Glucose-6-phosphate dehydrogenase. Translational regulation of synthesis and regulation of processing of the enzyme in the uterus by estradiol

Non-genomic mechanisms in the estrogen regulation of glycolytic protein levels in endothelial cells

Few studies have explored the mechanisms coupling estrogen signals to metabolic demand in endothelial cells. We recently showed that 17β-estradiol (E2) triggers angiogenesis via the membrane G-protein coupled estrogen receptor (GPER) and the key glycolytic protein PFKFB3 as a downstream effector. We herein investigated whether estrogenic agents regulate the stability and/or degradation of glycolytic proteins in human umbilical vein endothelial cells (HUVECs). Similarly to E2, the GPER selective agonist G1 rapidly increased PFKFB3 protein amounts, without affecting mRNA levels. In the presence of cycloheximide, E2 and G1 treatment counteracted PFKFB3 degradation over time, whereas E2-induced PFKFB3 stabilization was abolished by the GPER antagonist G15. Inhibitors of selective SCF E3 ubiquitin ligase (SMER-3) and proteasome (MG132) rapidly increased PFKFB3 protein levels. Accordingly, ubiquitin-bound PFKFB3 was lower in E2- or G1-treated HUVECs. Both agents increased deubiquitinase USP19 levels through GPER signaling. Notably, USP 19 siRNA decreased PFKFB3 levels and abolished E2- and G1-mediated HUVEC tubularization. Finally, E2 and G1 treatments rapidly enhanced glucose transporter GLUT1 levels via GPER independent of transcriptional activation. These findings provide new evidence on mechanisms coupling estrogen signals with the glycolytic program in endothelium and unravel the role of USP19 as a target of the pro-angiogenic effect of estrogenic agents.

Glucose-6-phosphate dehydrogenase--beyond the realm of red cell biology

Glucose-6-phosphate dehydrogenase (G6PD) is critical to the maintenance of NADPH pool and redox homeostasis. Conventionally, G6PD deficiency has been associated with hemolytic disorders. Most biochemical variants were identified and characterized at molecular level. Recently, a number of studies have shone light on the roles of G6PD in aspects of physiology other than erythrocytic pathophysiology. G6PD deficiency alters the redox homeostasis, and affects dysfunctional cell growth and signaling, anomalous embryonic development, and altered susceptibility to infection. The present article gives a brief review of basic science and clinical findings about G6PD, and covers the latest development in the field. Moreover, how G6PD status alters the susceptibility of the affected individuals to certain degenerative diseases is also discussed.

Stereoisomer-specific inhibition of superoxide anion-induced rat aortic smooth-muscle cell proliferation by 17beta-estradiol is estrogen receptor dependent

An in vitro xanthine/xanthine oxidase reaction system was used to generate superoxide anions that significantly stimulated tritiated [3H]thymidine incorporation into endothelium-removed (denuded) male rat aortic explants. Tritiated thymidine uptake was used as an index of vascular smooth-muscle cell (VSMC) proliferation. Superoxide dismutase (SOD) significantly attenuated the oxygen free radical-induced proliferative response of these cells. 17Beta-estradiol (17beta-E) significantly inhibited superoxide anion-induced VSMC proliferation. In contrast, the growth-modifying effects of 17beta-E were not mimicked by 17alpha-estradiol (17alpha-E), progesterone, or testosterone. The pure estrogen receptor (ER) antagonist, ICI 164,384, reversed the growth-inhibitory effect of 17beta-E. 17Beta-estradiol failed directly to reduce in vitro superoxide anion production or to modify xanthine oxidase activity. Therefore, these data indicate that 17beta-E, through an ER-dependent mechanism, specifically and significantly inhibited superoxide anion-mediated SMC proliferation in denuded rat aortic explants.

