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J Gutknecht

Publications and source records attributed to J Gutknecht.

At least 19 recordsLinked to original sources
PubMed1992

Aspirin, acetaminophen and proton transport through phospholipid bilayers and mitochondrial membranes.

Mechanisms of proton transport were investigated in planar phospholipid bilayer membranes exposed to aspirin (acetylsalicylic acid), acetaminophen (4-acetamidophenol), benzoic acid and three aspirin metabolites (salicylic acid, gentisic acid and salicyluric acid). The objectives were to characterize the conductances and permeabilities of these weak acids in lipid bilayer membranes and then predict their effects on mitochondrial membranes. Of the compounds tested only aspirin, benzoate and salicylate caused significant increases in membrane conductance. The conductance was due mainly to proton current at low pH and to weak acid anion current at neutral pH. Analysis of the concentration and pH dependence suggests that these weak acids act as HA-2-type proton carriers when pH approximately pK and as lipid soluble anions at neutral pH. Salicylate is much more potent than aspirin and benzoate because salicylate contains an internal hydrogen bond which delocalizes the negative charge and increases the permeability of the anion. Model calculations for mitochondria suggest that salicylate causes net H+ uptake by a cyclic process of HA influx and A- efflux. This model can explain the salicylate-induced uncoupling and swelling observed in isolated mitochondria. Since ingested aspirin breaks down rapidly to form salicylate, these results may clarify the mechanisms of aspirin toxicity in humans. The results may also help to explain why the ingestion of aspirin but not acetaminophen is associated with Reye's syndrome, a disease characterized by impaired energy metabolism and mitochondrial swelling.

Acetaminophen↗
PubMed1992

Maintenance of DQB1 polymorphisms in primates.

To understand the evolution of the class II major histocompatibility complex (MHC) DQB1 locus in primates, the second exons of seven DQB1 alleles from five non-human primate species were amplified by polymerase chain reaction. Comparisons of these and other primate sequences show that no between-species diversity is greater than within-species diversity, suggesting maintenance of DQB1 alleles through the history of Old-World primates. There is a preponderance of nonsynonymous nucleotide substitutions at antigen-binding-site codons; this pattern is in marked contrast to what is seen at the closely related, presumably nonfunctional DQB2 gene. The results support the hypothesis that DQB1 polymorphism is maintained by overdominant selection relating to antigen presentation.

Animals↗
PubMed1991

[Severe ischemic hepatitis after taking cibenzoline].

The authors report the case of a 77 year old man suffering from chronic congestive heart failure, who presented a severe hepatic failure. Since 9 days the patient was treated by cibenzoline for serious ventricular arythmias. Hepatic failure was not due to drug hepatotoxicity but to an indirect effect of cibenzoline diminishing cardiac output. Arguments for ischaemic hepatitis and also two mechanisms of hepatic involvement in cardiac diseases are developed. In most cases association of two mechanisms, vascular stasis and low cardiac output is necessary to create hypoxic hepatitis.

Aged↗
PubMed1990

Salicylates and proton transport through lipid bilayer membranes: a model for salicylate-induced uncoupling and swelling in mitochondria.

Mechanisms of proton transport were investigated in phospholipid bilayer membranes exposed to salicylates and benzoates. Membranes were formed from diphytanoyl phosphatidylcholine in decane plus chlorodecane (50% vol/vol). Proton and anion conductances (GH and GA) were calculated from the total conductances and the H+ or A diffusion potentials produced by transmembrane H+ or A gradients. At low pH salicylate caused a GH which was proportional to the square of the total weak acid concentration, and GH was maximum when pH = pK. At neutral to alkaline pH salicylate caused a GA which was proportional to the first power of the salicylate concentration, and GA was independent of pH. Both GH and GA were inhibited by phloretin. The results suggest that salicylate acts as an HA2-type proton carrier at low pH and as a lipid-soluble anion at neutral pH. Salicylate has been implicated as a causal factor in Reye's syndrome, as well as in aspirin poisoning, and salicylate has been reported to increase the proton conductance of inner mitochondrial membranes. The present results suggest that in mitochondria salicylate increases passive proton uptake by a combination of HA influx (driven by the concentration gradient) and A efflux (driven by the voltage and concentration gradients). Model calculations suggest that over the range of therapeutic to toxic concentrations, salicylate causes net H+ influx sufficient to explain the reported "loose coupling," uncoupling and swelling of mitochondria. The relative ineffectiveness of aspirin and benzoate can be explained by their low A permeabilities, whereas the ineffectiveness of 2,6-dihydroxybenzoate can be explained by its low pK.

Anions↗
PubMed1990

The major histocompatibility complex and human evolution.

Many alleles at the human major histocompatibility complex (HLA) loci diverged before the divergence of humans and great apes from a common ancestor. This fact puts a lower limit on the size of the bottleneck in human evolution: the genus Homo must have been founded by no less than ten and probably by more than 10,000 individuals.

