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Biomedical subjects

A R Means

Publications and source records attributed to A R Means.

At least 199 records · Page 11Linked to original sources
PubMed1981

Factors affecting Sertoli cell function in the testis.

The Sertoli cell is the primary target for FSH action in the mammalian testis. These cells contain the majority of testicular plasma membrane receptors for this hormone. Receptor occupancy is directly correlated with a stimulation of adenylyl cyclase and a decrease in the activity of a cytoplasmic Ca++-sensitive cAMP phosphodiesterase. Regulation of these two enzymes allows increased intracellular accumulation of cAMP, activation of cAMP-dependent protein kinase and phosphorylation of a variety of protein substrates. All of these events occur within the first 30 min following exposure of isolated Sertoli cells to FSH. RNA and protein synthesis are also enhanced by FSH. Previous studies have suggested that this gonadotropin may augment the overall cellular synthesis of proteins. Our results reveal that protein kinase inhibitor (PKI) is selectively elevated by FSH both in vivo and in vitro. PKI thus becomes the initial intracellular protein whose synthesis is under FSH control. In addition to effects on protein synthesis, FSH also positively modulates the secretion of several specific proteins. One of the proteins in this latter category is androgen binding protein (ABP). Again, regulation can be observed both in vivo and in vitro. Elevated synthesis of PKI occurs prior to demonstrable secretion of ABP. Both of these events occur subsequent to the effects of FSH on cAMP metabolism. Indeed cAMP (or any of several nonhydrolyzable derivatives) can substitute for FSH in vitro. The temporal sequence of events subsequent to hormone binding and cAMP production are identical, but occur more rapidly. Together these data support the hypothesis that most of the biochemical steps leading to the synthesis and secretion of proteins by FSH are regulated by elevated levels of cAMP.

Adenylyl Cyclases↗
PubMed1980

Amino acid sequence of the signal peptide of apoVLDL-II, a major apoprotein in avian very low density lipoproteins.

ApoVLDL-II is a major apoprotein in avian very low density lipoproteins (Jackson, R. L., Lin, H.-Y., Chan, L., and Means, A.R. (1977) J. Biol. Chem. 252, 250-253). Partially purified apoVLDL-II mRNA was translated in vitro in a wheat germ system in the presence of various labeled amino acids. The product, designated preapoVLDL-II, was purified by immunoprecipitation and sodium dodecyl sulfate acrylamide gel electrophoresis. It was subjected to automated Edman degradation in a Beckman Sequencer. The signal peptide was found to be a 23-amino acid NH2-terminal extension of the mature protein with the following sequence: Met-Gln-Tyr-Arg-Ala-Leu-Val-Ile-Ala-Val-Ile-Leu-Leu-Leu-Ser-Thr-Val-Pro-Glu-Val-Cys-Ser-Lys where Lys is the NH2-terminal residue of mature apoVLDL-II. The abundance and distribution of the hydrophobic amino acid residues are very similar to those of other signal sequences and the average hydrophobicity for the 23 residues is -1227 cal/mol/residue. However, translocation of preapoVLDL-II would represent a unique case of vectorial migration of a protein through a membrane since apoVLDL-II is itself an apolipoprotein and binds lipid spontaneously.

Amino Acid Sequence↗
PubMed1980

Crystallization and preliminary X-ray investigation of calmodulin.

Crystals of rat testis calmodulin, a multifunctional Ca2+-binding protein have been grown from solutions of 2-methyl-2,4-pentanediol. The crystals are triclinic, space group P1, with a = 29.79(4) A, b = 53.74(7) A, c = 24.78(3) A, alpha = 93.46(2)degrees, beta = 96.98(2)degrees, and gamma = 89.05(3)degrees. There is 1 calmodulin molecule per unit cell. The crystals are quite stable to x-rays and diffract beyond 2.5 A resolution.

Animals↗
PubMed1980

Calmodulin--an intracellular calcium receptor.

Calmodulin, a protein that binds calcium with high affinity and specificity, is structurally conserved and functionally preserved throughout the animal and plant kingdoms. It serves as an intracellular Ca2+-receptor and mediates the Ca2+ regulation of cyclic nucleotide and glycogen metabolism, secretion, motility and Ca2+ transport. Calmodulin is also a dynamic component of the mitotic apparatus.

Animals↗
PubMed1980

Protein inhibitor of cAMP-dependent protein kinase: production and characterization of antibodies and intracellular localization.

Multiple forms of protein kinase inhibitor exist in mammalian testis. Specific antibodies to testicular protein kinase inhibitor (PKI) have been raised in sheep. The antibody to the smallest of the inhibitors (9300 daltons) has been purified by antigen-affinity chromatography and shown to give a precipitin band with the inhibitor by double immunodiffusion. The antibody does not recognize any of the subunits of cyclic nucleotide-dependent protein kinases, namely cGMP-dependent protein kinase or the catalytic or regulatory subunits from type I or type II cAMP-dependent protein kinases. The biological activity of the 9300 dalton PKI is blocked completely by a 5 fold molar excess of antibody. Furthermore, the antibody can also block the activity of all other forms of testicular PKI. Using the antibody in indirect immunofluorescence microscopy, PKI localization was examined during interphase and mitosis in a variety of cell types. Our observations indicate that PKI is localized on microtubules in the cytoplasmic microtubule complex during interphase and in the spindle apparatus during mitosis. We suggest that PKI may play a role in the cAMP-dependent regulation of microtubule structure and/or function.

