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PubMed1982

Further studies on the mechanism of phosphorylase activation in rabbit liver in response to splanchnic nerve stimulation.

1. The mechanism of activation of liver phosphorylase after splanchnic nerve stimulation has been investigated in rabbits and compared with the effects of intraportal injections of noradrenaline.2. The increase in the activity of liver phosphorylase-a, the active form of this key glycogenolytic enzyme, in response to injections of noradrenaline was blocked by beta-adrenergic antagonists, but not by alpha-adrenergic antagonists, suggesting that the effect of noradrenaline is mediated mainly through beta-adrenoceptors in vivo. In contrast, the increase in phosphorylase activity in response to stimulation of the peripheral end of the splanchnic nerve was resistant to both alpha- and beta-adrenoceptor blockade.3. When diltiazem and verapamil, selective Ca(2+) antagonists that restrict calcium influx across the cell membrane, were infused intraportally, the phosphorylase response to splanchnic nerve stimulation was virtually abolished, while the response to noradrenaline was unaltered.4. Infusion of the prostaglandin-synthesis inhibitor indomethacin at a dose of 3.4 mug/min was found to block the activation of liver phosphorylase in response to stimulation of the splanchnic innervation.5. These results suggest that the mechanism whereby stimulation of the sympathetic innervation to the liver leads to activation of phosphorylase is not mediated by either alpha- or beta-adrenoceptors, but appears to depend upon prostaglandin formation and influx of Ca(2+) ions into the hepatocytes.

Adrenergic alpha-Antagonists↗
PubMed1989

Intensity and duration of exercise effects on skeletal muscle cAMP, phosphorylase, and glycogen.

To gain further insights into the mechanisms regulating skeletal muscle glycogenolysis during exercise, glycogen, phosphorylase, and adenosine 3',5'-cyclic monophosphate (cAMP) were determined in fast-twitch white (FTW) and fast-twitch red (FTR) muscle from groups of rats that ran for 0, 5, 10, 15, or 30 min at either 15 or 30 m/min. Glycogen degradation demonstrated an intensity and duration response in both fiber types. cAMP increased in both fiber types by 5 min and remained elevated at all times measured. FTW muscle cAMP levels were independent of both intensity and duration of exercise. FTR muscle cAMP levels were higher from 10 to 30 min at the 30-m/min intensity compared with the 15-m/min intensity. The ratio of the activity of phosphorylase in the presence of 2 mM AMP X 100 (phosphorylase a%) remained elevated at 20-22% independent of intensity and duration in FTW muscle; however, phosphorylase a% demonstrated an intensity and duration effect in FTR muscle. Glycogenolytic rates decreased with time, even though both cAMP and phosphorylase a% remained elevated in both fiber types. These data suggest that cAMP and phosphorylase a activation can be maintained during exercise in skeletal muscle but indicate a dissociation of these factors from glycogenolysis.

Animals↗
PubMed1976

Evidence for the coordinate control of activity of liver glycogen synthase and phosphorylase by a single protein phosphatase.

Homogeneous rabbit liver phosphorylase phosphatase (Brandt, H., Capulong, Z. L., and Lee, E. Y. C. (1975) J. Biol. Chem. 250, 8038-8044) also dephosphorylates glycogen synthase b. During purification, phosphorylase phosphatase and glycogen synthase phosphatase co-purified with a constant ratio of activities. The two activities co-migrated on disc gel electrophoresis. Both substrates competed with each other for the phosphatase, and both phosphatase activities were inhibited by lysine ethyl ester. It is concluded that liver phosphorylase phosphatase and glycogen synthase phosphatase have a common identity and that coordinate regulation of the phosphatase-catalyzed activation of glycogen synthase and inactivation of phosphorylase occurs in vivo. This provides a parallel and opposing mechanism to that mediated by adenosine 3':5'-monophosphate-dependent protein kinase, which coordinately inactivates glycogen synthase and, via phosphorylase kinase, activates phosphorylase. Maximal glycogen synthase phosphatase activity was observed near neutrality. Mg2+ and glucose-6-P activated the glycogen synthase phosphatase reaction and this activation was pH-dependent. The Km for glycogen synthase b was 0.12 muM.

Animals↗
PubMed1983

Phosphorylase ratio and susceptibility to malignant hyperthermia.

