Luteal morphology, atresia, and plasma progesterone concentrations during the reproductive cycle of two oviparous lizards, Crotaphytus collaris and Eumeces obsoletus

From ovulation to oviposition, the corpora lutea of the oviparous lizards Crotaphytus collaris and Eumeces obsoletus exhibit three stages of luteal development: 1) luteogenesis, 2) luteal maturity, and 3) luteal regression. Each stage exhibits distinct characteristics, involving changes in: 1) luteal volume, 2) nuclear diameter of cells within the luteal cell mass, and 3) thecal development. Plasma progesterone concentration is greatest during luteogenesis and is positively correlated with ovarian atresia, although atresia occurred throughout the period of gravidity. These data suggest that in these two species, the corpora lutea secrete high amounts of progesterone immediately following ovulation and exhibit morphologically distinct stages of growth and regression.     

Nuclear Overhauser effect studies of the conformations of MgATP bound to the active and secondary sites of muscle pyruvate kinase

MgATP binds both at the active site (site 1) and at a secondary site (site 2) on each monomer of muscle pyruvate kinase as previously found by binding studies and by X-ray analysis. Interproton distances on MgATP bound at each site have been measured by the time-dependent nuclear Overhauser effect in the absence and presence of phosphoenolpyruvate (P-enolpyruvate), which blocks ATP binding at site 1. Interproton distances at site 2 are consistent with a single conformation of bound ATP with a high antiglycosidic torsional angle (chi = 68 +/- 10 degrees) and a C3'-endo ribose pucker (delta = 90 +/- 10 degrees). Interproton distances at site 1, determined in the absence of P-enolpyruvate by assuming the averaging of distances at both sites, cannot be fit by a single adenine-ribose conformation but require the contribution of at least three low-energy structures: 62 +/- 10% low anti (chi = 30 degrees), C3'-endo; 20 +/- 8% high anti (chi = 55 degrees), O1'-endo; and 18 +/- 8% syn (chi = 217 degrees), C2'-endo. Although a different set of ATP conformations might also have fit the interproton distances, the mixture of conformations used also fits previously determined distances from Mn2+ to the protons of ATP bound at site 1 [Sloan, D. L., & Mildvan, A. S. (1976) J. Biol. Chem. 251, 2412] and is similar to the adenine-ribose portion of free Co(NH3)4ATP, which consists of 35% low anti, 51% high anti, and 14% syn [Rosevear, P. R., Bramson, H. N., O'Brian, C., Kaiser, E. T., & Mildvan, A. S. (1983) Biochemistry 22, 3439].(ABSTRACT TRUNCATED AT 250 WORDS)     

8-Hydroxy-5-deazaflavin-reducing hydrogenase from Methanobacterium thermoautotrophicum: 2. Kinetic and hydrogen-transfer studies

Steady-state kinetic parameters have been obtained for the pure 8-hydroxy-5-deazaflavin-reducing hydrogenase. With H2 and 8-hydroxy-5-deazariboflavin (F0) as substrates, Km (H2) = 12 microM, Km (F0) = 26 microM, and Kcat = 225 s-1. In the back-direction, F0H2 is reoxidized (anaerobically) at 225 s-1. Initial velocity patterns, product inhibition patterns, dead-end inhibition by carbon monoxide, and transhydrogenation to Procion Red HE-3B suggest a two-site hybrid ping-pong mechanism. A kinetic derivation for the rate equation is provided in the Appendix. Studies with D2 and with D2O reveal that no steps involving D transfer are substantially rate determining. Further, D2 yields F0H2 with no deuterium at C5 while in D2O a 5-monodeuterio F0H2 product is formed, indicating complete exchange of hydrogens from H2 with solvent before final transfer of a hydride ion out from reduced enzyme to C5 of F0.     

Synthetic peptides used to locate the alpha-bungarotoxin binding site and immunogenic regions on alpha subunits of the nicotinic acetylcholine receptor

Synthetic peptides corresponding to 57% of the sequence of alpha subunits of acetylcholine receptors from Torpedo californica electric organ and extending from the NH2 to the COOCH terminus have been synthesized. The alpha-bungarotoxin binding site on denatured alpha subunits was mapped within the sequence alpha 185-199 by assaying binding of 125I-alpha-bungarotoxin to slot blots of synthetic peptides. Further studies showed that residues in the sequence alpha 190-194, especially cysteines-alpha 192, 193, were critical for binding alpha-bungarotoxin. Reduction and alkylation studies suggested that these cysteines must be disulfide linked for alpha-bungarotoxin to bind. Binding sites for serum antibodies to native receptors or alpha subunits were mapped by indirect immunoprecipitation of 125I-peptides. Several antigenic sequences were identified, but a synthetic peptide corresponding to the main immunogenic region (which is highly conformation dependent) was not identified.     

