Salivary peroxidase,Pm, and Ph protein polymorphisms in Malaysians

Summary Three human saliva genetic markers, namely, salivary peroxidase (SAPX), Pm, and Ph proteins, were investigated in the three major ethnic groups of Malaysia: Malays, Chinese, and Indians.For Pm, the allelic frequencies of Pm ⁺ for Malays, Chinese, and Indians are 0.385±0.030, 0.282±0.026, and 0.289±0.026 respectively. For Ph, the allelic frequencies of Ph ⁺ are 0.082±0.016 for Malays, 0.109±0.017 for Chinese, and 0.062±0.013 for Indians. For SAPX, the allelic frequencies of SAPX ¹ in Malays, Chinese, and Indians are 0.762±0.027, 0.755±0.027, and 0.723±0.026 respectively.     

Rare phenotypes of the phosphoglucomutase locus 1 detectable by isoelectric focusing on Cellogel

Summary The rare phenotypes PGM₁, determined by alleles PGM ₃ ¹ , PGM ₄ ¹ , PGM ₆ ¹ , and PGM ₇ ¹ were examined by starch gel electrophoresis and cellulose acetate gel isoelectric focusing and were compared with the commonest phenotypes of PGM₁.The frequencies of the rare genes found in the Polish populations were as follows: in Lublin, PGM ₃ ¹ =0.0002, PGM ₄ ¹ =0.0005, PGM ₆ ¹ =0.0010, and PGM ₇ ¹ =0.0005; in Wroclaw, PGM ₃ ¹ =0.0000, PGM ₄ ¹ =0.0005, PGM ₆ ¹ =0.0007, and PGM ₇ ¹ =0.0002.The results suggest that the F and S type variants of the genes PGM ₄ ¹ and PGM ₇ ¹ probably do not occur. It is still possibile that F and S variants exist for the genes PGM ₃ ¹ and PGM ₆ ¹ .     

Isoelectric focusing of red cell phosphoglucomutase (E.C.:2.7.5.1) at the PGM1 locus in a French-Canadian population

Summary Phosphoglucomutase₁ (PGM₁) polymorphism was studied in a French-Canadian population of Québec city, Canada by means of a low voltage (max 500 V) isoelectric focusing (IEF) procedure on vertical polyacrylamide gel slabs. Frequencies of the four common PGM₁ genes estimated from the phenotype distribution in 308 unrelated individuals were PGM ₁ ¹⁺ , 0.61 (±0.02); PGM ₁ ^1- , 0.13 (±0.01); PGM ₁ ¹⁺ , 0.61 (±0.02); PGM ₁ ^1- , 0.18 (±0.02); and PGM ₁ ¹⁺ , 0.61 (±0.02); PGM ₁ ^1- , 0.08 (±0.01). The segregation patterns observed in 154 families, which included 31 different mating types and 353 children, confirmed a Mendelian inheritance of four autosomal genes. The distribution of the PGM₁ phenotypes observed or expected in a Hardy-Weinberg equilibrium was compared with that of other populations. A significant (P<0.001) difference was found between the Québec population and a Black population from Keneba, Gambia, West-Africa.     

Red cell enzymes of the Pongidae

Summary The red cell enzymes acid phosphatase, adenylate kinase, adenosine deaminase and phosphoglucomutase were analyzed by horizontal starch gel electrophoresis in 43 members of the family Pongidae: Pongo pygmaeus (n=10), Gorilla g. gorilla (n=8), Pan troglodytes (n=22) and Pan paniscus (n=3).In all the Pongidae a red cell acid phosphatase zymogram corresponding to the phenotype B in man was found. The adenylate kinase corresponded to the human phenotype AK 1. All the Pongidae showed the same homozygous adenosine deaminase phenotype which was different from the zymograms in man and was designated ADA ape. In all Pongidae the allele PGM ₁ ¹ was present, in addition in Gorilla g. gorilla a second allele was demonstrated, PGM ₁ ^Go . In Pan troglodytes a second allele, PGM ₁ ^Pan was recognized. In Pongo pygmaeus and Gorilla g. gorilla the PGM₂ patterns differed in their migration rates from PGM₂ 1 in man. In one individual of the species Pan troglodytes a PGM₂ zymogram was found resembling the heterozygous phenotype PGM₂ 3–1, PGM ₂ ¹ PGM ₂ ³, (type Palmer) in man. In all the other individuals of the species Pan troglodytes and in those of the species Pan paniscus the PGM₂ zymogram corresponded to the phenotype PGM₂ 1 in man.