Animals↗
PubMed1980

Ovomucoid intervening sequences specify functional domains and generate protein polymorphism.

Two thirds of the natural chicken ovomucoid gene has been sequenced, including all exons and the intron sequences surrounding all fourteen intron/exon junctions. The junction sequences surrounding four of the introns are redundant; however, the sequences surrounding the other three introns contain no redundancies and thus the splicing sites at either end of these three introns are unambiguous. The splicing in all cases conforms to the GT-AG rule. The ovomucoid gene sequence around intron F can be used to predict the cause of an internal deletion polymorphism in the ovomucoid protein, which is an apparent error in the processing of the ovomucoid pre-mRNA. We also compare the structural organization of the ovomucoid gene with the ovomucoid protein sequence to examine theories of the evolution of ovomucoids as well as the origin of intervening sequences. This analysis suggests that the present ovomucoid gene evolved from a primordial ovomucoid gene by two separate intragenic duplications. Furthermore, sequence analyses suggest that introns were present in the primordial ovomucoid gene before birds and mammals diverged, about 300 million years ago. Finally, the positions of the introns within the ovomucoid gene support the theory that introns separate gene segments that code for functional domains of proteins and provide insight on the manner by which eucaryotic genes were constructed during the process of evolution.

Animals↗
PubMed1980

Calmodulin in endocrine cells and its multiple roles in hormone action.

Calmodulin interaction with Ca2+ may present a receptor mechanism analogous to the association of steroid hormones with cytoplasmic receptor proteins. In the systems examined to date, neither calmodulin nor Ca2+ alone have stimulatory effects. We have attempted to illustrate the similarities between the regulation of cellular events by Ca2+-calmodulin and the cyclic nucleotide system. If a general mechanism for calmodulin can be predicted it is to activate various enzymes to phosphorylate target proteins in a Ca2+-dependent manner. It is also of interest to point out the coorindate regulation of protein phosphorylation by Ca2+ and cAMP. Calmodulin can be considered to be involved in both types of reactions. This Ca2+-receptor not only activates Ca2+-dependent protein kinases directly but also plays an indirect role in cAMP-dependent phosphorylation by participating in the regulation of the intracellular steady-state levels of cAMP. The importance of calmodulin as a Ca2+-receptor and as a modulator of hormone action and endocrine cells illustrates the pleiotypic nature of this protein in both cellular and molecular aspects of endocrinology.

Adenosine Triphosphatases↗
PubMed1980

Localization of calmodulin in rat cerebellum by immunoelectron microscopy.

Calmodulin, a multifunctional Ca(++)-binding protein, is present in all eucaryotic cells. We have investigated the distribution of this protein in the rat cerebellum by immunoelectron microscopy using a Fab-peroxidase conjugate technique. In Purkinje and granular cell bodies, calmodulin reaction product was found localized both on free ribosomes and on those attached to rough endoplasmic reticulum (RER) and the nuclear envelope. No calmoduline was observed in the cisternae of RER or the Golgi apparactus. Calmodulin did not appear to be concentrated in the soluble fraction of the cell under the conditions used. Rather, peroxidase reaction product could be seen associated with membranes of the Golgi apparatus the smooth endoplasmic reticulum (SER), and the plasma membrane of both cell bodies and neuronal processes. In the neuronal dendrites, calmodulin appeared to be concentrated on membranes of the SER, small vesicles, and mitochondria. Also, granular calmodulin was observed in the amorphous material. In the synaptic junction, a large amount of calmodulin was seen attached to the inner surface of the postsynaptic membrane, whereas very little was observed in the presynaptic membrane or vesicles. These observations suggest that calmodulin is synthesized on ribosomes and discharged into the cytosol, and that it then becomes associated with a variety of intracellular membranes. Calmodulin also seems to be transported via neuronal processes to the postsynaptic membrane. Calmodulin localization at the postsynaptic membrane suggests that this protein may mediate calcium effects at the synaptic junction and, thus, may play a role in the regulation of neurotransmission.

Animals↗
PubMed1980

Primary sequence of ovomucoid messenger RNA as determined from cloned complementary DNA.

Ovomucoid messenger RNA (mRNAom) comprises approximately 8% of the total mRNA in the estrogen-stimulated oviduct. The recombinant plasmid pOM100 contained DNA complementary to the 3' end of mRNAom. DNA complementary to the 5' end of mRNAom was obtained from a partially purified preparation of mRNAom by polymerization by reverse transcriptase in the presence of a restriction fragment primer from pOM100. The complementary DNA mixture was amplified by molecular cloning using poly dG/dC tailing to form recombinant bacterial plasmids. Recombinant plasmids containing ovomucoid DNA sequences were selected by in situ hybridization to 32P-labeled pOM100 fragments. The longest plasmid containing ovomucoid DNA sequences was designated pOM502. The complete DNA sequence of both pOM100 and pOM502 was determined. The two plasmids appear to contain sequences complementary to the entire length of mRNAom. The nucleic acid sequence agrees with the known amino acid sequences for both ovomucoid and its N-terminal signal peptide. Highly homologous sequences occur in two regions that coincide with structural domains of the protein. Comparison of the sequence of mRNAom with that for other eucaryotic mRNAs allowed identification of possible functional regions in the mRNA molecule.

Animals↗