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Papers by Laurence Jacobs

Molecular and Cellular Biochemistry, 1987

Calcium is necessary for secretion of pituitary hormones. Many of the biological effects of Ca 2+... more Calcium is necessary for secretion of pituitary hormones. Many of the biological effects of Ca 2+ are mediated by the Ca 2+-binding protein calmodulin (CAM), which interacts specifically with proteins regulated by the Ca 2+-CAM complex. One of these proteins is myosin light chain kinase (MLCK), a Ca 2+-calmodulin dependent enzyme that phosphorylates the regulatory light chains of myosin, and has been implicated in motile processes in both muscle and non-muscle tissues. We determined the content and distribution of CaM and CaM-binding proteins in bovine pituitary homogenates, and subcellular fractions including secretory granules and secretory granule membranes. CaM measured by radioimmunoassay was found in each fraction; although approximately one-half was in the cytosolic fraction, CaM was also associated with the plasma membrane and secretory granule fractions. CaM-binding proteins were identified by an lZSI-CaM gel overlay technique and quantitated by densitometric analysis of the autoradiograms. Pituitary homogenates contained nine major CaM-binding proteins of 146, 131, 90, 64, 58, 56, 52, 31 and 22 kilodaltons (kDa). Binding to all the bands was specific, Ca 2+-sensitive, and displaceable with excess unlabeled CaM. Severe heat treatment (100 °C, 15 min), which results in a 75% reduction in phosphodiesterase activation by CaM, markedly decreased ~25I-CaM binding to all protein bands. Secretory granule membranes showed enhancement for CaM-binding proteins with molecular weights of 184, 146, 131, 90, and 52000. A specific, affinity purified antibody to chicken gizzard MLCK bound to the 146 kDa band in homogenates, centrifugal subcellular fractions, and secretory granule membranes. No such binding was associated with the granule contents. The enrichment of MLCK and other CaM-binding proteins in pituitary secretory granule membranes suggests a possible role for CaM and/or CaM-binding proteins in granule membrane function and possibly exocytosis.

The Journal of Cell Biology, 1977

Microtubules assembled in vitro were bound to purified porcine pituitary secretory granules and t... more Microtubules assembled in vitro were bound to purified porcine pituitary secretory granules and to isolated granule membranes. The interaction between microtubules and whole secretory granules was demonstrated by alteration in the sedimentation properties of the microtubules. Incubation of secretory granules with microtubules resulted in pelleting of microtubules which increased as a function of the number of granules added. Binding was quantitated by measurement of the tubulin remaining in the supernate after centrifugation. The interaction of secretory granules and microtubules was inhibited by nucleoside triphosphates and augmented by adenosine 5'-monophosphate and adenosine. When depolymerized protein from microtubules was incubated with secretory granules, the granules did not appear to bind the soluble tubulin dimer present in these preparations. However, the high molecular weight protein associated with microtubules was adsorbed by secretory granules during the binding pr...

Journal of Clinical Investigation, 1973

influence of serum triiodothvronine (T3) and thyroxine (T4) concentrations on the release of prol... more influence of serum triiodothvronine (T3) and thyroxine (T4) concentrations on the release of prolactin in man was studied by determining the prolactin response to synthetic thyrotropin-releasing hormone (TRH) in hypothyroid and hyperthyroid patients before and after correction of their serum thyroid hormone abnormalities. The maximum increment in serum prolactin above the basal level (maximum A prolactin) was used as the index of response to TRH. In 12 patients with primary hypothyroidism, the maximum A prolactin in response to TRH fell from 100.5± 29.1 ng/ml (mean +SEM) before treatment to 36.1±6.0 ng/ml (P < 0.01) during the 4th Nk of treatment with 30 jug T3 + 120 jug T4 daily. The mean serum T3 level increased from 57±8 to 138+10 ngl100 nml! and the mean serum T4 level increased from 3.0±0.4 to 7.2±0.4 Ag/lOO ml during this treatment. In eight normal subjects the maximum Aprolactin in response to TRH was not significantly different during the 4th wk of treatment with 30 Ag T3 + 120 /g T4 daily from the response before treatment. In 10 patients with hvperthyroidism, the maximum Aprolactin in response to TRH increased from 14.2±2.9 ng/ml before treatment to 46.9±6.7 nig/ml (P < 0.001) during antithyroid treatment. The mean serum T3 level fell from 313±47 to 90±8 ng/100 ml, and the mean serum T4 level fell from 20.8±2.5 to 6.8+ 0.6 Ig/100 ml during this treatment. These results show that changes from normal serum levels of T3 and T4 are associated with changes in prolactin responses to TRH; subnormal serum levels of T3 and T4 increase TRH-induced prolactin release,

Journal of Clinical Investigation, 1972

thyrotropin-releasing hormone (TRH) was administered to normal children and hypopituitary patient... more thyrotropin-releasing hormone (TRH) was administered to normal children and hypopituitary patients in a dose of 7 jg/kg i.v. over 30-60 sec. Serum thyrotropin (TSH) and prolactin (HPr) concentrations were measured by radioimmunoassay before and at 15-min intervals for 2 hr after TRH. In 20 normal children HPr rose from a mean baseline value of 7.0±1.2 (SEM) ng/ml to a mean peak value of 39.5±5 ng/ml. In 11 patients with growth hormone (GH) deficiency without TSH deficiency, HPr values rose from a mean baseline of 3.6±0.8 ng/ml to a mean peak value of 13.9+-2.8, a significantly less peak response as compared with normal children (P < 0.005). The TSH responses to TRH, however, were statistically indistinguishable from those of normal children. In 10 patients with GH and TSH deficiency both the mean baseline HPr levels (25.0+5 ng/ml) and the mean peak HPr levels after TRH (68.5+10 ng/ml) were significantly higher (P < 0.005 and < 0.025) than those of normal children. Similar comparisons were also true for the peak TSH responses (P < 0.05). Two panhypopituitary patients released no TSH and only small amounts of HPr after TRH. After thyroid replacement therapy in eight of the patients with GH and TSH deficiency, the mean HPr baseline levels Dr.