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Zusammenfassung Bei 43 Vertretern der Familie Pongidae, Pongo pygmaeus (n=10), Gorilla g. gorilla (n=8), Pan troglodytes (n=22) und Pan paniscus (n=3), wurden die Erythrocytenenzyme saure Phosphatase, Adenylatkinase, Adenosindeaminase und Phosphoglucomutase mit der horizontalen Stärkegelelektrophorese analysiert. Bei allen Pongiden fanden wir eine saure Phosphatase, die dem Phänotyp B des Menschen entsprach, und eine Adenylatkinase, die dem Phänotyp AK 1 des Menschen glich. Alle Pongiden besaßen das gleiche, einem homozygoten Phänotyp entsprechende Adenosindeaminase-Zymogramm, das sich von den Zymogrammen des Menschen unterschied; wir bezeichnen diesen Phänotyp mit ADA ape. Bei allen Pongiden kommt das Allel PGM ₁ ¹ vor, bei Gorilla g. gorilla zusätzlich ein zweites Allel, PGM ₁ ^Go , und bei Pan troglodytes ein zweites Allel, PGM ₁ ^Pan . Die PGM₂-Zymogramme von Pongo pygmaeus und Gorilla g. gorilla unterschieden sich in ihrer elektrophoretischen Wandergeschwindigkeit vom Phänotyp PGM₂ 1 des Menschen. Bei einem Individuum der Species Pan troglodytes fanden wir ein heterozygotes PGM₂-Zymogramm, das an den heterozygoten Phänotyp PGM₂ 3–1, PGM ₂ ¹ PGM ₂ ³ (Typ Palmer) des Menschen erinnerte, bei allen übrigen Individuen der Species Pan troglodytes und bei denen der Species Pan paniscus ein homozygotes PGM₂-Zymogramm, das dem Phänotyp PGM₂ 1 des Menschen entsprach.

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Supported by the Deutsche Forschungsgemeinschaft.     

Investigation of PGM13, PGM16, and PGM17 variants by isoelectric focussing. Evidence for new subtypes of the PGM 1 3 and PGM 1 7 alleles

Summary A total of 345 haemolysates previously phenotyped by starch gel electrophoresis and known to contain the products of the PGM ₁ ³ , PGM ₁ ⁶ , and PGM ₁ ⁷ alleles have been analyzed by thin layer polyacrylamide gel isoelectric focussing in the pH range 5–7. Two common subtypes, 3+and 3-, of the PGM ₁ ³ allele have been found in a number of Pacific populations. A single form of the PGM ₁ ⁷ allele was observed in the Western Caroline Islands. In contrast, one of two Indian PGM₁7 variants focussed to a different position when compared with the form found at polymorphic frequency in the Western Caroline Islands. Only one type of the PGM ₁ ⁶ allele was detected during the present investigation.     

