Regulation of Escherichia coli carbamyl phosphate synthetase. Evidence for overlap of the allosteric nucleotide binding sites

Regulation of Escherichia coli carbamyl phosphate synthetase by UMP and IMP was examined in studies with various analogs of these nucleotides. Whereas UMP inhibits enzyme activity, the arabinose analog of UMP was found to be an activator. dUMP neither activates nor inhibits, but binds to the enzyme in a manner similar to UMP as evaluated by direct binding studies, sedimentation behavior, and ultraviolet difference spectral measurements. dUMP decreases inhibition by UMP and activation by IMP, but has no effect on activation by L-ornithine. The findings are in accord with the view that IMP and UMP bind to the same region of the enzyme; a possible general model for such overlapping binding sites is considered. Additional evidence is presented that inorganic phosphate can modulate regulation of the activity by nucleotides. Phosphate (and arsenate) markedly increase inhibition by UMP, decrease activation by IMP, but do not affect activation by L-ornithine. The extent of activation by IMP and by L-ornithine and that of inhibition by UMP are decreased when Mg2+ concentrations are increased relative to a fixed concentration of ATP. The findings suggest that the allosteric effectors may affect affinity of the enzyme for divalent metal ions as well as, as previously shown, the affinity of the enzyme for Mg-ATP.

Successful treatment of male infertility caused by antispermatozoal antibodies

Spermatozoa in the ejaculate of a man with antispermatozoal antibodies in the serum (gelatin agglutination technique (GAT) titre, 640) and the seminal plasma (GAT titre, 80) were shown to have IgG and IgA bound to them. In preparation for intrauterine artificial insemination, the ejaculate was collected in Tyrode's medium. Then spermatozoa were washed, resuspended in Tyrode's medium, and 0.2 mL of the suspension was injected in the uterus. A successful pregnancy resulted. Reasons are given for considering that the successful pregnancy resulted from the manipulation of the semen.

Intracellular cysteine delivery system that protects against toxicity by promoting glutathione synthesis

Depletion of glutathione by inhibition of its synthesis by buthionine sulfoximine, an irreversible inhibitor of gamma-glutamylcysteine synthetase, leads to increased sensitivity to (i) irradiation and (ii) oxidative stress. In the present work, an intracellular cysteine delivery system was used to promote glutathione synthesis, and this was found to protect against toxicity. Thus, administration of L-2-oxothiazolidine-4-carboxylate protected against acetaminophen toxicity in mice; the thiazolidine, which is converted to L-cysteine by the enzyme 5-oxo-L-prolinase (present in many animal tissues and in plants) promotes the synthesis of glutathione, which is the actual protectant. The effect of this thiazolidine in increasing the level of glutathione is prevented by administration of buthionine sulfoximine. This thiazolidine may be useful in the treatment of other toxicities and in the treatment of certain diseases. It may also be valuable as a component of amino acid mixtures used in therapy and as a safener in agriculture.

Partial characterization of human spermatozoal phosphodiesterase and adenylate cyclase and the effect of steroids on their activities

In sonicated human spermatozoa, phosphodiesterase hydrolyzed adenosine 3':5'-monophosphate (cAMP) at 20.80 +/- 3.23 nmoles/10(8)sperm/20 min at 37 degrees C (50 microM cAMP, initially). In human semen, about 60% of the phosphodiesterase activity was in the spermatozoa. Both polyacrylamide gel electrophoresis and DEAE-cellulose column chromatography indicated that there are at least 5 isozymes of phosphodiesterase. Various steroids were tested at a concentration of 2 micrograms/ml for their effects on phosphodiesterase activity in semen. None was found to have any significant effect. In sonicated human spermatozoa, adenylate cyclase synthesized cAMP at 0.02-2.11 nmoles/10(8)sperm/20 min at 37 degrees C (1 mM ATP, initially) depending on the availability of Mn2+ and caffeine in the assay mixture. Mn2+ was demonstrated to be a potent adenylate cyclase activator in human spermatozoa and its effect on human sperm adenylate cyclase was found to be dose-dependent. Cholera toxin, at a concentration of 20 micrograms/ml, had no effect on human sperm adenylate cyclase activity after it had been incubated with the intact spermatozoa for between 5 min and 5 h at 37 degrees C before the sperm were homogenized and the rate of cAMP formation assayed. In addition, human sperm adenylate cyclase decayed rapidly at 37 degrees C. Of various steroids tested at a concentration of 2 micrograms/ml for their effects on human sperm adenylate cyclase activity, only oestradiol-17 beta showed a significant effect, elevating the rate of cAMP formation by about 30%.

Partial purification of components from fasting human blood serum which stimulate the forward migration of human spermatozoa

Components from fasting human serum that could stimulate the forward migration of human spermatozoa were isolated by gel filtration on Sephadex G-25. The results suggest that these components may be used to enhance sperm forward migration and, hence, pregnancy rate in artificial insemination with husband's semen. (AIH) especially in cases where the sperm forward migration is not optimal.