Regulation of a uterine 250 kDa protein by estradiol and antiestrogens

A 250 kDa secretory protein was isolated from the uterine luminal fluid (ULF) obtained from estradiol-treated ovariectomized rats. Antiestrogens blocked the production of this protein. The protein components were separated and purified by SDS-PAGE. Polyclonal antibodies were raised against the 250 kDa protein and used to identify the protein by Western blot. 17 beta-estradiol (E2) at a dose of 0.005 mg/kg/d administered s.c. for 3 days to ovariectomized rats stimulated a marked increase in the production of the 250 kDa protein. Anordiol at a low dose of 5 mg/kg/d x 3 p.o. or 0.25 mg/kg/d x 3 s.c. stimulated the production of the 250 kDa protein. Treatment with higher doses (10 mg/kg/d x 3 p.o., or 1.25 mg/kg/d x 3 s.c.) was less effective in inducing production of this protein. Also anordiol partially inhibited the stimulatory action of E2; whereas ICI 182,780, a pure antiestrogen, at a dose of 0.3 mg/kg/d x 3 s.c. completely blocked the stimulatory action of E2. The 250 kDa protein was not detected in the blood obtained from E2-treated ovariectomized rats. The anti-complement C3 and anti-alpha 2-macroglobulin antibodies did not react with the ULF 250 kDa protein. The present results show that the production of the ULF 250 kDa protein is regulated by estradiol and is not a component of blood plasma. It is proposed that the estrogen-responsive 250 kDa protein may be involved in maintaining the viability of the fertilized ova and in the implantation of the blastocyst.

Comparison of the effects of an aqueous extract of Physalis alkekengi fruits and/or various doses of 17-beta-estradiol on rat estrous cycle and uterine glucose 6-phosphate dehydrogenase activity

Intraperitoneal injections of an aqueous extract of winter cherry fruits (Physalis alkekengi) to adult normal cycling female rats produced 100% diestrus and diminished uterine glucose 6-P dehydrogenase activity (an estrogen-induced protein) by 52%. Daily doses of 1.88, 3.75 and 7.5 micrograms 17-beta-estradiol administered intraperitoneally to adult female rats for a period of 6-8 days prolonged proestrus or estrus and increased uterine glucose 6-P dehydrogenase activity by 11.5%, 26.9% and 82.1%, respectively. Combined intraperitoneal injections of a given dose of the aqueous extract together with the above doses of 17-beta-estradiol for 8 consecutive days shortened the time spent in diestrus proportional to the dose employed and proportionately reduced the uterine glucose 6-P dehydrogenase inhibitory power of the aqueous extract (1.88 micrograms estradiol, 33.9% inhibition; 3.75 micrograms estradiol, 27% inhibition; and 7.5 micrograms estradiol, 6.0% activation). The data obtained clearly demonstrate the presence of an estrogen antagonist in the aqueous extract of Physalis alkekengi fruits.

Regulation of liver glucose-6-P dehydrogenase levels in female rats

1. Gender differences in the dietary regulation of rat liver glucose-6-P dehydrogenase activity, synthesis and mRNA levels were examined. 2. As expected, in normal rats fed a standard chow diet, females have higher G6PD activity than males because they have more G6PD mRNA and therefore a higher rate of G6PD synthesis. 3. In contrast, the decreased dietary induction in female rats is due to a more rapid rate of G6PD degradation rather than a decrease in G6PD mRNA or synthesis.

Glucocorticoids repress ribosome biosynthesis in lymphosarcoma cells by affecting gene expression at the level of transcription, posttranscription and translation

Growth arrest of P1798 murine lymphosarcoma cells by glucocorticoids is accompanied by a remarkable decrease in transcription of rRNA and translation of mRNAs encoding basic ribosomal proteins (rps). Here we report that the expression of other genes involved in ribosome biogenesis is repressed in dexamethasone-treated P1798 cells. These include posttranscriptionally regulated decline in the abundance of the mRNA and primary transcript of nucleolin; abrupt drop in the transcription rate of U3 small nucleolar RNA; and inhibition of translation of mRNAs coding for P2 and L5, acidic and basic rps, respectively. Normal expression of these genes is resumed upon hormonal withdrawal.