Polymorphism of erythrocyte phosphoglucomutase,adenylate kinase and adenosine deaminase in northern Thailand

Summary Phenotypes of the erythrocyte enzymes phosphoglucomutase (PGM) (n-587), adenylate kinase (AK) (n=695), and adenosine deaminase (ADA) (n=616) were determined by horizontal starch gel electrophoresis in Thai subjects from norther Thailand, mainly from the provinces of Chiang Mai and Lamphun. The following gene frequencies were calculated: PGM ₁ ¹ 0.7385 PGM ₁ ² 0.2487 PGM ₁ ⁶ 0.0102 PGM ₁ ⁷ 0.0026, AK ¹ 0.9950 AK ² 0.0050, ADA ¹ 0.9180 ADA ² 0.0820.The regular, apparently autosomal transmission of the PGM ₁ ⁶ and PGM ₁ ⁷ alleles was demonstrated in 7 families revealing sufficient data.

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Zusammenfassung Die Phänotypen der Erythrocytenenzyme Phosphoglucomutase (PGM) (n=587), Adenylatkinase (AK) (n=695), and Adenosindeaminase (ADA) (n=616) wurden mittles horizontaler Stärkegelelektrophorese bei Thailändern aus Nordthailand, hauptsächlich aus den Provinzen Chiang Mai und Lamphun, bestimmt. Auf Grund der Ergebnisse wurden die in der englischen Zusammenfassung angegebenen Genfrequenzen berechnet. Die regelmäßige, anschinend autosomale Vererbung der Allele PGM ₁ ⁶ und PGM ₁ ⁷ wurde in 7 Familien mit ausreichenden Daten nachgewiesen.

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Established and supported by Stiftung Volkswagenwerk.     

Crossover of a high-spin (S=7/2, 3/2) to a low-spin (S=1/2) iron-selenium cluster in FA and FB of photosystem I on rebinding of PsaC onto P700-FX cores

 PsaC is a tightly bound ferredoxin in the Photosystem I (PS I) reaction center which contains two [4Fe-4S] clusters named F_A and F_B. We recently proposed that the mixed-ligand F_B cluster in C14D_PsaC and the mixed-ligand F_A cluster in C51D_PsaC exist in a spin state of S=3/2, and that a spin state crossover to S=1/2 occurs when the PsaC mutants are rebound onto P700-F_X cores. Since EPR signals from a highly rhombic S=3/2 spin state can be difficult to study, wild-type PsaC was reconstituted with iron and selenium to introduce an easily detected S=7/2 spin state similar to that shown for Clostridial ferredoxin. When the unbound [4Fe-4Se] PsaC was chemically reduced, a sharp derivative resonance was found at g=5.171 attributed to the excited ±3/2 doublet from an S=7/2 spin multiplet. An additional peak was found at g=5.616 attributed to the superimposed ±1/2 and ±3/2 doublets from a highly rhombic S=3/2 spin multiplet, and an axial set of resonances found around g=2.0 attributed, in part, to a classical S=1/2 spin state. When the [4Fe-4Se] PsaC was rebound onto P700-F_X cores, the spin population derived from the S=7/2 and 3/2 spin states was negligible. Illumination of the rebuilt PS I complex at 15 K resulted in two rhombic sets of resonances, one with g values of 2.043, 1.941 and 1.854, diagnostic of F_A, and the other with g values of 2.067, 1.941 and 1.878, diagnostic of F_B. Chemical reduction with sodium dithionite at pH 10.5 or photoaccumulation by freezing during illumination resulted in a set of resonances with g values of 2.046, 1.938, 1.920 and 1.883, characteristic of a spin-coupled F_A ^–/F_B ^– pair. The spin state crossover in this iron chalcogenide cluster is the first known to be induced by protein-protein association and reinforces the hypothesis that an S=3/2 to 1/2 crossover occurs in the PS I-rebound mutants C14D_PsaC and C51D_PsaC. Received: 6 August 1996 / Accepted: 28 December 1996     