Effect of cAMP, Mn2+, and phosphodiesterase inhibitors on human sperm motility

The effects of cyclic adenosine monophosphate (cAMP), MnCl2, caffeine, and theophylline at concentrations of 10 mM on human sperm motility and forward migration in vitro were tested. cAMP was effective in activating human spermatozoal motility and forward migration after incubation with the spermatozoa for 3 hr or more and 5 hr, respectively, whereas caffeine and theophylline were effective in activating sperm motility after incubation with the spermatozoa for 1 hr or more. Caffeine and theophylline significantly activated sperm forward migration only after incubation with the sperm for 5 hr. MnCl2, a potent sperm adenylate cyclase activator, had no significant effect in improving human sperm motility and forward migration.

Effects of steroids on the in vitro forward migration of human spermatozoa

The effects of 14 steroids at concentrations between 0.1 and 10 micrograms/ml on human spermatozoal forward migration in vitro were tested. Oestradiol-17 beta at a concentration of 0.1 microgram/ml significantly activated spermatozoal forward migration in ejaculated human semen. However, the effect of oestradiol-17 beta at concentrations of 2 and 10 micrograms/ml on ejaculated human sperm motility was not significantly different from the control where no steroid was added. Progesterone, testosterone, oestriol, oestrone, oestradiol-17d, and ethinyl oestradiol significantly inhibited human spermatozoal forward migration at concentrations of 10 micrograms/ml. Chlormadinone acetate and medroxyprogesterone acetate at concentrations of 2 and 10 micrograms/ml significantly inhibited human spermatozoal forward migration, while norethynodrel, ethynodiol diacetate, norgestrel and lynoestrenol significantly inhibited human spermatozoal forward migration at concentrations between 0.1 and 10 micrograms/ml. However, norethindrone had no demonstrable effect on human spermatozoal forward migration at the above concentrations.

Conversion of UMP, an allosteric inhibitor of carbamyl phosphate synthetase, to an activator by modification of the UMP ribose moiety

UMP is known to be an allosteric inhibitor of carbamyl phosphate synthetase, whereas IMP activates the enzyme. Surprisingly, dialdehyde UMP (prepared by periodate oxidation of UMP) was found to be a potent activator of the enzyme. Dialdehyde IMP, like IMP, produced activation. The corresponding dialcohol analogs of UMP and IMP (prepared by borohydride reduction of the dialdehyde analogs) had no effect on activity. These nucleotide interactions were further characterized by sedimentation velocity studies and by examination of the effects of inorganic phosphate on enzymatic activity. Although UMP promotes formation of an enzyme dimer, and IMP promotes formation of a tetramer (Powers, S. G., Meister, A., and Haschemeyer, R. H. (1980) J. Biol. Chem. 255, 1554-1558), the dialdehyde analogs of UMP and IMP both promote formation of mixed species. Low levels (less than 10 mM) of inorganic phosphate decrease the extent of activation by IMP, dialdehyde IMP, and dialdehyde UMP, but increase the extent of inhibition by UMP. The marked activation observed with dialdehyde UMP, and other considerations, suggest that the binding sites on the enzyme for IMP and UMP may overlap substantially. The findings also suggest that physiological levels of inorganic phosphate function in the modulation of the allosteric regulation of this enzyme by nucleotides.

The binding of oestradiol-17beta to human spermatozoa - an electron microscope autoradiographic study

The location of steroid binding sites with specificity for oestradiol-17beta at an ultrastructural level has been examined on human spermatozoa by electron microscope autoradiography. About 75% of the 438 gains produced by 3H-oestradiol-17beta, and counted on electron microscope autoradiographs, were found over the plasma membrane or within 1000 A of it. This study provides evidence suggesting that the plasma membrane is a site of action of oestradiol-17beta in human spermatozoa.

The binding of sex steroids to human spermatozoa. An autoradiographic study

The locations of steroid binding sites with specificities for 17 beta-oestradiol, progesterone and testosterone have been examined on human spermatozoa by autoradiography. The binding sites were not evenly distributed over the entire surface of human spermatozoa. They were more densely located on the midpiece of the tail, less on the head and neck, and least on the principal- and end pieces of the tail. The binding sites for 17 beta-oestradiol were specific, with 3H-17 beta-oestradiol being displayed by unlabelled 17 beta-oestradiol, but less readily displaced by either progesterone or testosterone. The binding sites for testosterone were less specific than those for 17 beta-oestradiol or those for progesterone. Both 17 beta-oestradiol and progesterone were good competitors for testosterone binding sites, while the binding of 3H-progesterone was easily displaced by 17 beta-oestradiol, but less readily displayed by testosterone. Since there was preferential binding of these steroids to the mid-piece, and strong competition for binding between 17 beta-oestradiol and progesterone, these studies appear to provide information on the sites of action for the reported effects of these and related steroids on spermatozoal motility, migration and metabolism.

An initial step in the induction of cancer, the loss of histone H1 from chromosomes - a hypothesis

Unexpected blood group antigens of the P and ABO blood group systems have been found on gastric carcinoma cells of some individuals whose red cells did not possess the antigens and whose sera contained the corresponding antibodies. On the basis of the known biosynthetic pathways leading to the synthesis of the antigens, and on the concept that the blood group genes involved control the structure of glycosyltransferases, it seems that the individuals possess the respective glycosyltransferases structural genes which are not expressed in normal tissues. However, the genes have become expressed in the carcinoma cells.