The ratio of muscle phosphorylase a to total phosphorylase, expressed as a percent, was determined in vastus lateralis muscle of 26 patients to examine the efficacy of this parameter as a method for screening for susceptibility to malignant hyperthermia (MH). As standard screening, all patients also had muscle contracture responses determined to 2% halothane and 0.25-32 mM caffeine at 37 degrees C. Each drug was given separately and not combined. Nine patients were susceptible to MH, based upon caffeine threshold of 2 mM or less (seven patients) or a rapidly developing contracture tension to halothane of more than 400 mg (seven patients, including five with positive caffeine responses). Mean phosphorylase ratio in these nine patients was 14.5 +/- 2.0% (mean, SEM). In the 17 nonsusceptible patients mean phosphorylase ratio (12.4 +/- 1.9%) was not significantly different. The range of phosphorylase ratios in susceptible patients was 6.5-26% while 13 nonsusceptible patients had ratios greater than 6% and up to 29%. The unacceptably high number of false-positive responses in nonsusceptible patients precludes the use of phosphorylase ratio as a definitive diagnostic test.

Adolescent↗
PubMed1984

Structural changes in phosphorylase b as revealed by proteolysis with subtilisin BPN'.

The proteolysis of rabbit skeletal muscle phosphorylase b was studied with Sepharose 4B bound subtilisin BPN' in the absence and presence of various ligands. The proteolysis was carried out at pH 7.0 and pH 8.5 and was followed by measuring phosphorylase b activity and by SDS gel electrophoresis. The effect of ligands proved to be qualitatively the same at both pH values. It was found that AMP and alpha-D-glucose-1-phosphate accelerated the inactivation of phosphorylase b by subtilisin, two main proteolytic products (Mr 70 000 and 30 000) were formed in the presence of these ligands. IMP and glycogen protected phosphorylase b against proteolytic attack. Subtilisin treatment in the presence of D-glucose, caffeine and D-glucose-6-phosphate produced a reproducible increase (about 20%) of phosphorylase b activity. This "activation" resulted in an increased Vmax of phosphorylase b though did not alter the subunit size, the aggregation state and the ligand binding capacity of the enzyme.

Animals↗
PubMed1983

Effects of the calmodulin antagonist, fluphenazine, on phosphorylation of myosin and phosphorylase in intact smooth muscle.

The activities of phosphorylase kinase and myosin light-chain kinase are regulated by Ca2+ binding to calmodulin. However, differences in the activation properties of the purified enzymes are apparent, since calmodulin binds to phosphorylase kinase in the absence of Ca2+ whereas prior formation of a Ca2+ . calmodulin complex is necessary for calmodulin to bind to and activate myosin light chain kinase. Since the phenothiazines have been implicated as anticalmodulin drugs and inhibit contractile activity in smooth muscle, we examined the effects of the phenothiazine, fluphenazine, on isometric tension development and phosphorylation of phosphorylase and the phosphorylatable light chain (P-light chain) of myosin in intact bovine tracheal smooth muscle. Preincubation with 50 microM fluphenazine for 5 min inhibited the maximal rate and extent of isometric tension development and P-light chain phosphorylation in the presence of 60 mM KCl. Application of fluphenazine after tension and the phosphate content of the P-light chain had reached steady-state levels in response to 60 mM KCl produced little relaxation or dephosphorylation of the P-light chain. KCl-mediated phosphorylase a formation was not inhibited by preincubation with fluphenazine for 5 min. However, long periods of preincubation (30-60 min) produced significant inhibition of phosphorylase a formation and proportionally greater inhibition of tension and P-light chain phosphorylation. Since phosphorylase a formation was not inhibited during short-term preincubation with fluphenazine, KCl-dependent increases in the concentration of free intracellular Ca2+ may not have been affected. Moreover, since both isometric tension development and P-light chain phosphorylation were attenuated in a parallel manner, inhibition of contractile activity in intact smooth muscle by anticalmodulin agents may be directly related to inhibition of P-light chain phosphorylation.

Animals↗
PubMed1999

Hormonal activation of phosphorylase in cockroach fat body trophocytes: A correlation with trans-membrane calcium flux.

