A physiological role for luteinizing hormone release-inhibiting factor of hypothalamic origin.

A 12 KD peptide, LH release-inhibiting factor (LHRIF), extracted from rat hypothalamus has been shown to inhibit LHRH-stimulated LH release from cultured anterior pituitary cells. In the present study this partially purified material also blocks LHRH-stimulated LH release in pentobarbital-blocked proestrous rats. Administration of a polyclonal antiserum to partially purified LHRIF potentiates estrogen-induced LH release and antagonizes the inhibitory effect of estrogen and progesterone on LH release in ovariectomized rats. These results suggest that a hypothalamic LHRIF plays a physiological role in regulating LH release in the rat.

Partial purification of a hypothalamic factor that inhibits gonadotropin-releasing hormone-stimulated luteinizing hormone release.

A protein that suppresses GnRH-stimulated LH release from dispersed rat anterior pituitary cells was purified from rat hypothalami by chromatography on Sephadex G-25, carboxymethyl cellulose, and high performance gel permeation. The final increase in inhibitory activity was 214-fold. The inhibitor is a glycoprotein with an apparent mol wt of 12,252 +/- 638, as determined by gel permeation on HPLC and electrophoreses as a monomer after treatment with 8 M urea. The inhibitor has a Stokes radius of 16 A, an S value of 2.14 +/- 0.08, an isoelectric point value near 4.1, and a frictional ratio of 1.05. A preliminary amino acid composition is presented.

Studies on interaction between histone V (f2c) and deoxyribonucleic acids.

Histone V (2fc) from chick erythroctes was used in the study of its interaction with DNA from various sources. Complexes between this histone and DNA were formed using the procedure of continuous NaCl gradient dialysis in urea. Two physical methods, namely thermal denaturation and circular dichroism (CD), were used as analytical tools. Thermal denaturation of nucleohistone V with chick or calf thymus DNA shows three melting bands: band I at 45-50 degrees corresponds to free base pairs; band II at 75-79 degrees, and band III at 90-93 degrees correspond to histone-bound base pairs. In histone-bound regions, there are 1.5 amino acid residues/nucleotide in nucleohistone V. In contrast, a value between 2.9 and 3.3 was determined for nucleohistone I (fl) (H. J. Li (1973), Biopolymers 12, 287). Similar melting properties have been observed for histone V complexed with bacterial DNA from Micrococcus luteus. Histone V binding to DNA induces a slight transition from a B-type CD spectrum to a C-type spectrum. Trypsin treatment of nucleohistone V reduces melting band III much more effectively than band II. Such a treatment also restores DNA to B conformation in the free state. Reduction of the melting bands of nucleohistone V by polylysine binding follows the order of I greater than II greater than III, accompanied by the increase of a new band at 100 degrees. When two bacterial DNAs of varied A + T (adenine + thymine) content simultaneously compete for the binding of histone V, the more (A " T)-rich DNA is selectively favored. Under experimental conditions described here, Clostridium perfringens DNA with 69% A + T is bound by histone V in preference to chicken DNA with 56% A + T although the latter has natural sequences for histone V binding.