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Biomedical subjects

Z Ahmad

Publications and source records attributed to Z Ahmad.

72 records · Page 4Linked to original sources
PubMed1983

Multiple phosphorylation of rabbit skeletal muscle glycogen synthase. Evidence for interactions among phosphorylation sites and the resolution of electrophoretically distinct forms of the subunit.

Phosphorylation of rabbit skeletal muscle glycogen synthase by a cyclic nucleotide and Ca2+-independent protein kinase, PC0.7, caused the enzyme to be a better substrate for phosphorylation by another cyclic nucleotide and Ca2+-independent protein kinase, FA/GSK-3. In contrast, phosphorylation by the combination of FA/GSK-3 and cyclic AMP-dependent protein kinase led to less phosphorylation than predicted from the individual actions of the protein kinases. These results are explained in part by the existence of cooperative interactions among the phosphorylation sites of glycogen synthase. Phosphorylation by FA/GSK-3 also correlated with a reduction in the electrophoretic mobility, in the presence of sodium dodecyl sulfate, of the glycogen synthase subunit from an apparent molecular weight of 85,000-86,000 to values of 88,000 and ultimately 90,000. The synergistic phosphorylation by PC0.7 and FA/GSK-3 was associated with an increased formation of the species of reduced electrophoretic mobility. The effects on subunit mobility were also reflected in the behavior of a larger phosphorylated CNBr fragment of glycogen synthase, CB-2, which gave apparent molecular weights of 22,000-27,000 depending on its phosphorylation state.

Animals↗
PubMed1982

Rabbit liver glycogen synthase kinases. Characterization of a protein kinase (PC0.7) able to phosphorylate glycogen synthase and phosvitin.

A rabbit liver protein kinase (PC0.7), able to phosphorylate glycogen synthase and phosvitin, has been extensively purified. The enzyme had apparent Mr = 170,000-190,000 as judged by gel filtration and was associated with two major polypeptide species, alpha (Mr = 43,000) and beta (Mr = 25,000). Two other polypeptides, Mr = 38,000 and Mr = 35,000, were also detected. Treatment with trypsin led to an enzyme composed only of polypeptides of Mr = 35,000 and Mr = 25,000. The beta-polypeptide underwent autophosphorylation when incubated with Mg2+ and ATP or GTP. The protein kinase was effective in utilizing both ATP and GTP as the phosphoryl donor (apparent Km values 5-11 microM and 9-19 microM, respectively). The enzyme phosphorylated phosvitin, casein, and glycogen synthase but not histone or phosphorylase and was inhibited by heparin. Phosphorylation of glycogen synthase proceeded to approximately 0.5 phosphate/subunit with little inactivation of the glycogen synthase. The phosphorylation occurred predominantly in a 21,000-dalton CNBr fragment of glycogen synthase that had been previously shown to reside toward the COOH terminus of the molecule. The liver PC0.7 appeared very similar to an analogous enzyme isolated from rabbit muscle (DePaoli-Roach, A. A., Ahmad, Z., and Roach, P. J. (1981) J. Biol. Chem. 256, 8955-8962). The present work, therefore, provides a point of contact between the Ca2+ and cyclic nucleotide-independent glycogen synthase kinases of rabbit liver and muscle.

Animals↗
PubMed1981

Characterization of a rabbit skeletal muscle protein kinase (PC0.7) able to phosphorylate glycogen synthase and phosvitin.

A protein kinase (designated PC0.7 in DePaoli-Roach, A. A., Roach, P. J., and Larner, J. (1979) J. Biol. Chem. 254, 12062-12068) that phosphorylated both glycogen synthase and phosvitin, has been extensively purified from rabbit skeletal muscle, close to apparent homogeneity. The enzyme activity was associated with two polypeptides, alpha (Mr = 43,000) and beta (Mr = 25,000), present in approximately equimolar amounts. The apparent molecular weight of the enzyme was 180,000, as determined by gel filtration, and 130,000, as judged from sucrose density gradient sedimentation. Unless precautions were taken during the purification, the alpha polypeptide underwent degradation, probably as a result of protease action. The beta polypeptide itself could be phosphorylated upon incubation of the enzyme with ATP and Mg2+ but no significant change in activity accompanied this phosphorylation reaction. The protein kinase was effective in utilizing both ATP and GTP as phosphate donors, with apparent Km values of 13 microM and 20-35 microM, respectively. The apparent Km values for phosvitin and glycogen synthase were 15 microM and greater than 10 microM, respectively. PC0.7 phosphorylated glycogen synthase to a level of approximately 0.5 phosphate/subunit, with little inactivation of the glycogen synthase. Phosphorylation occurred predominantly in a 21,000-dalton cyanogen bromide fragment of glycogen synthase, the same fragment preferentially phosphorylated by cyclic AMP-dependent protein kinase. This phosphorylation was also located in an approximately 17,000-dalton COOH-terminal region of the glycogen synthase molecule that is removed by limited tryptic proteolysis. Phosphorylation of glycogen synthase by PC0.7 occurred at serine residues whereas in phosvitin both serine and threonine residues were modified by PC0.7 action.

Animals↗
PubMed1981

Dephosphorylation of rabbit skeletal muscle glycogen synthase (phosphorylated by cyclic AMP-independent synthase kinase 1) by phosphatases.