Arterial hypoxemia and performance during intense exercise

In order to determine the level of hypoxemia which is sufficient to impair maximal performance, seven well-trained male cyclists [maximum oxygen consumption (VO_2max)51·min^–1 or 60 ml·kg^–1·min^–1] performed a 5-min performance cycle test to exhaustion at maximal intensity as controlled by the subject, under three experimental conditions: normoxemia [percentage of arterial oxyhemoglobin saturation (%S _a O₂)>94%], and artificially induced mild (%S _aO₂=90±1%) and moderate (%S _aO₂=87±1%) hypoxemia. Performance, evaluated as the total work output (Work_tot) performed in the 5-min cycle test, progressively decreased with decreasing %S _aO₂ [mean (SE) Work_tot=107.40 (4.5) kJ, 104.07 (5.6) kJ, and 102.52 (4.7) kJ, under normoxemia, mild, and moderate hypoxemia, respectively]. However, only performance in the moderate hypoxemia condition was significantly different than in normoxemia (P=0.02). Mean oxygen consumption and heart rate were similar in the three conditions (P=0.18 andP=0.95, respectively). End-tidal partial pressure of CO₂ was significantly lower (P=0.005) during moderate hypoxemia compared with normoxemia, and ventilatory equivalent of CO₂ was significantly higher (P=0.005) in both hypoxemic conditions when compared with normoxemia. It is concluded that maximal performance capacity is significantly impaired in highly trained cyclists working under an %S _aO₂ level of 87% but not under a milder desaturation level of 90%.     

Acyl-CoA: cholesterol acyltransferase-2 gene polymorphisms and their association with plasma lipids and coronary artery disease risks

Acyl-CoA: cholesterol acyltransferase-2 (ACAT2), an intracellular cholesterol esterification enzyme found only in the intestine and liver, has been demonstrated to be associated with hypercholesterolemia and atherosclerosis in mice. To explore the possible impact of ACAT2 gene variants on CAD susceptibility and plasma lipid levels, three polymorphisms, 41A>G (Glu>Gly), 734C>T (Thr>Ile), and IVS4-57_58 ins48 bp (D/I), were genotyped in 809 CAD patients (CAD+) and 1,304 controls (CAD−) from three distinct Singaporean ethnic groups (1,228 Chinese, 367 Malays and 518 Indians). The 734T allele frequency was significantly lower in CAD+ (0.20) than CAD− (0.26) in Chinese (P=0.003) and I allele of D/I was significantly higher in CAD+ (0.17) than CAD− (0.10) in Indians (P=0.011). The 41G allele was significantly more frequent among normolipidemic (0.19) than dyslipidemic (0.13) individuals in Chinese (P=0.008). In normolipidemic females, 734C>T was associated with apoA1, apoB and lipoprotein (a) in Indians, and with apoA1 in Malays, whereas 41A>G is associated with total cholesterol in Indians. The 734C>T polymorphism was in almost complete linkage disequilibrium (LD) with the IVS4-57_58 ins48 bp and in very strong LD with 41A>G in all the three ethnic groups. In the normolipidemic females, the AG/CT had much higher apoB than AA/CC in Indians. We found that the three ACAT2 polymorphisms studied are associated with CAD risk and plasma lipid levels but their effects are not consistent across genders and ethnic groups.     

Restriction and persistence of polymorphisms of HLA and other blood genetic traits in the Parakanã Indians of Brazil

Results concerning HLA types and 22 other blood genetic systems are reported for the Parakanã Indians of northern Brazil, a tribe that is notable for the light color and pilosity of some of its members. No clear evidence of Caucasoid admixture was found, but the Parkanã show unusual frequencies in the EsD¹, PGM¹₁, Gc², Cp^B, Fy^a, Di^a, and L^M genetic markers. In addition, the very rare Rh allele r^y is present, as well as what seems to be a new PGM₂ variant. There is very limited heterogeneity in the HLA system. All these distinctive features may have arisen through a combination of founder effects and genetic drift. However, low F_is values, as well as higher mean ages in heterozygous as compared to homozygous persons, suggest that an heterotic effect is counteracting these dispersive forces.     

