which is accumulated in these membrane vesicles as uridine. Exogenous ribose 1-PO4 neither results in counterflow nor does it inhibit the original uptake reaction. The following transport reaction is proposed: uptake occurs by group translocation, mediated by membrane-localized purine nucleoside phosphorylase. The data are consistent with sites for inosine and hypoxanthine being on the outer membrane surface whereas the ribose 1-PO4 site is only on the inner surface.