Alleles↗
PubMed1990

Evolution of the class II major histocompatibility complex alleles in higher primates.

We have shown that chimpanzees and gorillas have DRB alleles very similar to those of humans. The existence of similar DRB alleles in the different species of higher primates cannot be accounted for by convergent evolution of unrelated alleles that arose independently after the speciation. We therefore conclude that ancestral DRB alleles, that had existed before the speciation, were transmitted to the ancestors of humans, chimpanzees, and gorillas. This conclusion indicates that the diversification of MHC alleles does not start at the inception of a species, but rather proceeds beyond the lifespan of a species. A high degree of sequence similarity found between certain human and non-human primate DRB alleles shows that MHC alleles do not diversify rapidly. The bulk of the contemporary DRB polymorphism seems to have been generated by accumulation of random point mutations during long evolutionary periods preceding the divergence of humans, chimpanzees, and gorillas.

Alleles↗
PubMed1989

Shared class II MHC polymorphisms between humans and chimpanzees.

To gain an insight into the evolution of the major histocompatibility complex alleles, three DRB and one DRA genes were isolated from chimpanzee cDNA libraries. The nucleotide sequences of the chimpanzee DRB (ChLA-DRB) genes were then compared with those of the available HLA-DRB alleles by constructing unrooted phylogenetic trees. All three ChLA-DRB genes were found to be more closely related to certain HLA-DRB alleles than unrelated HLA-DRB alleles are to each other. Since available evidence does not support the convergent evolution of MHC alleles, this result is consistent with the idea that closely related ChLA-DRB and HLA-DRB alleles are derived from common ancestral alleles, the existence of which predates the divergence of human and chimpanzee lineages. The predicted amino acid sequences of mature ChLA-DRA and HLA-DRA molecules differ by only one amino acid.

Amino Acid Sequence↗
PubMed1989

Cloning and mapping of a testis-specific gene with sequence similarity to a sperm-coating glycoprotein gene.

A testis-specific gene Tpx-1, located between Pgk-2 and Mep-1 on mouse chromosome 17, was isolated from a cosmid clone, and its cDNA sequences were determined. The predicted coding sequence of Tpx-1 isolated from BALB/c mice showed 64.2% nucleotide and 55.1% amino acid sequence similarity with that of a rat sperm-coating glycoprotein gene, the protein product of which is secreted by the epididymis. To examine the evolutionary relationship between Tpx-1 and a sperm-coating glycoprotein gene, the cDNA sequence of TPX1, the human counterpart of Tpx-1, was determined. The comparison of the predicted coding sequences of Tpx-1 and TPX1 showed 77.8% nucleotide and 70% amino acid sequence similarity. Since Tpx-1 (from mouse) is more similar to TPX1 (from man) than it is to a rat sperm-coating glycoprotein gene, we conclude that Tpx-1 (TPX1) and a sperm-coating glycoprotein gene are closely related, but distinct, genes belonging to the same gene family. The predicted Tpx-1 protein of a t mutant mouse CRO437 differs from that of BALB/c mice by one amino acid insertion in the putative signal peptide. TPX1 was mapped to 6p21-qter by Southern blot analysis of interspecies somatic hybrid cell lines.

Amino Acid Sequence↗
PubMed1988

Proton conductance caused by long-chain fatty acids in phospholipid bilayer membranes.

Mechanisms of proton conductance (GH) were investigated in phospholipid bilayer membranes containing long-chain fatty acids (lauric, myristic, palmitic, oleic or phytanic). Membranes were formed from diphytanoyl phosphatidylcholine in decane plus chlorodecane (usually 30% vol/vol). Fatty acids were added either to the aqueous phase or to the membrane-forming solution. Proton conductance was calculated from the steady-state total conductance and the H+ diffusion potential produced by a transmembrane pH gradient. Fatty acids caused GH to increase in proportion to the first power of the fatty acid concentration. The GH induced by fatty acids was inhibited by phloretin, low pH and serum albumin. GH was increased by chlorodecane, and the voltage dependence of GH was superlinear. The results suggest that fatty acids act as simple (A- type) proton carriers. The membrane: water partition coefficient (Kp) and adsorption coefficient (beta) were estimated by finding the membrane and aqueous fatty acid concentrations which gave identical values of GH. For palmitic and oleic acids Kp was about 10(5) and beta was about 10(-2) cm. The A- translocation or "flip-flop" rate (ka) was estimated from the value of GH and the fatty acid concentration in the membrane, assuming that A- translocation was the rate limiting step in H+ transport. The kA's were about 10(-4) sec-1, slower than classical weak-acid uncouplers by a factor of 10(5). Although long-chain fatty acids are relatively inefficient H+ carriers, they may cause significant biological H- conductance when present in the membrane at high concentrations, e.g., in ischemia, hypoxia, hormonally induced lipolysis, or certain hereditary disorders, e.g., Refsum's (phytanic acid storage) disease.

