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Biomedical subjects

L Goldstein

Publications and source records attributed to L Goldstein.

At least 217 records · Page 12Linked to original sources
PubMed1977

Small nuclear RNA localization during mitosis. An electron microscope study.

The localization of small nuclear ribonucleic acids (snRNAs) during mitosis in Amoeba proteus was studied by high voltage (1,000 kV) electron microscope autoradiography. By suitable micromanipulations, the snRNA's, labeled with [3H]uridine, were made to be the only radioactive molecules in the cell and thus easy to follow autoradiographically. During interphase the snRNA label, which is almost exclusively nuclear, is distributed fairly uniformly through the nucleus with a slightly higher amount of label over chromatin than over nonchromatin areas. During prophase the snRNAs, which continue to be largely nuclear, become highly concentrated in the condensing chromosomes. At metapase, almost all of the snRNAs are cytoplasmic and essentially none are associated with the maximally condensed chromatin. Beginning in early anaphase, the snRNAs resume their association with the chromosomes, with the degree of association increasing throughout anaphase. Most of the snRNAs are back in the nuclei by telophase, but the intranuclear localization is hard to determine. We conclude that snRNAs have a great affinity for the partially condensed chromosomes of prophase and anaphase, but none for the maximally condensed chromosomes of metaphase. A minor amount of snRNA localizations in association with nucleoli and the nuclear envelope are also reported. On the basis of these findings a role of snRNAs in genetic "reprogramming" or chromosome organization is proposed.

Amoeba↗
PubMed1976

The formation of alanine from amino acids in diaphragm muscle of the rat.

Alanine production and pyruvate content of the isolated rat hemidiaphragm are increased by isoleucine or glutamate. These results support the hypothesis that amino acids are converted into pyruvate before oxidation and that some pyruvate is transaminated to alanine, which is released from the muscle.

Alanine↗
PubMed1976

Electroencephalographic laterality changes during human sexual orgasm.

Left and right parietal EEGs were recorded while seven subjects experienced sexual climax through self-stimulation. EEG data were quantified by continuous cumulated measurements of the integrated areas of EEG recording during successive 1-sec epochs. In eight out of 12 experiments, this measure revealed a statistically significant change in laterality. Controlled replications with two of the original subjects obviated the possibility that two potential sources of artifact (hand used for masturbation and gross body movements) accounted for the changes. While previous research has focused on vasomotor and myotonic indices of sexual response, this study demonstrates the significance of brain phenomena in sexual orgasm.

Adult↗
PubMed1976

Salmonella typhimurium SA host specificity system is based on deoxyribonucleic acid-adenine methylation.

We have determined the nature of the deoxyribonucleic acid (DNA) modification governed by the SA host specificity system of Salmonella typhimurium. Two lines of evidence indicate that SA modification is based on methylation of DNA-adenine residues. (i) The SA+ locus of Salmonella was transferred into Escherichia coli B, a strain that does not contain 5-methylcytosine in its DNA; although the hybrid strain was able to confer SA modification, its DNA still did not contain 5-methylcytosine. (ii) the N6-methyladenine content of phage L DNA was measured after growth in various host strains; phage lacking SA modification contained fewer N6-methyladenine residues per DNA. We also investigated the possibility, suggested by others (32), that SA modification protects phage DNA against restriction by the RII host specificity system. Phages lambda, P3, and L were grown in various SA+ and SA- hosts and tested for their relative plating ability on strains containing or lacking RII restriction; the presence or absence of SA modification had no effect on RII restriation. In vitro studies revealed, however, that Salmonella DNA is protected against cleavage by purified RII restriction endonuclease (R-EcoRII). This protection is not dependent on SA modification; rather, it appears to be due to methylation by a DNA-cytosine methylase which has overlapping specificity with the RII modification enzyme, but which is not involved in any other known host specificity system.

Adenine↗
PubMed1976

Intracellular osmoregulatory role of amino acids and urea in marine elasmobranchs.

