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Biomedical subjects

H R Kaslow

Publications and source records attributed to H R Kaslow.

48 records · Page 3Linked to original sources
PubMed1980

Defect of receptor-cyclase coupling protein in pseudohypoparathyroidism.

Hormone-sensitive adenylate cyclase contains a recently discovered protein component that is required for stimulation of cyclic AMP synthesis by hormones and guanine nucleotides; the component presumably couples the membrane receptor to the cyclase. We studied this protein (termed "N") in erythrocyte membranes of patients with pseudohypoparathyroidism, using assays of the protein's biochemical activity and of its susceptibility to radiolabeling in the presence of [32P]NAD and cholera toxin. By both assays, the protein's activity was reduced by 40 to 50 per cent in erythrocytes of five of 10 patients with Type I pseudohypoparathyroidism as compared with those of normal and hypoparathyroid subjects and one patient with Type II pseudohypoparathyroidism. If activity of the N protein is reduced in other tissues, this deficiency could cause the resistance of target organs in pseudohypoparathyroidism to parathyroid hormone and other hormones that work via cyclic AMP. Erythrocytes of five patients with Type I pseudohypoparathyroidism, all in one family, showed no defect in activity of the N protein; the biochemical defect of this family remains undefined.

Adenylyl Cyclases↗
PubMed1979

Interconversion between multiple glucose 6-phosphate-dependent forms of glycogen synthase in intact adipose tissue.

We have tested the hypothesis that interconversion between multiple glucose-6-P-dependent forms of glycogen synthase helps regulate glycogen synthesis in adipose tissue. Our results indicate that interconversion of glycogen synthase in adipose tissue involves primarily dependent forms and that these interconversions were measured better by monitoring the activation constant (A0.5) for glucose-6-P than measuring the -: + glucose-6-P activity ratio. Insulin decreased and epinephrine increased the A0.5 for glucose-6-P without significant change in the activity ratio. Insulin consistently decreased the A0.5 in either the presence or absence of glucose, indicating that the insulin-promoted interconversion did not require increased hexose transport. Isoproterenol increased the A0.5 for glucose-6-P, while methoxamine was without effect, indicating beta receptors mediate adrenergic control of interconversion between glucose-6-P-dependent forms. The changes in the A0.5 produced by incubations with insulin or epinephrine were mutually reversible. We conclude that 1) glycogen synthesis in adipose tissue is catalyzed by multiple glucose-6-P-dependent forms of glycogen synthase, 2) hormones regulate glycogen metabolism by promoting reversible interconversions between these forms, and 3) there is no evidence that a glucose-6-P-independent form of glycogen synthase exists in intact adipose tissue.

Adipose Tissue↗
PubMed1979

Adaptations of glycogen metabolism in rat epididymal adipose tissue during fasting and refeeding.

It is well documented that adipose tissue glycogen content decreases during fasting and increases above control during refeeding. We now present evidence that these fluctuations result from adaptations intrinsic to adipose tissue glycogen metabolism that persist in vitro: in response to insulin (1 milliunit/ml), [3H]glucose incorporation into rat fat pad glycogen was reduced to 10% of control after a 3-day fast; incorporation increased 6-fold over fed control on the 4th day of refeeding following a 3-day fast. We have characterized this adaptation with regard to alterations in glycogen synthase and phosphorylase activity. In addition, we found that incubation of fat pads from fasted rats with insulin (1 milliunit/ml) increased glucose-6-P content, indicating that glucose transport was not the rate-limiting step for glucose incorporation into glycogen in the presence of insulin. In contrast, feeding a fat-free diet resulted in dramatic increases in glycogen content of fat pads without a concomitant increase in glucose incorporation into glycogen in response to insulin (1 milliunit/ml). Thus, fasting and refeeding appeared to alter insulin action on adipose tissue glycogen metabolism more than this dietary manipulation.

Adipose Tissue↗
PubMed1978

Genetic evidence that cholera toxin substrates are regulatory components of adenylate cyclase.

Cholera toxin, using [32P]NAD+ as substrate, specifically radiolabels at least two proteins in plasma membranes of wild type S49 mouse lymphoma cells. The toxin-specific substrates are detectable by sodium dodecyl sulfate-polyacrylamide gel electrophoresis as bands corresponding to molecular weights of 45,000 and a doublet of 52,000 to 53,000. Membranes of two other cell types exhibit similar patterns of radiolabeled bands specifically produced by incubation with cholera toxin: the "uncoupled" variant S49 cell, which possesses adenylate cyclase activity unresponsive to hormones, and the HTC4 rat hepatoma cell, which lacks detectable catalytic adenylate cyclase activity but contains components of the cyclase system necessary for regulation by guanyl nucleotides and NaF. Little or no toxin-specific radiolabeling is observed in membranes of a fourth cell type, the adenylate cyclase activity-deficient S49 variant, which functionally lacks components of the cyclase system involved in cholera toxin action and regulation by guanyl nucleotides and NaF. The toxin-specific labeling pattern is not observed in membranes prepared from wild type S49 cells previously treated with cholera toxin in culture. One or both of the toxin substrates thus appears to be involved in regulation of adenylate cyclase by guanyl nucleotides and fluoride ion.

Adenylyl Cyclases↗
PubMed1978

Reconstitution of cholera toxin-activated adenylate cyclase.

Reconstitution of adenylate cyclase activity responsive to stimulation by guanylyl-5'imidodiphosphate or NaF may be achieved by mixing dilute Lubrol 12A9-solubilized extracts of wild-type S49 membranes with membranes of an adenylate cyclase-deficient variant. Experiments using N-ethylmaleimide to inactivate components of the adenylate cyclase system indicate that distinct components from both wild-type detergent extracts and adenylate cyclase-deficient membranes are essential for reconstitution. These results and conclusions confirm those of E. M. Ross and A. G. Gilman [J. Biol. Chem. (1977) 252, 6966-6969]. Detergent extracts of cholera toxin-treated wild-type membranes yield a reconstituted adenylate cyclase as responsive to GTP as to guanylyl-5'-imidodiphosphate whereas, in the absence of cholera toxin treatment, GTP has little or no effect. Cholera toxin-treated adenylate cyclase-deficient membranes and Lubrol 12A9 extracts from them, however, fail to yield a reconstituted adenylate cyclase that responds to GTP with an increase in cyclase activity. Because treatment of the adenylate cyclase-deficient variants with cholera toxin is without effect on the reconstituted cyclase, we propose that the cholera toxin substrate is absent or altered in the adenylate cyclase-deficient phenotype.

Adenylyl Cyclase Inhibitors↗
PubMedDate not supplied

CTX-B inhibits CTL cytotoxicity and cytoskeletal movements.

Binding of cytotoxic T lymphocytes (CTL) to specific targets induces cytoskeletal movements in the effector cell followed by delivery of the lethal hit which ultimately results in target cell lysis. The question whether movement of the cytoskeleton in CTL are obligatory for delivery of the lethal hit is not resolved. Here we report that the CTX-B subunit of cholera toxin which is devoid of the catalytic CTX-A subunit inhibits CTL function. Inhibition was found not to be due to interference with TCR expression, CTL-target conjugate formation, target induced transmembrane signalling or secretion of BLT-esterase. CTX-B however does interfere with F-actin patch formation at the effector target binding site and inhibits reorientation of the microtubule organizing center and Golgi apparatus towards the target binding site. It is concluded that interference with cytoskeletal movements is responsible for inhibition of cytolysis pointing to an important role of the cytoskeleton in the lytic reaction.

Actins↗