Arsenicals↗
PubMed1987

Proton/hydroxide conductance through phospholipid bilayer membranes: effects of phytanic acid.

Mechanisms of proton/hydroxide conductance (GH/OH) were investigated in planar (Mueller-Rudin) bilayer membranes made from decane solutions of phospholipids or phospholipids plus phytanic acid (a 20-carbon, branched chain fatty acid). At neutral pH, membranes made from diphytanoylphosphatidylcholine or bacterial phosphatidylethanolamine had GH/OH values in the range of (2-5) X 10(-9) S X cm-2, corresponding to H+/OH- 'net' permeabilities of about (0.4-1.0) X 10(-5) cm X s-1. GH/OH was inhibited by serum albumin, phloretin, glycerol and low pH, but was increased by chlorodecane and voltage greater than 80 mV. Water permeability and GH/OH were not correlated, suggesting that water and H+/OH- cross the membrane by separate pathways. Addition of phytanic acid to the phospholipids caused an increase in GH/OH which was proportional to the first power of the phytanic acid concentration. In membranes containing phytanic acid, GH/OH was inhibited by albumin, phloretin, glycerol and low pH, but was increased by chlorodecane and voltages greater than 80 mV. The results suggest that phytanic acid acts as a simple (A- type) proton carrier. The qualitative similarities between the behavior of GH/OH in unmodified and phytanic-acid containing membranes suggest that phospholipids may contain weakly acidic contaminants which cause most of GH/OH at pH greater than 4. However, there is also a significant background (pH independent) GH/OH which may be due to hydrogen-bonded water chains. The ability of phytanic acid to act as a proton carrier may help to explain the toxicity of phytanic acid in Refsum's disease, a metabolic disorder in which phytanic acid accumulates to high levels in plasma, cells and tissues.

Cell Membrane Permeability↗
PubMed1987

Proton conductance through phospholipid bilayers: water wires or weak acids?

The proton/hydroxide (H+/OH-) permeability of phospholipid bilayer membranes at neutral pH is at least five orders of magnitude higher than the alkali or halide ion permeability, but the mechanism(s) of H+/OH- transport are unknown. This review describes the characteristics of H+/OH- permeability and conductance through several types of planar phospholipid bilayer membranes. At pH 7, the H+/OH- conductances (GH/OH) range from 2-6 nS cm-2, corresponding to net H+/OH- permeabilities of (0.4-1.7) X 10(-5) cm sec-1. Inhibitors of GH/OH include serum albumin, phloretin, glycerol, and low pH. Enhancers of GH/OH include chlorodecane, fatty acids, gramicidin, and voltages greater than 80 mV. Water permeability and GH/OH are not correlated. The characteristics of GH/OH in fatty acid (weak acid) containing membranes are qualitatively similar to the controls in at least eight different respects. The characteristics of GH/OH in gramicidin (water wire) containing membranes are qualitatively different from the controls in at least four different respects. Thus, the simplest explanation for the data is that GH/OH in unmodified bilayers is due primarily to weakly acidic contaminants which act as proton carriers at physiological pH. However, at low pH or in the presence of inhibitors, a residual GH/OH remains which may be due to water wires, "hydrated defects," or other mechanisms.

Biological Transport↗
PubMed1987

Proton/hydroxide conductance and permeability through phospholipid bilayer membranes.

Proton/hydroxide (H+/OH-) permeability of phospholipid bilayers is several orders of magnitude higher than alkali or halide ion permeabilities at pH 7. The objective of this study was to determine the mechanism(s) of H+/OH- conductance and permeability through planar phospholipid bilayer membranes. Membranes were formed from decane solutions of bacterial phosphatidylethanolamine, diphytanoyl phosphatidylcholine, or egg phosphatidylcholine plus cholesterol. At pH 7, H+/OH- conductance (GH/OH) ranged from 2 to 6 nS.cm-2, corresponding to H+/OH- "net" permeabilities of (0.4-1.6) X 10(-5) cm.sec-1. GH/OH was inhibited by serum albumin (fatty acid-free), phloretin, and low pH. GH/OH was increased by chlorodecane, long-chain fatty acids, and voltages greater than 80 mV. Water permeability and GH/OH were not correlated. The results suggest that the H+/OH- charge carrier (i) is primarily anionic, (ii) crosses the membrane via nonpolar pathway(s), and (iii) can be removed from the membrane by "washing" with serum albumin. The simplest explanation is that the phospholipids contain weakly acidic contaminants that act as proton carriers at neutral pH. However, at low pH or in the presence of inhibitors, a "background" GH/OH remains that may be due to other mechanisms.

Electric Conductivity↗