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D W Martin

Publications and source records attributed to D W Martin.

157 records · Page 9Linked to original sources
PubMed1970

The appearance and disappearance of the post-transcriptional repressor of tyrosine aminotransferase synthesis during the HTC cell cycle.

The synthesis of the enzyme tyrosine aminotransferase in HTC cells (an established line of rat hepatoma cells) is inducible by glucocorticoid hormones only during the latter part of G1 phase and throughout S phase in the cell generation cycle. We have earlier shown that during the first few hours of G1 phase when the enzyme cannot be induced, its synthesis is constitutive, presumably using as template, preexisting messenger RNA. Our model for tyrosine aminotransferase gene regulation in eukaryotic cells entails a specific post-transcriptional repressor which is formed only during the periods in the cell cycle when tyrosine aminotransferase is inducible. This model predicts that during the noninducible period, G2, the tyrosine aminotransferase repressor would not be present and thus tyrosine aminotransferase synthesis would be constitutive. Data are presented which confirm this prediction in further support of the model.

Animals↗
PubMed1969

Control of specific gene expression examined in synchronized mammalian cells.

The control of synthesis of the steroid-inducible enzyme, tyrosine aminotransferase (TAT), has been studied in synchronized cultures of HTC cells, an established line of rat hepatoma cells. During the mitotic and early G1 periods of the generation cycle of cells previously exposed to inducer, TAT synthesis is maximal in the absence of inducer, i.e., synthesis is constitutive. (By contrast, in random cells maximal TAT synthesis is always dependent upon the presence of the inducer.) After the third hour of G1 "G1[3]"), TAT synthesis is inhibited by a specific posttranscriptional repressor, the formation of which requires RNA synthesis. We speculate that this repressor is antagonized by the steroid inducer. The degradation of TAT during mitosis and G1 is constant and not affected by cycloheximide or actinomycin D in our experiments.

Animals↗
PubMed1966

Energetics of coupled active transport of sodium and chloride.

A Clark electrode was used to measure oxygen consumption by the gall bladder, in which there is a direct and one-to-one linkage between active Na and active Cl transport. O2 uptake was reversibly depressed when Cl in the mucosal bathing solution was replaced by a poorly transported anion, such as sulfate. This effect of Cl was abolished by ouabain or in Na-free solutions. When the anion was chloride, treatment with ouabain or replacement of Na by a poorly transported cation depressed QO2 more than did replacement of Cl. However, ouabain or removal of Na also depressed QO2 in Na2SO4 solutions, in which salt transport is minimal. It is concluded that oxygen uptake in the gall bladder consists of three fractions: 9% requires both Na and Cl, is inhibited by ouabain, and is linked to the NaCl pump; 36% requires Na but not Cl, is inhibited by ouabain, and possibly is linked to the cellular K uptake mechanism; and 55% represents basal uptake. If the extra oxygen uptake observed during transport supplies all the energy for transport, then 25 Na + 25 Cl ions are transported actively per O2 consumed; i.e., twice as many ions as in epithelia which transport only Na actively. This extra uptake is more than sufficient to supply the energy for overcoming internal membrane resistance under the experimental conditions used.

Animals↗
PubMedDate not supplied

Cloning of decay-accelerating factor suggests novel use of splicing to generate two proteins.

Decay-accelerating factor (DAF), a glycoprotein that is anchored to the cell membrane by phosphatidylinositol, binds activated complement fragments C3b and C4b, thereby inhibiting amplification of the complement cascade on host cell membranes. Here, we report the molecular cloning of human DAF from HeLa cells. Analysis of DAF complementary DNAs revealed two classes of DAF messenger RNA, one apparently derived from the other by a splicing event that causes a coding frameshift near the C terminus. The apparent 'intron' sequence contains an Alu family member and encodes contiguous protein sequence. Two DAF proteins are therefore possible, having divergent C-terminal domains which differ in their hydrophobicity. Both mRNAs are found on polysomes, suggesting that both are translated. We propose that the major (90%) spliced DAF mRNA encodes membrane-bound DAF whereas the minor (10%) unspliced DAF mRNA may encode secreted DAF and we present expression data supporting this. The deduced DAF sequence contains four repeating units homologous to a consensus repeat found in a recently described family of complement proteins.

CD55 Antigens↗
PubMedDate not supplied

Equilibrium constants for some steps of the reaction cycle of the sarcoplasmic reticulum calcium pump.

This paper summarizes true equilibrium measurements for some partial reactions of the sarcoplasmic reticulum calcium pump transport cycle. The most important result is the estimation of the equilibrium constant for the interconversion of the two major conformational states of the protein, E (Ca2+ binding sites facing the cytoplasm) and E' (Ca2+ binding sides facing the sarcoplasmic reticulum lumen). The value of K0 = [E']/[E] cannot be evaluated directly by any method available at present, but observed cooperativity in the binding of Mg2+ and Ca2+ to unliganded protein strongly indicates that K0 much greater than 1. The most probable value, valid within an order of magnitude, is K0 congruent to 10(3), i.e., the E' state is more stable than the E state by about 4 kcal/mol.

Animals↗