Sexual differences as adaptation to the different gender roles in the frog Xenopus laevis Daudin

1. Various physiological parameters were determined in fed, adult, male and female Xenopus laevis acclimated to 20 degrees C and with a light: dark cycle of 12:12. The results were compared for sex differences. 2. There were significant differences in food intake, oxygen consumption, and motor activity with lower values for each parameter in males than in females (Table 1). 3. Further significant differences were found in the plasma concentrations of calcium, total lipids, and aldosterone (Table 3), in the somatic indices of fat body and gonads, in the glycogen and protein content of the liver (Table 4), and in the activities of glucose-6-phosphate dehydrogenase, fructose-1,6-diphosphatase, and phosphoenolpyruvate carboxykinase in the liver (Table 5). 4. It is assumed that the observed differences are essentially a result of differences in body growth and gametogenesis between the sexes. The lack of capacity of males to store glycogen and lipids in the male gonads is a further explanation for the differences.

Estradiol regulation of reactions involved in turnover of the amino acid acceptor terminus of tRNA in the rat uterus

Estradiol (E2) increases the specific amino acid acceptor activity of rat uterine tRNAs by increasing the proportion of certain tRNAs with intact and functional 3'-CCA acceptor termini. Activities of tRNA nucleotidyltransferase and 3'-exoribonuclease which synthesize and degrade this terminus, respectively, were measured and neither enzyme was modified by hormone treatment. Since cytidine triphosphate (CTP) levels are below reported Km values for nucleotidyltransferase, changes in CTP concentrations may regulate nucleotidyltransferase activity. An E2-induced 3-fold increase was seen in CTP synthetase activity (conversion of uridine triphosphate, UTP, into CTP). Uterine CTP levels in controls are minute (9 nmol/uterus, approx. 90 microM), and are increased 2.5-fold in E2(12 h)-treated rats. The rate of incorporation of [3H]UTP into the 3'-CCA terminus of tRNA was measured as coupled CTP synthetase-nucleotidyltransferase reactions and a 2.5-fold increase in incorporation occurred 8-12 h after E2 treatment. Injection of azaserine, (inhibitor of CTP synthetase) reduced E2-induced increases in CTP levels, CTP synthetase activity, and leucine acceptor activity of tRNAs. These results indicate that E2 regulates CTP levels by modulation of CTP synthetase activity, and that regulation of synthesis and/or repair of the 3'-CCA terminus of tRNA is proportional to E2-induced uterine cytosolic CTP levels.

Molecular mechanism of steroid hormone action during aging. A review

The application of immunochemistry coupled with genetic engineering techniques has helped greatly in the understanding of the molecular mechanism of steroid hormone action. Particularly, the recent observations on nuclear localization of steroid receptor proteins and the interaction of the steroid-receptor complex with the genome have provided much insight into the whole pathway of steroid hormone action. Despite the large amount of data accumulated over the years on the mechanism of steroid action in general, relatively little is known about the changes occurring in the action of steroid hormones during aging. However, there is some evidence of a decreased responsiveness of target tissues to steroid hormones during senescence. In the light of recent progress in steroid research, an attempt has been made in this article to discuss the alterations that occur at different steps of steroid action as a function of age.

Estradiol regulation of the synthesis of uterine proteins with clusters of proline- and glycine-rich peptide sequences

Estradiol (E2) regulates the synthesis of uterine proteins at both the transcriptional and translational levels. E2 induces an increase in the specific amino acid acceptor activity of uterine tRNA, with the largest increases seen for proline, glycine and methionine. The synthesis of three uterine proteins that are rich in proline and glycine, estrogen receptor, progesterone receptor and glucose-6-phosphate dehydrogenase, is induced by E2. E2-induced increases in these proteins were preceded by an correlated with stimulation of tRNA acceptor activity for proline and glycine and these responses were specifically and simultaneously inhibited by prior azaserine treatment, which inhibits the E2-induced repair and synthesis of the 3'-CCA acceptor terminus of tRNAs. The high frequency and clustering of proline and glycine residues in estrogen receptor, progesterone receptor and glucose-6-phosphate dehydrogenase suggests that the translating ribosomes may slow down during synthesis of these proteins due to limiting levels of these tRNAs in E2-deprived uteri.

