Change in gonadotropin-binding sites in intracellular organelles and plasma membranes during luteal growth, development and regression

Changes in the gonadotropin-binding sites in plasma membranes and several intracellular organelles of bovine corpora lutea of days 3, 13 and 19 of the cycle were investigated. These three times represent periods of rapid luteal growth (early luteal phase), maturity (mid luteal phase) and the onset of regression (late luteal phase), respectively. The 5'-nucleotidase activity was highest in the fraction possessing a predominance of plasma membranes. It was undetectable in nuclear fractions and detectable to a varying extent in fractions enriched with mitochondria-lysosomes, rough endoplasmic reticulum and Golgi. The gonadotropin-binding sites, as measured by 125I-human choriogonadotropin (hCG) specific binding, were found in all the subcellular organelles. Whereas the affinities remained about the same, the total number of available gonadotropin-binding sites in all the organelles increased from day 3 to 13 and then declined by day 19 of the cycle. Occupancy of binding sites by endogenous luteinizing hormone was not detectable and therefore was unlikely to be responsible for the changes in total number of available binding sites. Thus, binding site changes observed in all the organelles of early, mid and late luteal phase corpora lutea probably reflect actual changes in the steady-state turnover of binding sites. Morphometrically determined relative membrane counts of various subcellular organelles varied with the luteal phase. The relative total gonadotropin-binding sites, calculated from the relative membrane counts and the total number of available binding sites, increased in all the organelles from early to mid and then declined by late luteal phase. Plasma membranes of all three luteal phases contained greater relative total gonadotropin-binding sites than any other single intracellular organelle. However, all the intracellular organelles combined contained 59% of the total luteal cell gonadotropin-binding sites in early luteal phase which decreased to 43 and 28% by mid and late luteal phases respectively.     

Reexamination of Opioid Stimulation of cGMP Formation in Cell Lines of Neuronal Origin

1. The present study reexamines a previous notion on opioid stimulation of cyclic GMP (cGMP) formation and the retraction of the original findings.2. The effect of opioid agonists on cGMP accumulation in two cell lines of neuronal origin was measured. The proportion of cGMP stimulation in NG108-15 neuroblastoma × glioma hybrid cells resembled the proportion of [Ca²⁺]_in elevation by opioids in this culture. The failure of opioids to stimulate cGMP formation in SK-N-SH human neuroblastoma coincided with the lack of cGMP stimulation by other Ca²⁺ mobilizing agents in these cells. The nitric oxide donor nitroprusside elevated cGMP in both cell lines.3. The implication of the opioid-Ca²⁺-NO-cGMP cellular pathway for opioid activity in vivo is discussed.     

Some theoretical considerations on cytosolic redox balance during anaerobiosis in marine invertebrates

Studies on anaerobiosis in marine invertebrates have shown that many rely on malate, octopine, or alanopine dehydrogenases, rather than lactate dehydrogenase, for cytosolic redox balance. These systems were studied by computer simulations with the assumption that these dehydrogenases maintain their substrates and products at instantaneous equilibrium. The simulations permit a study of the redox ratio (NADH/NAD⁺) as a function of the concentration of lactate, malate, or octopine. The redox ratio was found to increase as these products accumulated. It was substantially less in the simulations of malate and octopine dehydrogenases when compared to those of lactate dehydrogenase. This factor may be important for maintaining glycolysis in these organisms, and suggests an advantage for the use of octopine dehydrogenase rather than its analogue lactate dehydrogenase.     

Structural and physicochemical analysis of the reaction between the anti-lysozyme antibody D1.3 and the anti-idiotopic antibodies E225 and E5.2

The reaction between the mouse (BALB/c) anti-idiotiopic monoclonal antibodies E225 and E5.2 and idiotopes on the (BALB/c) anti-lysozyme monoclonal antibody D1.3 has been characterized by titration calorimetry, by equilibrium sedimentation and by the determination of binding association and dissociation rates. The reaction between E5.2 and D1.3 is driven by a large negative enthalpy and its rate and equilibrium association constants are comparable to those observed in other antigen–antibody reactions. In contrast, the reaction between E225 and D1.3 is entropically driven and characterized by slow association kinetic (1 × 10³ M^?1 sec^?1) and a resulting low equilibrium constant (K_a = 2 × 10⁵M ^?1). A correlation of these properties with the three-dimensional structure of the Fab225-FabD1.3 complex, previously determined by X-ray diffraction methods to 2.5 Å resolution, indicates that conformational changes of several D1.3 contacting residues, located in its complementarity determining regions, may explain these features of the reaction.