Phosphorylation of rabbit skeletal muscle glycogen synthase by cyclic AMP-independent synthase kinase 1 results in the incorporation of 4 mol of PO4/subunit. Incubation of the phosphorylated synthase with rabbit muscle phosphoprotein phosphatase brings about the hydrolysis of phosphates from all four major tryptic peptides and an increase in the synthase activity ratio from 0.01 to 0.85. Incubation of the phosphorylated synthase with calf intestinal alkaline phosphatase brings about the preferential hydrolysis of phosphates from three of the four major tryptic peptides and a slight increase in the four major tryptic peptides and a slight increase in the synthase activity ratio from 0.01 to 0.1. The phosphorylation site which is resistant to hydrolysis by calf intestinal alkaline phosphatase can be dephosphorylated by subsequent incubation with rabbit muscle phosphoprotein phosphatase. This dephosphorylation is accompanied by an increase in the synthase activity ratio to approximately 0.9. Measurements of the changes in the kinetic properties of the synthase samples dephosphorylated by alkaline phosphatase reveal that the phosphorylation sites susceptible to hydrolysis by alkaline phosphatase mainly affect the binding of glucose-6-P to the synthase. Comparison of the kinetic properties of the synthase samples dephosphorylated by alkaline phosphatase and by phosphoprotein phosphatase we find that the phosphorylation site resistant to hydrolysis by alkaline phosphatase affects both the binding of UDP-glucose and glucose-6-P to the synthase.

Alkaline Phosphatase↗
PubMed1981

Evaluation of five immunodiagnostic techniques in echinococcosis patients.

Double diffusion (DD), indirect haemagglutination (IHA), immunoelectrophoresis (IEP), latex agglutination (LA), and complement fixation (CF) tests were evaluated for sensitivity and specificity in the diagnosis of 141 surgically-proven Turkana echinococcosis patients and 10 controls. The overall sensitivities for the tests were: IHA, 86.7%; LA, 53.3%; CF, 63.3%; DD, 55.0%; IEP, 55.0%. LA and CF tests produced a high number of false positive results; IHA gave a false positive result in 10% of cases; no false positives were obtained with IEP and DD. A combination of the latter three tests would therefore offer the best chance of detecting specific anti-Echinococcus antibodies, with an average sensitivity of 62.7%. The possible reasons for the relatively high incidence of false negative values are discussed.

Animals↗
PubMed1979

Clomiphene-induced pregnancy in a patient with diabetes insipidus and hypothyroidism.

A patient with diabetes insipidus and hypothyroidism developed anovular menstrual cycles. Ovulation, which was followed by pregnancy, was induced by the administration of clomiphene. In the later stages of pregnancy, an increase in the dosage of vasopressin was necessary to achieve a satisfactory control of the symptoms of diabetes insipidus. Labour was induced before the estimated date of confinement by the intravenous administration of oxytocin and an intra-partum haemorrhage necessitated delivery by the lower-segment caesarean section. The post-partum period was uneventful. Lactation was suppressed on request from the patient.

Adult↗
PubMedDate not supplied

Immunohistochemical localization of ECE-1 in the human placenta.

Over the last several years, endothelin (ET-1) has emerged as an important mediator in the pathogenesis of pre-eclampsia and preterm labour, as well as in the normal function of gestational tissues. While the distribution of ET and its binding sites in the human placenta have been well studied, much less has so far been reported about the distribution of placental ET-1 processing enzymes. By immunohistochemical analysis and immunofluorescence, endothelin-converting enzyme-1 (ECE-1), the enzyme that synthesizes ET-1, is localized to five distinct cell populations in the human placenta: (1) the endothelial cells lining the maternal basal plate blood vessels, (2) the intermediate trophoblasts, (3) the endothelial cells lining the chorionic villous blood vessels, (4) the chorionic villous stromal cells and (5) the chorionic villous trophoblasts. The localization of ECE-1 corresponds with the previously reported distribution of ET-1 in the human placenta and is in accordance with the function of this enzyme in regulating vascular tone through synthesis of ET-1. The abundance of ECE-1 in the basal plate is consistent with a second possible function of this enzyme in affecting uterine contractions. ECE-1 may serve as a target for prognosis and therapy in states of pathologically altered vascular tone and/or altered myometrial smooth muscle tone in gestation.

Adult↗
PubMedDate not supplied

Plasma renin activity and plasma aldosterone concentrations in untreated Nigerians with essential hypertension.

On the basis of existing information we set out to test an hypothesis that 'the blood volume and more specifically total body sodium and sodium disposition in the body play a more important role in blood-pressure regulation and the pathophysiology of hypertension than other regulatory mechanisms in the indigenous African'. To achieve our objective, ninety-eight newly diagnosed unmedicated hypertensives with adequate renal function were admitted to the study. Fifty-one (52%) of the subjects were males while forty-seven (48%) were females. Their ages ranged between 21 and 70 years. All grades of the disease were adequately represented with thirty (31%) being mild, fifty (51%) moderate and eighteen (18.4%) in severe phase of the disease. Blood-pressure measurements and blood samples were obtained in the supine position in all the patients after adequate preparation. Plasma renin activity (PRA) and plasma aldosterone concentrations were measured by specific radioimmunoassays. Contrary to what obtains elsewhere, seventy-six (77%) of our patients were of the low renin status, twelve (12%) of whom had undetectable levels by our assay system. Eighteen (18.4%) had PRA levels in the medium range and five (5.1%) in the high range. In a cohort, forty-two (43%) of our ninety-eight patients, we estimated plasma aldosterone levels. The results obtained showed that the plasma aldosterone concentrations were significantly higher in hypertensives than in our normal controls (P less than 0.01). There was lack of correlation between PRA or plasma aldosterone when compared to mean arterial pressure or serum Na+. These results are discussed in relation to the management of hypertension in our environment.

Adult↗