Differential effects of 1,25-dihydroxyvitamin D3 upon intestinal vitamin D3-dependent calbindin (a 28,000-dalton calcium binding protein) and its mRNA in D-replete and D-deficient chickens

The effect of vitamin D3 status upon the responsiveness of chick intestinal epithelium to exogenous 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] was studied. Intestinal calbindin [A recent consensus decision was made to redesignate the vitamin D-dependent calcium binding protein as "calbindin-D28K" (R.H. Wasserman (1985) in Vitamin D: Chemical, Biochemical, and Clinical Update (Norman, A.W., Schaefer, K., Grigoleit, H.-G., and Herrath, D.V., Eds.), pp. 321-322, de Gruyter, Berlin/New York).] protein and intestinal calbindin mRNA were quantitated in birds which had been raised on a vitamin D3-deplete (-D) or on a vitamin D3-replete (+D) diet. 1,25(OH)2D3 stimulated intestinal calbindin mRNA levels in -D chickens in a proportional dose-dependent manner, when measured at both 12 and 48 h after administration of the hormone. A first increase was observed with 1,25(OH)2D3 concentrations between 0.065 and 0.65 nmol. The maximal stimulation achieved by 1,25(OH)2D3 (6.5-18 nmol) in -D tissue was approximately 10-fold over the calbindin mRNA levels present in vehicle-treated birds. The increase of calbindin mRNA in -D birds was associated with a similar dose-dependent increase in calbindin protein in 1,25(OH)2D3-treated -D birds after 12 or 48 h. In +D intestine, while exogenous 1,25(OH)2D3 also increased calbindin mRNA levels in a dose-dependent fashion, the maximal stimulation observed after 5 h (1.2- to 2-fold) was clearly less than that observed in -D intestine. In contrast to -D birds, intestinal calbindin levels in +D birds were decreased by administration of exogenous 1,25(OH)2D3. Administration of 32.5 to 65 nmol 1,25(OH)2D3 resulted in an approximately 1.8-fold repression compared to vehicle-treated birds. This differential responsiveness between +D and -D intestines with respect to 1,25(OH)2D3 was not explained either by differences in the uptake in the chromatin fractions of these tissues or by metabolism of radiolabeled 1,25(OH)2D3. Dietary withdrawal of vitamin D3 led to a gradual decline in ambient intestinal calbindin levels, while intestinal sensitivity to 1,25(OH)2D3 was restored. These findings suggest that vitamin D3 status regulates intestinal responsiveness to the seco-steroid 1,25(OH)2D3.

Glucocorticoids selectively inhibit translation of ribosomal protein mRNAs in P1798 lymphosarcoma cells

When P1798 murine lymphosarcoma cells are exposed to 10(-7) M dexamethasone, there is a dramatic inhibition of rRNA synthesis, which is completely reversible when the hormone is withdrawn. In the present experiments we examined whether dexamethasone treatment causes any alteration in the accumulation or utilization of mRNAs that encode ribosomal proteins (rp mRNAs). No effect on the accumulation of six different rp mRNAs was detected. However, the translation of five of six rp mRNAs was selectively inhibited in the presence of the hormone, as judged by a substantial decrease in ribosomal loading. Normal translation of rp mRNA was resumed within a few hours after hormone withdrawal. In untreated or fully recovered cells, the distribution of rp mRNAs between polyribosomes and free ribonucleoprotein is distinctly bimodal, suggesting that rp mRNAs are subject to a particular form of translational control in which they are either translationally inactive or fully loaded with ribosomes. A possible relationship between this mode of translational control and the selective suppression of rp mRNA translation by glucocorticoids is discussed.

Detection of estrogen receptor mRNA in human uterus

We transcribed a cDNA clone of the human estrogen receptor (ER) with T7 RNA polymerase. The 32P-cRNA transcript complementary to ER mRNA was hybridized to poly(A)+ RNA from human uterus and revealed a single band of approximately 4.2 kilobases. No hybridization was seen with the cRNA probe of the opposite orientation. Hybridization of total RNA from calf and rat uterus yielded a single band at approximately 3.8 kilobases for both species. Total RNA from rat spleen did not hybridize. A 35S-labeled cRNA probe was prepared for in situ hybridization of ER mRNA in human uterus and spleen. Autoradiographic signal was present over endometrial epithelium, stromal cells of the lamina propria, and smooth muscle cells of the myometrium but was absent from sections of spleen. The ER mRNA hybridization label was located over cytoplasm and nuclei of uterine target cells.