Saccharomyces cerevisiae positive regulatory gene PET111 encodes a mitochondrial protein that is translated from an mRNA with a long 5'' leader.

The yeast nuclear gene PET111 is required specifically for translation of the mitochondrion-coded mRNA for cytochrome c oxidase subunit II. We have determined the nucleotide sequence of a 3-kilobase segment of DNA that carries PET111. The sequence contains a single long open reading frame that predicts a basic protein of 718 amino acids. The PET111 gene product is a mitochondrial protein, since a hybrid protein which includes the amino-terminal 154 amino acids of PET111 fused to beta-galactosidase is specifically associated with mitochondria. PET111 is translated from a 2.9-kilobase mRNA which, interestingly, has an extended 5'-leader sequence containing four short open reading frames upstream of the long open reading frame. These open reading frames exhibit an interesting pattern of overlap with each other and with the PET111 reading frame.     

Deletions within the amino-terminal half of the c-src gene product that alter the functional activity of the protein.

To examine how amino acid sequences outside of the catalytic domain of pp60c-src influence the functional activity of this protein, we have introduced deletion mutations within the amino-terminal half of pp60c-src. These mutations caused distinct changes in the biochemical properties of the c-src gene products and in the properties of cells infected with retroviruses carrying these mutant c-src genes. Cells expressing the c-srcNX protein, which contains a deletion of amino acids 15 to 89, displayed a refractile, spindle-shaped morphology, formed intermediate-sized, tightly packed colonies in soft agar, and contained elevated levels of cellular phosphotyrosine-containing proteins. Thus, deletion of amino acids 15 to 89 can activate the kinase activity and transforming potential of the c-src gene product. Deletion of amino acids 112 to 225, however, did not increase the kinase activity or transforming ability of pp60c-src; indeed, deletion of these sequences in c-srcHP suppressed phenotypic alterations induced by pp60c-src. Cells expressing the c-srcNP or c-srcBS gene products (containing deletions of amino acids 15 to 225 and 55 to 169, respectively) displayed a fusiform, refractile morphology and formed diffuse colonies in soft agar; the mutant proteins displayed an increased in vitro protein-tyrosine kinase activity. However, only a few cellular proteins contained elevated levels of phosphotyrosine in vivo. Thus, deletions downstream of amino acid 89 severely restricted the ability of c-src to phosphorylate cellular substrates in vivo without affecting the intrinsic tyrosine kinase activity of the c-src gene product. These results suggest the existence of at least two modulatory regions within the amino-terminal half of pp60c-src that are important for the regulation of tyrosine kinase activity and for the interaction of pp60c-src with cellular substrates.     

Substitution of an invariant nucleotide at the base of the highly conserved ''530-loop'' of 15S rRNA causes suppression of yeast mitochondrial ochre mutations.

We have determined the nucleotide sequence alteration in the 15S rRNA gene of a Saccharomyces cerevisiae strain carrying the previously described mitochondrial ochre suppressor, MSUI. The suppressor contains an A residue at position 633 of the yeast mitochondrial sequence, in place of the wild-type G. This position, located in the highly conserved region forming the stem of the '530-loop', corresponds to G517 of the Escherichia coli 16S rRNA and is occupied by G in all other known small rRNA sequences. This finding strongly supports the previous conclusions of others that the 530-loop region plays an important role in enhancing translational accuracy.     

Fluorescence lifetime studies with staphylococcal nuclease and its site-directed mutant. Test of the hypothesis that proline isomerism is the basis for nonexponential decays.

Using frequency domain methods, the fluorescence decay of Trp-140 in staphylococcal nuclease and its site-directed mutant (Pro-117----Gly) has been examined. Based on nuclear magnetic resonance (NMR) studies (Evans, P. A., C. M. Dobson, R. A. Kautz, G. Hatfull, and R. O. Fox. 1987. Nature [Lond.]. 329:266-268), it is believed that nuclease exists in two macroscopic, native conformations and that the slow interconversion of these conformations is controlled by the cis----trans isomerization of Pro-117. The above mutant shows only one native conformation in NMR experiments. To test the hypothesis that the biexponential fluorescence decay of Trp-140 of nuclease can also be related to the existence of these conformational states of the protein, we have compared the decay patterns of the wild type and mutant. Essentially no difference was observed, which indicates that there is some other basis for the nonexponential decay of Trp-140. We have used global nonlinear least squares analysis to link the fit of data at several temperatures.