Isoelectric focusing of human red cell phosphoglucomutase (PGM1). Phenotype distribution in the population of Tuscany and two hereditary variants

Summary Phosphoglucomutase (PGM₁) phenotypes were determined in a population sample of Tuscany, Italy, by isoelectric focusing. The frequencies observed for the four alleles are: PGM ₁ ¹⁺ =0.6012, PGM ₁ ^1- =0.1059, PGM ₁ ²⁺ =0.2495, PGM ₁ ^2- =0.0434. Two variants were detected and it was possible to study the parentage of both of them. The pedigree of the propositus of the first variant shows that the variant occurs in combination with the common alleles PGM₁ 1+ and PGM₁ 2+ and that it has an autosomal dominant inheritance. The second variant has been shown to be a product of the PGM₂ locus, although its PAGIF pattern is included between 2- and 1+ isoenzymes.     

Effects of various metabolites on two phosphoglucomutase allozyme activities from Drosophila melanogaster

The effects of various metabolites on the two most common phosphoglucomutase allozymes (PGM^A and PGM^B) in Drosophila melanogaster have been investigated in vitro. 2,3-Diphosphoglycerate (2,3DPG) inhibited PGM^A and PGM^B to the same degree in the presence of 25 µM glucose-1,6-diphosphate (G1, 6P₂). However a higher concentration of G1,6P₂ partially reversed the inhibition of PGM^A exerted by 2,3DPG, so that in the presence of 150 µM G1,6P₂ the inhibition of PGM^A was half that of PGM^B at pH 6.0. Glycerol-3-phosphate (G3P) had no significant effect at pH 7.4 but exerted an activating effect at pH 6.0 which was more pronounced in the case of PGM^B. ATP, citrate, and fructose-1, 6-diphosphate (F1,6P₂) inhibited both PGM^A and PGM^B. The differences found in vitro between these two allozymes can have a significant impact on in vivo function and, therefore, on the maintenance of PGM polymorphism in experimental populations of D. melanogaster studied in the laboratory.     

Human mitochondrial glutamic-oxaloacetic-transaminase,GOTM: Formal genetics

Summary The polymorphism of human GOT_M was investigated in red blood cells by means of routine starch gel electrophoresis. The formal model of two common alleles, GOT _M ¹ and GOT _M ² , at an autosomal locus GOT_M was confirmed by examination of 640 mother-child pairs. The frequency of GOT _M ¹ in this sample from southwestern Germany was calculated to be 0.981±0.003.     

Thermoregulation in three species of Afrotropical subterranean mole-rats (Rodentia: Bathyergidae) from Zambia and Angola and scaling within the genus Cryptomys

The thermoregulatory characteristics of three species of Cryptomys from Zambia and Angola are examined and, together with published data on four other species of Cryptomys from southern Africa, used to determine whether scaling occurs in this genus of subterranean rodents. The thermoregulatory properties of acclimated giant Zambian mole-rats, Cryptomys mechowi ( =267 g), Angolan mole-rats, Cryptomys bocagei ( =94 g) and Zambian common mole-rats Cryptomys hottentotus amatus ( =77 g) are as follows. Mean resting metabolic rates (RMRs) within the respective thermoneutral zones were 0.60±0.08 cm³ O₂ g^-1 h^-1 (n=12) for C. mechowi; 0.74±0.06 cm³ O₂ g^-1 h^-1 (n=8) for C. bocagei and 0.63±0.06 cm³O₂ g^-1 h^-1 (n=21) for C. h. amatus. The thermoneutral zones (TNZs) of all three species are narrow: 29–30°C for C. mechowi; 31.5–32.5°C for C. bocagei and 28–32° C for C. h. amatus. The increase in mean RMR at the lowest temperatures tested (15° C for C. mechowi, 18° C for C. bocagei and C. h. amatus) was 2.35, 2.2 and 3.82 times their RMR in the TNZ respectively. Body temperatures are low, 34±0.53° C (n=24) for C. mechowi, 33.7±0.32° C (n=20) for C. bocagei and 33.8±0.43° C (n=40) for C. h amatus. At the lower limit of thermoneutrality, conductances are 0.09±0.01 cm³ O₂ g^-1 h^-1 °C^-1 (n=30) in C. mechowi; 0.12±0.01 cm³ O₂ g^-1 h^-1 °C^-1 (n=20) in C. bocagei and 0.12±0.03 cm³ O₂ g^-1 h^-1 °C^-1 (n=32) in C. h. amatus. The range in mean body mass among the seven species of Cryptomys examined for scaling was 60 g (C. darlingi) to 267 g (C. mechowi). There is no clear relationship between RMR within the TNZ and body mass. The resultant relationship is represented by the power curve RMR=2.45 mass^-0.259.     