Glucocorticoids selectively inhibit translation of ribosomal protein mRNAs in P1798 lymphosarcoma cells

When P1798 murine lymphosarcoma cells are exposed to 10(-7) M dexamethasone, there is a dramatic inhibition of rRNA synthesis, which is completely reversible when the hormone is withdrawn. In the present experiments we examined whether dexamethasone treatment causes any alteration in the accumulation or utilization of mRNAs that encode ribosomal proteins (rp mRNAs). No effect on the accumulation of six different rp mRNAs was detected. However, the translation of five of six rp mRNAs was selectively inhibited in the presence of the hormone, as judged by a substantial decrease in ribosomal loading. Normal translation of rp mRNA was resumed within a few hours after hormone withdrawal. In untreated or fully recovered cells, the distribution of rp mRNAs between polyribosomes and free ribonucleoprotein is distinctly bimodal, suggesting that rp mRNAs are subject to a particular form of translational control in which they are either translationally inactive or fully loaded with ribosomes. A possible relationship between this mode of translational control and the selective suppression of rp mRNA translation by glucocorticoids is discussed.

A distinct glucocorticoid hormone response regulates phosphoprotein maturation in rat hepatoma cells

Glucocorticoid hormone-dependent maturation of the mouse mammary tumor virus (MMTV) phosphorylated polyprotein (Pr74) allows experimental access to certain posttranslational regulatory circuits under steroid control in M1.54 cells, an MMTV-infected rat hepatoma cell line. Pulse-chase experiments revealed that [35S]methionine-labeled Pr74 synthesized in uninduced cells could be converted posttranslationally into p24, a stable phosphorylated maturation product, only after 4 h of exposure to 1 microM dexamethasone, a synthetic glucocorticoid. This regulated processing could be prevented by prior exposure, during the chase period, to inhibitors of RNA (actinomycin D) or protein (cycloheximide or puromycin) synthesis. Moreover, half-maximal production of p24 occurred at 10 nM dexamethasone, a concentration that approximated half-maximal receptor binding and stimulation of MMTV transcript synthesis. Kinetic, hormonal, and genetic evidence suggest that p24 expression did not require or result from the overall glucocorticoid-dependent increase in polyprotein concentration. First, 20 h after dexamethasone withdrawal, Pr74 maturation was completely deinduced, whereas the absolute level of this MMTV precursor remained 10-fold over its basal level. Second, progesterone, which competes with dexamethasone for receptor binding, facilitated the regulated production of p24 but prevented the steroid-mediated accumulation of functional MMTV mRNA. Lastly, certain glucocorticoid-responsive variants, derived from M1.54 cells by resistance to complement cytolysis, expressed p24 in the presence or absence of glucocorticoid-induced levels of Pr74. Taken together, our results suggest that the glucocorticoid-regulated maturation of MMTV phosphopolyproteins resulted from an independent hormone response that required normal receptor function and de novo RNA and protein synthesis.

Sex-linked changes in immunoreactive glucose-6-phosphate dehydrogenase in rat liver

The level of hepatic immunoreactive glucose-6-phosphate dehydrogenase protein was found to correlate well with the enzyme activity in adult rats fed the stock laboratory diet in a variety of hormonal conditions. The amount of immunoreactive protein and enzyme activity was 2-fold greater in sexually mature female rats compared with aged matched male animals. However, this difference was absent in diabetic animals, and furthermore although triiodothyronine administration to the diabetic male rat could restore the level of enzyme activity to that of the normoglycaemic animal, it was much less effective in the female animal. In contrast, administration of insulin to the normoglycaemic animal increased the level of glucose-6-phosphate dehydrogenase in the female, but was without effect in the male. These results are discussed in relation to the possible role of thyroid status and steroid sex hormones in the regulation of hepatic glucose-6-phosphate dehydrogenase.