Little skates, Raja erinacea, and stingrays, Dasyatis americana, were gradually transferred over a period of 4-5 days from full strength to approximatley 50% seawater. Plasma and muscle osmolarity fell. Hematocrits were essentially unchanged. Extracellular fluid volume (ECF) of muscle, estimated as the chloride space, increased 70% during this period. Regulation of muscle cell volume was associated with sharp declines in cellular concentrations of total amino acids (ninhydrin-positive materials) and urea. The osmoregulatory importance of the free amino acid pool in erythrocytes and muscle was a particularly prominent feature in both species. Intracellular amino acid concentration in R. erinacea muscle fell from 214 to 144 mmol/liter during transfer to 50% seawater, urea from 398 to 264, and trimethylamine oxide (TMAO) dropped from 63.9 to 35.8 mmol/liter. TMAO plasma levels were similar in stingray and skate, but muscle TMAO concentrations were much higher in the former. Urea content in stingray plasma greatly exceeded that in R. erinacea-630 and 574 mmol/liter in two specimens-perhaps the highest recorded.

Amino Acids↗
PubMed1975

The fate and origin of the nuclear envelope during and after mitosis in Amoeba proteus. I. Synthesis and behavior of phospholipids of the nuclear envelope during the cell life cycle.

The synthesis and behavior of Amoeba proteus nuclear envelope (NE) phospholipids were studied. Most NE phospholipid synthesis occurs during G2 and little during mitosis or S. (A. proteus has no G1 phase). Autoradiographic observations after implantation of [3-H] choline nuclei into unlabeled cells reveal little turnover of NE phospholipid during interphase but during mitosis all the label is dispersed through the cytoplasm. Beginning at telophase all the label is dispersed through the cytoplasm. Beginning at telophase all the NE phospholipid label returns to the daughter NEs. This observation, along with the finding that no NE phospholipid synthesis occurs during mitosis or S, indicates that no de novo NE phospholipid production is required for newly forming NEs. Similarlyemetine, at concentrations that inhibit 97 percent of protein synthesis, does not prevent the post mitotic formation of NEs, suggesting that previously manufactured proteins are used in making new NEs. If a nucleus containing labeled NE phospholipids is transplanted into an unlabeled nucleate cell and the cell is allowed to grow and divide, the resultant four nuclei are equally labeled. This finding supports, but does not prove (see next paragraph), the conclusion that there probably is no continuity of the A. proteus NE during mitosis. When a phospholipid-labeled nucleus is implanted into a cell in mitosis, the grafted nucleus is not induced to enter mitosis. There is, however, a marked increase in the turnover of that nucleus's NE phospholipids with no apparent breakdown of the NE; this indicated that the mitotic cytoplasm possesses a factor that stimulates NE phospholipid exchange with the cytoplasm. That enhanced turnover is not accompanied by visible structural alteration makes less certain the earlier conclusion that no NE continuity exists during mitosis. Perhaps the most important finding in this study is that there are present, at restricted times in the cell cycle, factors capable of inducing accelerated exchange of structural components without microscopically detectable disruptions of structure.

Amoeba↗
PubMed1975

Renal glutaminase adaptation and ammonia excretion in infant rats.

The purpose of this investigation was to determine the role of enzyme adaptation in the response of ammonia excretion to acidosis in developing rats. The response of renal ammonia excretion was low in infant rats (7-12 days old) following administration of a single dose of acidifying salt (5 mmol NH4CL/kg). However, repeated administration (2 times daily) of the salt increased ammonia excretion two- to threefold within 2 days. This adaptive response was associated with a concomitant rise in renal phosphate-dependent glutaminase (PDG) activity; PDG activity increased from approximately 36% adult level in untreated infants to 79% adult level in infants given NH4Cl for 2 days. Ammonia excretion and PDG activity decreased in parallel following cessation of NH4Cl treatment. Administration of the antibiotic, actinomycin D (100 mug/kg, ip, 2 times daily for 2 days) completely inhibited the response of PDG to repeated NH4Cl administration. In contrast to the situation previously observed in adult rats, actinomycin D treatment prevented the acid-induced rise in renal ammonia excretion. These results suggest that the level of renal PDG plays a more direct role in the adaptation of ammonia excretion to acidosis in infant rats than in adults.

Acid-Base Equilibrium↗