Introgression of group 4 and 7 chromosomes of <Emphasis Type="Italic">Ae</Emphasis>. <Emphasis Type="Italic">peregrina</Emphasis> in wheat enhances grain iron and zinc density

Dietary deficiency of iron and zinc micronutrients affects more than two billion people worldwide. Breeding for micronutrient-dense crops is the most sustainable and cost-effective approach for alleviation of micronutrient malnutrition. Three accessions of Aegilops peregrina (Hack.) Maire & Weill (2n = 28, U^PU^PS^PS^P), selected for high grain iron and zinc concentration were crossed with Triticum aestivum L. cv. Chinese Spring (Ph ^I ). The sterile F₁ hybrids were backcrossed with elite wheat cultivars to get fertile BC₂F₂ derivatives. Some of the fertile BC₂F₂ derivatives showed nearly 100% increase in grain iron and more than 200% increase in grain zinc concentration compared to the recipient wheat cultivars. The development of derivatives with significantly higher grain micronutrients, high thousand-grain weight and harvest index suggests that the enhanced micronutrient concentration is due to the distinct genetic system of Ae. peregrina and not to the concentration effect. Genomic in situ hybridization, comparison of introgressed chromosomes with the standard karyotype of Ae. peregrina and simple sequence repeat marker analysis revealed the introgression of 7S^P chromosomes in five selected derivatives, 7U^P in four, group 4 and 4S^P in three and a translocated 5U^P of Ae. peregrina in one of the selected derivatives. Molecular marker analysis using the introgressed chromosome markers indicated that two of the BC₂F₃ progenies were stabilized as disomic addition lines. It could, therefore, be concluded that the group 4 and 7 chromosomes of Ae. peregrina carry the genes for high grain iron and zinc concentration.     

Frequency dependent selection: I. Rare male phenomenon in D. subobscura dependent on the proportion of Amy genotypes and substrate composition

Analysis of the rare male mating advantage in D. subobscura, as a type of frequency dependent selection on maltose and starch media, was done by applying different statistical approaches (χ², cross-product ratio, variance and regression analysis). They reveal that mating occurs at random when proportions of prospective mates are equal, and that mating success of the males homozygous for Amy-locus genotypes (S/S and F/F) depends on their proportion. Regression analysis showed that the F/F males are sexually more active (have higher vigour) than S/S males. Rare male effect is one-sided and appears in F/F males that partake in more heterogamic matings. Comparison of the number of observed and expected homo- and heterogamic matings shows that homogamic matings are more frequent. Multifactorial analysis of variance shows that the number of matings are different for nine pairs of lines and four possible mating types (S_fS_m, S_fF_m, F_fS_m, F_fF_m). The rare male phenomenon is not dependent on different food composition, but is associated with variations in individual genotypes.     