Isolation of a precursor and a nascent chain form of glucose-6-phosphate dehydrogenase from rat uterus and regulation of precursor processing by estradiol

SDS-polyacrylamide gel electrophoresis of anti-glucose-6-phosphate dehydrogenase immunoprecipitates from radiolabeled uterine tissue extracts previously revealed three proteins: A, B and C, which were tentatively identified as a 60-64 kDa precursor form, a 57 kDa predominant form, and a 40-42 kDa nascent peptide form of the enzyme, respectively. A peptide-mapping technique was used to examine structural homologies among A, B and C. Following the labeling of uterine proteins with [35S]methionine, labeled proteins A, B and C were isolated by immunoprecipitation and electrophoresis. Each protein was individually co-digested with authentic, [3H]methionine-labeled glucose-6-phosphate dehydrogenase using papain, the resulting peptides were resolved by isoelectric focusing and the peptides from the two sources on each gel were compared using double-label counting methods. Proteins A, B and C had at least eight peptides in common, both proteins A and C had two additional peptides in common that were not present in protein B, and B protein had two peptides that were either absent or present in reduced amounts in digests of proteins A and C. The extensive structural homology and immunoreactivity of these proteins indicated that proteins A, B and C were all related to glucose-6-phosphate dehydrogenase. The presence of two extra peptides in proteins A and C suggested that these peptides may be derived from a common NH2-terminal leader sequence which was present in both the precursor and nascent peptide chains. The presence of two peptides that were present in protein B and absent from proteins A and C is easiest to explain if they are derived from the two ends of the molecule, with the corresponding peptides in proteins A and C containing additional peptide sequences that are 'normally' removed by endogenous proteolytic processing enzymes. Based on the relative time-course of synthesis of the three glucose-6-phosphate dehydrogenase-related proteins in control and estrogen-treated uteri, it appears that estradiol promotes an increase in the relative rate of transfer of label from protein A into B by stimulating the rate of processing of the precursor to the predominant form of the enzyme and enhances the rate of translational conversion of protein C into higher molecular weight forms.

A distinct glucocorticoid hormone response regulates phosphoprotein maturation in rat hepatoma cells

Glucocorticoid hormone-dependent maturation of the mouse mammary tumor virus (MMTV) phosphorylated polyprotein (Pr74) allows experimental access to certain posttranslational regulatory circuits under steroid control in M1.54 cells, an MMTV-infected rat hepatoma cell line. Pulse-chase experiments revealed that [35S]methionine-labeled Pr74 synthesized in uninduced cells could be converted posttranslationally into p24, a stable phosphorylated maturation product, only after 4 h of exposure to 1 microM dexamethasone, a synthetic glucocorticoid. This regulated processing could be prevented by prior exposure, during the chase period, to inhibitors of RNA (actinomycin D) or protein (cycloheximide or puromycin) synthesis. Moreover, half-maximal production of p24 occurred at 10 nM dexamethasone, a concentration that approximated half-maximal receptor binding and stimulation of MMTV transcript synthesis. Kinetic, hormonal, and genetic evidence suggest that p24 expression did not require or result from the overall glucocorticoid-dependent increase in polyprotein concentration. First, 20 h after dexamethasone withdrawal, Pr74 maturation was completely deinduced, whereas the absolute level of this MMTV precursor remained 10-fold over its basal level. Second, progesterone, which competes with dexamethasone for receptor binding, facilitated the regulated production of p24 but prevented the steroid-mediated accumulation of functional MMTV mRNA. Lastly, certain glucocorticoid-responsive variants, derived from M1.54 cells by resistance to complement cytolysis, expressed p24 in the presence or absence of glucocorticoid-induced levels of Pr74. Taken together, our results suggest that the glucocorticoid-regulated maturation of MMTV phosphopolyproteins resulted from an independent hormone response that required normal receptor function and de novo RNA and protein synthesis.