This study is an investigation of the temporal relationship between transmembrane Ca(2+) fluxes, and glycogen phosphorylase activation in dispersed trophocytes from the fat body of the cockroach, Periplaneta americana. Phosphorylase is maximally activated within 5 min after treating the trophocytes with either of the hypertrehalosemic hormones, Pea-HTH-I and Pea-HTH-II. Activation caused by Pea-HTH-II is sustained for a longer period than that produced by Pea-HTH-I. Chelation of extracellular Ca(2+) with EGTA blocks the activation of phosphorylase by HTH. Similarly, chelation of intracellular Ca(2+) with Quin 2 greatly diminishes the phosphorylase activating effect of both HTHs. The data support the view that an increase in the intracellular Ca(2+ )concentration is required for the activation of phosphorylase and that extracellular Ca(2+) is an essential, although not necessarily sole, source of Ca(2+) for this purpose. Using (45)Ca(2+) to trace the movement of Ca(2+) following a challenge with either Pea-HTH-I or -II, it was shown that (45)Ca(2+)influx nearly doubled during the first 30 s. At this time, the trophocytes begin to expel Ca(2+) at a rate higher than that of untreated cells and this state persists for approximately 4 min. The Ca(2+) fluxes are consistent with its postulated role in the activation of phosphorylase. Arch.

Aminoquinolines↗
PubMed1992

A comparison of glycogen phosphorylase a and cytochrome oxidase histochemical staining in rat brain.

The utility of metabolic markers that index functional neuronal circuits is widely appreciated. The present study asks whether patterns of the metabolic enzyme, active glycogen phosphorylase, parallel those of the neuronal marker, cytochrome oxidase. Fresh frozen rat brain sections (30 microns) were processed for either active glycogen phosphorylase or cytochrome oxidase at each of ten levels of the neuraxis. Although these metabolic markers predominate in different cellular compartments--glycogen phosphorylase in the astrocytic compartment and cytochrome oxidase in the neuronal compartment--the patterns of high, moderate, and low levels of activity for both enzymes were generally parallel. These similarities extended to detailed patterns of heterogeneous staining within structures, in particular, to laminated and modular distribution within cerebral and cerebellar cortical structures. The modular distribution was evident in barrel structures in the cerebral cortex and in parasagittal compartments in the vermis of the cerebellum. Conspicuous differences between the two patterns occurred in white matter, in subcortical grey matter regions such as the nucleus accumbens, diagonal band, amygdala, and globus pallidus, and in the superior olivary nuclei of the brainstem as well as in nonneural structures such as the choroid plexus and ependyma. Discrete patchiness was characteristic of active glycogen phosphorylase distribution in the limbic neuropil of the dentate gyrus and entorhinal cortex. The strong parallels between active glycogen phosphorylase and cytochrome oxidase distribution support the view that glycogen phosphorylase, despite its glial localization, can reflect neuronal metabolic demands.

Animals↗
PubMed1995

N-acetyl-beta-D-glucopyranosylamine: a potent T-state inhibitor of glycogen phosphorylase. A comparison with alpha-D-glucose.

Structure-based drug design has led to the discovery of a number of glucose analogue inhibitors of glycogen phosphorylase that have an increased affinity compared to alpha-D-glucose (Ki = 1.7 mM). The best inhibitor in the class of N-acyl derivatives of beta-D-glucopyranosylamine, N-acetyl-beta-D-glucopyranosylamine (1-GlcNAc), has been characterized by kinetic, ultracentrifugation, and crystallographic studies. 1-GlcNAc acts as a competitive inhibitor for both the b (Ki = 32 microM) and the a (Ki = 35 microM) forms of the enzyme with respect to glucose 1-phosphate and in synergism with caffeine, mimicking the binding of glucose. Sedimentation velocity experiments demonstrated that 1-GlcNAc was able to induce dissociation of tetrameric phosphorylase a and stabilization of the dimeric T-state conformation. Co-crystals of the phosphorylase b-1-GlcNAc-IMP complex were grown in space group P4(3)2(1)2, with native-like unit cell dimensions, and the complex structure has been refined to give a crystallographic R factor of 18.1%, for data between 8 and 2.3 A resolution. 1-GlcNAc binds tightly at the catalytic site of T-state phosphorylase b at approximately the same position as that of alpha-D-glucose. The ligand can be accommodated in the catalytic site with very little change in the protein structure and stabilizes the T-state conformation of the 280s loop by making several favorable contacts to Asn 284 of this loop. Structural comparisons show that the T-state phosphorylase b-1-GlcNAc-IMP complex structure is overall similar to the T-state phosphorylase b-alpha-D-glucose complex structure. The structure of the 1-GlcNAc complex provides a rational for the biochemical properties of the inhibitor.

Animals↗
PubMed1987

Modeling the biochemical differences between rabbit muscle and human liver phosphorylase.