Genetic control of several α-amylase isozymes in winter hexaploid wheat

α-Amylase isozymes were detected via electrophoretic separation in a Tris-glycine polyacrylamide gel system (pH 8.4). Three chromosome 6B loci controlling the α-amylase isozyme composition were identified by studying the grain α-amylase patterns in an F_→∞ self-pollinating population of winter common wheat (Donskoi Mayak). The loci were found to take the following order in the long arm of chromosome 6B: cen. cen.—α-Amy-B3—α-Amy-B6—α-Amy-B1     

A spectroscopic model for the high pH form of sulfite oxidase

The syntheses and spectroscopic properties of two monomeric oxo-Mo(V) complexes [NMe₄][MoO(SC₆H₄---CH=N---C₆H₄O)(SAr)₂] (Ar=Ph (2a), PhCH₃ (2b)) exhibiting a novel S₃NO coordination site are described. The EPR parameters of the Mo(V) complexes are almost identical with the parameters for the high pH form of sulfite oxidase, allowing further predictions for the unknown coordination site of the molybdenum cofactor in such molybdenum-containing enzymes. The Mo(V) compounds react with water to form a μ-oxo-bridged Mo(V) dimer, which is readily oxidized by oxygen to give the monomeric dioxo-Mo(VI) complex MoO₂(SC₆H₄---CH=N---C₆H₄O)(sol) (4) (sol=acetonitrile; dimethyl sulfoxide (DMSO)). The structure of 4 has been determined by X-ray crystallography (space group P (No. 2), a=7.855(4), b=9.530(3), c=11.676(6) Å, α=103.96(3), β=99.03(3), γ=100.73(3)°, V=814.5 ų, ρ_calc=1.79 g cm⁻³, Z=2, R(F)=0.026, R(wF)=0.026). The geometry about the molybdenum is distorted octahedral, with two terminal oxo groups cis to each other.     

Genetic variability in the European minnow,Phoxinus phoxinus (L.)

An electrophoretic study of genetic variation at 11 loci was performedfor a population of European minnows, Phoxinus phoxinus (L.). Ten loci, EST-1 ^*, EST-2 ^* EST-3 ^*,GPD-1 ^*,GPD-2 ^*,GPI-1 ^*,GPI-2 ^*,MPI ^*,6PGD ^* and PGM ^* were polymorphic. IDH ^*wasmonomorphic. The mean number of heterozygotic loci over all 176 fish was 3.05 ± 0.104(SE). Observed mean heterozygosity was 0.28±0.058(SE) and expected mean heterozygosity was 0.27±0.054(SE). EST-2 ^*, EST-3 ^* andPGM ^* were not in Hardy-Weinberg equilibrium. Length,condition, parasite numbers or male breeding characters, i.e. red colorationand tubercles, were not influenced by single enzyme loci.     

Surface charges on the outer side of mollusc neuron membrane

Summary The shifts of current-voltage characteristics of sodium and calcium inward currents produced by changes in the concentration of divalent cations (Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺) and in pH of the extracellular solution have been measured on isolated neurons of the molluscHelix pomatia intracellularly perfused with potassium-free solutions. On the basis of these shifts and using Stern's theory (O. Stern, 1924.Z. Electrochem. 30508–516), the binding constants for the ions to charged groups of the outer side of the somatic membrane and the density of the surface charges produced by these groups have been calculated. For groups located in the vicinity of sodium channels we obtainedK _Ca=90±10,K _Sr=60±10,K _Ba=25±5 andK _Mg=16±5m ^–1 at pH=7.7 and for groups located in the vicinity of calcium channelsK _Ca=67±10,K _Sr=20±5 andK _Ba=19±5m ^–1 at pH=7.0. The same groups bind H⁺ ions with apparent pK=6.2±0.2 that corresponds toK _H=1.6×10⁶ m ^–1. The density of fixed charges near the sodium channels is 0.17±0.05 e/nm² (pH=7.7) and near the calcium channels is 0.23±0.05 electrons/nm² (pH=7.0). From the comparison of the obtained values with the data about binding constants of the same ions to different negatively charged phospholipids, a suggestion is made that just the phophatidylserine is responsible for the surface potential of the outer side of the somatic membrane. It was also shown that the presence of this potential results in a change in the concentration of carrier ions near the membrane which affects the maximal values of the corresponding transmembrane currents.