Multiple-level caerulein control of the gene expression of secretory proteins in the rat pancreas

Continuous intravenous infusion of caerulein (0.25 micrograms X kg-1 X h-1) has recently been reported [Schick, J., Kern, H. & Scheele, G. (1984) J. Cell Biol. 99, 1569-1574] to enhance significantly the synthesis of both trypsinogen and chymotrypsinogen and to decrease that of amylase in the rat pancreas. With a view to achieving a better understanding of the mechanisms underlying caerulein modulation of pancreatic gene expression, the relative levels of active mRNA corresponding to these proteins were determined in caerulein-stimulated animals and compared to those of controls infused with a 0.9% NaCl solution. For this purpose, the translation products synthesized in vitro in a rabbit reticulocyte lysate translation system were measured. Prolonged caerulein infusion had less pronounced effects on mRNA levels as determined by the relative synthesis of translation products than on individual secretory proteins. No changes in mRNA levels were observed during 6 h of hormonal stimulation, whereas a 7-fold increase in the ratio of trypsinogen to amylase synthesis was obtained previously. After 24 h of caerulein infusion, only a slight change in active mRNA coding for amylase (1.7-fold) and serine protease zymogens (1.4-fold) occurred as compared to 14-fold and 2-fold variations in the synthesis rates of the corresponding proteins. These findings indicate that caerulein exerts a predominantly translational control on the biosynthesis of pancreatic amylase, trypsinogen and chymotrypsinogen even after 24 h of hormonal stimulation. However, additional control at a transcriptional or post-transcriptional level (i.e. via messenger RNA stability) may well take place.

Molecular aspects of erythroenzymopathies associated with hereditary hemolytic anemia

Since the discovery of glucose 6-phosphate dehydrogenase (G6PD) and of pyruvate kinase deficiencies, erythroenzymopathies associated with hereditary hemolytic anemia have been extensively investigated. Kinetic and electrophoretic studies have shown that most, if not all, erythroenzymopathies are caused by the production of a mutant enzyme. Except for a few enzymes that are abundant in blood and tissues, it is difficult to obtain enough sample to study the functional and structural abnormalities of mutant enzymes associated with genetic disorders in man. The primary structures of only two normal red cell enzymes which can cause hereditary hemolytic anemia, phosphoglycerate kinase (PGK) and adenylate kinase, have been determined. Single amino acid substitutions of PGK variants have been found, and the identification of the exact molecular abnormalities of such variants has helped us to understand the accompanying functional abnormality. Gene cloning makes possible the identification of the DNA sequence that codes for enzyme proteins. Recently, human complementary DNA (cDNA) for aldolase, PGK, G6PD, and adenosine deaminase (ADA) have been isolated, and the nucleotide sequences for PGK and ADA determined. In the near future, human cDNA sequencing should permit identification of the gene alteration that gives rise to the mutant enzymes.

Inhibition of the aminoacylation of selected tRNA molecules by an estrogen-regulated factor on uterine ribosomes. Regulation of aminoacylation of tRNA by estrogens

Administration of estradiol to ovariectomized mature rats for 1 h induces a transient increase in the peptide elongation rate on uterine ribosomes. An inhibitor of the peptide elongation rate, which appears to be regulated by estrogen treatment in vivo, can be extracted from ribosomes of estrogen-deprived rats. The extracted inhibitor or a native inhibitor-ribosome complex affects the rate of the peptide elongation reaction in a uterine cell-free protein synthesis system by inhibiting the ability of selected tRNAs in the assay to be charged with amino acids by their respective aminoacyl-tRNA synthetases. The degree of inhibition of charging of the affected tRNAs ranges from 22% to 78%, the order of inhibition being Pro greater than Val greater than Arg greater than Try greater than Leu greater than Glu greater than Ile greater than Gly greater than His greater than Ser greater than Lys. Inhibition results from a specific dose-dependent, and presumably reversible, effect of the inhibitor on tRNA, but not on the aminoacyl-tRNA synthetase. The effect does not result from removal of A-C-C terminal nucleotides from the 3' end of tRNA, but does inhibit the ability of selected tRNAs to bind to the aminoacyl-tRNA synthetases. We propose that regulation of the peptide elongation rate on uterine ribosomes by estradiol occurs through the estradiol-induced inactivation of a ribosome-associated inhibitor, which causes a reversible alteration to selected tRNAs. The modified tRNAs are unable to bind to their respective aminoacyl-tRNA synthetase to become charged with an amino acid thus causing the availability of selected aminoacyl-tRNAs to become rate-limiting in the sequential elongation of peptides.