Activation of spermatozoal forward migration in vitro by hydrocortisone

The effects of hydrocortisone and cortisone on spermatozoal motility in vitro were tested Hydrocortisone at concentrations of 50, 100 and 1000 nmoles/ml was effective in activating in vitro the forward migration and the motility of boar spermatozoa recovered from the cauda epididymidis. Where boar epididymal spermatozoa were incubated with hydrocortisone at concentrations of 50, 100 and 1000 nmoles/ml for between 0 and 24 h at 25 degrees C in vitro, the spermatozoal motility was significantly higher than where no hydrocortisone was added. With ejaculated boar spermatozoa, hydrocortisone at concentrations of 100 and 1000 nmoles/ml increased the spermatozoal motility for between 0 and 2 h and at concentration of 50 nmoles/ml increased spermatozoal motility for between 2 and 24 hr at 25 degrees C in vitro. After 4 incubation, the effect of hydrocortisone at a concentration of 100 nmoles/ml on boar ejaculated sperm motility was not significantly different from the control. But, hydrocortisone at a concentration of 1000 nmoles/ml inhibited for forward migration of boar ejaculated sperm after it had been incubated with the sperm for 6 h. Cortisone, although structurally similar to hydrocortisone, had no significant effect in improving the motility of boar spermatozoa. Both hydrocortisone and cortisone had no demonstrable effect on the forward migration and the motility of human spermatozoa in vitro.

DR typing in Australian Aborigines. An indication for a second locus in the HLA--D region defined by serology

A group of 43 Australian Aborigines was typed for HLA--DR determinants and other antigens on B cells, using pregnancy sera from Caucasoid women. The group could not be considered as random, since a selection was made for an equal number of Au antigen positive and Au antigen negative individuals The typing results showed that the specificities DRw2, 4 and 8 were as well defined in this population as in Caucasoids, whereas the specificities DRw1, 3, 5 and 7 could not be defined. Even more interesting was the finding that a cluster of six sera, defining the local B cell specificity LB12, gave positive reactions in 41 out of 43 Aborigines. Although LB12 is found to be highly associated with DRw1, 2 and 6 in the Caucasoid population, in 36 cases the LB12 positive Aborigines could not be demonstrated to carry the specificities DRw1 or 2. The recognition of DRw6 is difficult at the moment and for the reason its presence or absence in this material is uncertain. However, three individuals typed positive for DRw4 and 8 and for LB12 as well. These findings strongly support the hypothesis that the genes coding for LB12 and its postulated allele LB13 are separate from the genes coding for the known DR determinants. LB12 is very likely identical to the recently described determinants DC1 (Tosi & Tanigaki 1979) and MB1 (Duquesnoy et al. 1979a).

Correlation between mixed lymphocyte culture and phytohaemagglutinin stimulation responses of human lymphocytes

In fifty-seven healthy individuals a significant correlation ( r = 0.3, P < 0.05) has been found between responses of their lymphocytes to stimulation by PHA and by pooled lymphocytes in MLC. It is suggested that these tests quantitate the general status of T cell reactivity of individuals, and may be used in conjunction with the results of other tests for T cell parameters, in a transplant programme to predict favourable outcome and to monitor immunosuppressive therapy.

Further characterization of the nonimmunoglobulin sperm-agglutinin found in some human sera

A comparison is made between some properties of immunoglobulin and nonimmunoglobulin sperm-agglutinins. It is found that antisperm antibodies are directed against spermatozoal components and bind equally well to viable and nonviable spermatozoa. On the other hand nonimmunoglobulin sperm-agglutinins are directed at both spermatozoal and seminal plasma components and bind to viable sperm. beta-lipoprotein may not be involved in the nonimmunoglobulin sperm-agglutinin found in human sera.

Mixed-lymphocyte culture response in a related and an unrelated Australian population

In 256 related combinations in an Australian Caucasian population, the relative responses in one-way mixed-lymphocyte cultures can be divided into four different groups: (i) HLA zero-haplotype different; (ii) HLA-D homozygous-versus-heterozygous; (iii) HLA one-haplotype different: and (iv) HLA two-haplotype different. The median relative responses of the groups were 0.78%, 20%, 64% and 86.5%, respectively; 17.7% of HLA-A, HLA-B identical siblings were found to stimulate significantly in mixed-lymphocyte culture, and 6.3% of HLA one-haplotype different combinations had weak responses. The median relative response of 225 unrelated random combinations was 100%. One mixed-lymphocyte culture combination in this group gave a relative response of 20%, which was found to be a HLA-D homozygous-versus-heterozygous response. A relative response of 20% in mixed-lymphocyte cultures may be taken to indicate relative HLA-D compatibility and would, therefore, predict a favourable outcome in kidney transplantation. The use of mixed-lymphocyte cultures as a routine in selecting suitable donors in living related transplants and, retrospectively, in monitoring the results of cadaveric transplants, is advocated.