Glycogen phosphorylases catalyze the regulated breakdown of glycogen to glucose-1-phosphate. In mammals, glycogen phosphorylase occurs in three different isozymes called liver, muscle, and brain after the tissues in which they are preferentially expressed. The muscle isozyme binds and is activated cooperatively by AMP. In contrast, the liver enzyme binds AMP noncooperatively and is poorly activated. The amino acid sequence of human liver phosphorylase is 80% identical with rabbit muscle phosphorylase, and those residues which contact AMP are conserved. Using computer graphics software, we replaced side chains of the known rabbit muscle structure with those of human liver phosphorylase and interpreted the effects of these changes in order to account for the biochemical differences between them. We have identified two substitutions in liver phosphorylase potentially important in altering the cooperative binding and activation of this isozyme by AMP.

Adenosine Monophosphate↗
PubMed1995

Determination of plasma purine nucleoside phosphorylase activity by high-performance liquid chromatography.

A high-performance liquid chromatographic method was developed for the determination of plasma purine nucleoside phosphorylase activity. In this method, the reaction mixture consisted of 15 microliters of plasma and 285 microliters of 50 mM phosphate buffer (pH 7.4) containing 3.8 mM inosine and 0.15 mM 2-(3-cyano-4-isobutoxyphenyl)-4-methyl-5-thiazolecarboxylic acid (strong xanthine oxidase inhibitor). After the reaction, the hypoxanthine produced was monitored to express plasma purine nucleoside phosphorylase activity. By this method, the activity of purine nucleoside phosphorylase was easily determined even with a small-volume plasma sample and despite its low activity in plasma. In addition, plasma purine nucleoside phosphorylase activity can be accurately determined even if the plasma is turbid. As a result, we were able to measure plasma purine nucleoside phosphorylase activity in patients with gout or asthma and healthy subjects, whereby it was demonstrated that plasma purine nucleoside phosphorylase activity was higher in patients with asthma than in either healthy subjects or patients with gout.

Adult↗
PubMed1996

Purification and characterization of recombinant human 5'-methylthioadenosine phosphorylase: definite identification of coding cDNA.

5'-Methylthioadenosine phosphorylase gene maps on the 9p21 chromosome, strictly linked to the important tumor suppressor gene p16INK4A. Chromosomal deletions encompassing both the phosphorylase and p16INK4A genes cause the complete absence of the enzymatic activity in a large number of tumors, thus resulting in well-defined metabolic differences between malignant and normal cells. Recently, the cloning of the phosphorylase gene has been reported on the basis of indirect evidence. In order to demonstrate definitely the identification of 5'-methylthioadenosine phosphorylase gene, we have cloned the putative enzyme coding sequence in a prokaryotic expression vector and expressed the protein in bacteria. The recombinant phosphorylase has been purified to homogeneity and its physicochemical, immunological and kinetic features have been characterized. The results obtained allowed the conclusive demonstration of 5'-methylthioadenosine phosphorylase gene cloning and the use of recombinant protein for further characterization.

Chromatography, Gel↗
PubMed1995

The binding of 2-deoxy-D-glucose 6-phosphate to glycogen phosphorylase b: kinetic and crystallographic studies.

Kinetic and crystallographic studies have characterized the effect of 2-deoxy-glucose 6-phosphate on the catalytic and structural properties of glycogen phosphorylase b. Previous work on the binding of glucose 6-phosphate, a potent physiological inhibitor of the enzyme, to T state phosphorylase b in the crystal showed that the inhibitor binds at the allosteric site and induces substantial conformational changes that affect the subunit-subunit interface. The hydrogen-bond from the O-2 hydroxyl of glucose 6-phosphate to the main-chain oxygen of Val40' represents the only hydrogen bond from the sugar to the other subunit, and this interaction appears important for promoting a more "tensed" structure than native T state phosphorylase b. 2-Deoxy-glucose 6-phosphate acts competitively with both the activator AMP and the substrate glucose 1-phosphate, with Ki values of 0.53 mM and 1.23 mM, respectively. The binding of 2-deoxy-glucose 6-phosphate to T state glycogen phosphorylase b in the crystal, has been investigated and the complex phosphorylase b: 2-deoxy-glucose 6-phosphate has been refined to give a crystallographic R factor of 17.3%, for data between 8 A and 2.3 A. 2-Deoxy-glucose 6-phosphate binds at the allosteric site as the a anomer and adopts a different conformation compared to glucose 6-phosphate. The two conformations differ by 160 degrees in the torsion angle about the C-5-C-6 bond. The contacts from the phosphate group are essentially identical to those made by the phosphate of glucose 6-phosphate but the 2-deoxy glucosyl moiety binds in a quite different orientation compared to the glucosyl of glucose 6-phosphate. 2-Deoxy-glucose 6-phosphate can be accommodated in the allosteric site with very little change in the protein, while structural comparisons show that the phosphorylase b: 2-deoxy-glucose 6-phosphate complex structure is overall more similar to a glucose-like complex than to the Glc-6-P complex structure.

