Identification of spectrin as a calmodulin-binding component in the pituitary gonadotrope

Miscellaneous · Sun Jan 01 00:00:00 EST 1989

OSTI ID:5545320

Wooge, C H

Gonadotropin releasing hormone (GnRH) is a hypothalamic decapeptide which stimulates the release of luteinizing hormone (LH) and follicle stimulating hormone (FSH) from the pituitary. Ca{sup 2+} fulfills the requirements of a second messenger for this system. Inhibition of calmodulin will inhibit GnRH stimulated LH release. The aim of the present studies has been to identify the locus of action of calmodulin within the pituitary. By use of an {sup 125}I-calmodulin gel overlayer assay, five major Ca{sup 2+}-dependent {sup 125}I-calmodulin labelled components of subunit M{sub r} > 205,000; 200,000; 135,000; 60,000; and 52,000 have been identified. This labeling was found to be phenothiazine-sensitive. Ca{sup 2+}-independent binding that was observed appears to be due to hydrophobic interactions of calmodulin with acid-soluble proteins, principally histones. Subcellular fractionation revealed that the Ca{sup 2+}-dependent calmodulin-binding components are localized primarily in the cytosolic fraction. Separation of dispersed anterior pituitary cells through a linear Metrizamide gradient yielded gonadotrope-enriched fractions, which were found to contain all five {sup 125}I-calmodulin binding components corresponding to the major bands in the pituitary homogenate. The calmodulin-binding component levels do not appear to be differentially regulated by steroids. The calmodulin binding component with a M{sub r} > 205,000 has been identified as spectrin. Spectrin-like immunoreactivity and {sup 125}I-calmodulin-binding activity in pituitary tissue homogenates co-migrated in various percentage acrylamide gels with avian erythrocyte spectrin. Spectrin was detected in a gonadotrope-enriched fraction by immunoblotting, and confirmed in gonadotropes by indirect immunofluorescence of cultured pituitary cells in which spectrin- and LH-immunoreactivity co-localized.

• Research Organization: Iowa Univ., Iowa City, IA (United States)
• OSTI ID: 5545320
• Resource Relation: Other Information: Thesis (Ph. D.)
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
CALMODULIN
BIOCHEMICAL REACTION KINETICS
PITUITARY GLAND
BIOCHEMISTRY
PROTEINS
RADIOASSAY
CALCIUM COMPOUNDS
FRACTIONATION
GONADOTROPINS
IODINE 125
LH
TRACER TECHNIQUES
ALKALINE EARTH METAL COMPOUNDS
BETA DECAY RADIOISOTOPES
BODY
CHEMISTRY
DAYS LIVING RADIOISOTOPES
ELECTRON CAPTURE RADIOISOTOPES
ENDOCRINE GLANDS
GLANDS
HORMONES
INTERMEDIATE MASS NUCLEI
INTERNAL CONVERSION RADIOISOTOPES
IODINE ISOTOPES
ISOTOPE APPLICATIONS
ISOTOPES
KINETICS
NUCLEI
ODD-EVEN NUCLEI
ORGANIC COMPOUNDS
ORGANS
PEPTIDE HORMONES
PITUITARY HORMONES
RADIOISOTOPES
REACTION KINETICS
SEPARATION PROCESSES
550201* - Biochemistry- Tracer Techniques