Allosteric Site↗
PubMed1980

X-linked dominant inheritance of partial phosphorylase kinase deficiency in mice.

A new mouse strain, the V strain, with a partial deficiency of phosphorylase kinase has been established. The deficiency is caused by an X-linked dominant gene (PhKc). Muscle extracts of homozygous and heterozygous females and hemizygous males have about 25% of the activity found in extracts of normal (C3H/HeHan) mice. This dominant phosphorylase kinase deficiency of the new V strain is different from that of the I-strain mice with the X-linked recessive deficiency of skeletal muscle phosphorylase kinase. The muscle extracts of V-strain and normal mice contain the same phosphorylase phosphatase activity of about 1 U/mg. Heart and liver extracts from V mice contained about 50% and 66%, respectively, of the phosphorylase kinase activity compared to that found in the same organs from the normal mice. The glycogen content of the skeletal muscle of the V strain was normal, i.e., 0.9 mg/g. Phosphorylase kinase was purified from the skeletal muscle of the V strain by (a) hydrophobic chromatography on methylamine Sepharose, (b) ammonium sulfate precipitation, and (c) gel filtration of Sepharose 4B. The enzyme has a similar structure to the normal murine and rabbit skeletal muscle enzyme, except that the proportion of the subunits differs. The molar ratio of the subunits of the V strain mice is (alpha + alpha'):beta:gamma=0.54:1:1.169, in comparison with that of the rabbit (alpha + alpha'):beta:gamma=1.1:1.0:1.0 and that of normal murine enzyme 0.9:1.0:0.7.

Animals↗
PubMed1979

Characterization of the subunits of purine nucleoside phosphorylase from cultured normal human fibroblasts.

In previous communications we have demonstrated that the subunits of normal human erythrocyte purine nucleoside phosphorylase can be resolved into four major (1-4) and two minor (1p and 2p) components with the same molecular weight but different apparent isoelectric points (and net ionic charge). The existence of subunits with different charge results in a complex isoelectric focusing pattern of the native erythrocytic enzyme. In contrast, the isoelectric focusing pattern of the native enzyme obtained from cultured human fibroblasts is simpler. The multiple native isoenzymes obtained from human erythrocytes and human brain have isoelectric points ranging from 5.0 to 6.4 and from 5.2 to 5.8 respectively, whereas cultured human fibroblasts have two major native isoenzymes with apparent isoelectric points of 5.1 and 5.6. Purine nucleoside phosphorylase has been purified at least a hundredfold from 35S-labeled cultured human fibroblasts. A two-dimensional electrophoretic analysis of the denatured purified normal fibroblast enzyme revealed that it consists mainly of subunit 1 (90%) with small amounts of subunits 2 (10%) and 3 (1%). This accounts for the observed differences between the native isoelectric focusing and the electrophoretic patterns of the erythrocyte and fibroblast enzymes. The purine nucleoside phosphorylase subunit 1 is detectable in the autoradiogram from a two-dimensional electrophoretic analysis of a crude, unpurified extract of 35S-labeled cultured normal human fibroblasts. The fibroblast phosphorylase coincides with the erythrocytic subunit 1 of the same enzyme, and the cultured fibroblasts of a purine nucleoside phosphorylase deficient patient (patient I) lack this protein component, genetically confirming the identity of the purine nucleoside phosphorylase subunit in cultured fibroblasts.

Apoenzymes↗
PubMed1993

Preparation and functional characterization of a catalytically active fragment of phosphorylase kinase.

Limited proteolysis of rabbit muscle phosphorylase kinase catalyzed by chymotrypsin generates a 33 kD product whose kinase activity is independent of both calcium and pH over the range of 6.8 to 8.3 (Malencik, D.A. & Fischer, E.H. Calcium and Cell Function III: 161-188, 1982). This active preparation consists of three related species containing residues 1-290, 1-296, and 1-298 of the 44.7 kD gamma-subunit of phosphorylase kinase (Harris, W.R., Malencik, D.A., Johnson, C.M., Carr, S.A., Roberts, G.D., Byles, C.E., Anderson, S.R., Heilmeyer, L.M.G., Fischer, E.H. & Crabb, J.W.J. Biol. Chem. 265:11740-11745, 1991). Good recoveries of catalytic activity--with varying degrees of calcium dependence--result upon the digestion of phosphorylase kinase with assorted proteases. However, especially high yields of the chymotryptic fragment are obtainable, with purification on an Ultrogel-34 column and a DEAE Sepharose CL-6B column giving 23% of the maximum possible protein. Physical characterization shows that the 33 kD chymotryptic fragment is globular, with S20,w = 2.9S, and that it has an isoelectric point of 5.3. Our continuous catalytic assay, based on differences in the binding of the fluorescent dye 1-anilinonaphthalene-8-sulfonate by phosphorylase a and b, shows that, on a molar basis, the activity of the fragment is 2.8 fold greater than that of phosphorylase kinase (Malencik, D.A., Zhao, Z. and Anderson, S.R. Biochem. Biophys. Res. Comm. 174: 344-350, 1991). The active fragment also undergoes autophosphorylation. Incubation with Mg[gamma-P32] ATP results in the reaction of 0.7 mol 32P/mol fragment. When the catalytic subunit of the cAMP-dependent protein kinase is also present, the amount of 32P incorporated increases to 1.1 mol/mol. In the former case, phosphorylation occurs primarily at Ser30 while in the latter an additional reaction takes place at Ser81. The phosphopeptides correspond to sequences occurring in the gamma-subunit of phosphorylase kinase.

Amino Acid Sequence↗
PubMed1987

Quantitative histochemical assessment of the heterogeneity of glycogen phosphorylase activity in liver parenchyma of fasted rats using the semipermeable membrane technique and the PAS reaction.

Glycogen phosphorylase (EC 2.4.1.1) has been demonstrated in sections of liver from rats starved for 24 h. The method is based on the measurement of the amount of glycogen formed after incubation in a gelled medium containing glucose 1-phosphate as substrate, using the semipermeable membrane technique. Glycogen was demonstrated with the periodic acid-Schiff (PAS) reaction. Phosphorylase activity appeared to be highest in periportal areas. The optimum substrate concentration for revealing activity of the enzyme was 60-120 mM. After incubation in the absence of substrate, the staining intensity, as measured cytophotometrically as the mean integrated absorbance at 560 nm, was similar to that of an unincubated section. p-Chloromercuribenzoate, a non-specific inhibitor of glycogen phosphorylase activity, reduced the formation of final reaction product attributable to phosphorylase activity completely. The Michaelis constants (KM) of the enzyme in periportal and pericentral areas differed. This was probably due to the presence of the a form only in periportal areas and of the a and b forms in pericentral areas. The mean integrated absorbances in both the periportal and pericentral areas increased linearly with incubation time (4-16 min). A linear relationship was also found with section thickness (4-10 micron). The total activity of glycogen phosphorylase in the periportal areas was double the pericentral activity. It is concluded that the semipermeable membrane technique, combined with the PAS reaction for glycogen, can be used as a valid method for the demonstration and quantification of glycogen phosphorylase activity in livers from starved rats.

Animals↗
PubMed1985

Activities of glycogen synthetase and glycogen phosphorylase in the human endometrium: relative distribution in isolated glands and stroma.

The activities of glycogen synthetase and glycogen phosphorylase were studied in endometrial samples obtained from 51 premenopausal women during the menstrual cycle. The total activities of glycogen synthetase and glycogen phosphorylase and the activity of the active form of glycogen phosphorylase increased gradually from the proliferative phase to the secretory phase and reached a maximum during the midsecretory phase, while the activity of the active form of glycogen synthetase increased slightly. In 30 of the 51 women, the relative distribution of glycogen synthetase and glycogen phosphorylase activities in isolated glands and stromal cells was determined following collagenase digestion of the endometrial specimens. The results indicated that the activities of the active form of glycogen synthetase and glycogen phosphorylase in the isolated glands during the secretory phase were more than threefold and twofold, respectively, greater than those present in the isolated stromal cells and that the levels of these enzymes in the glands and stromal cells changed in parallel with those in the undissociated endometrium observed during the menstrual cycle. In addition, histochemical studies revealed the presence of glycogen phosphorylase activity in both the glands and the stromal cells, whereas the glycogen synthetase activity was present only in the glands. These findings suggest that the stromal cells of the human endometrium as well as the glands may play an important role in the nutrition of the implanting blastocyst.

Cell Separation↗