Kivie Moldave

Studies on conversion of phenylalanine to tyrosine in phenylpyruvic oligophrenia.

Summary A homogenate of a biopsy specimen of liver obtained from a patient with phenylpyruvic oligophrenia did not catalyze detectable conversion of phenylalanine to tyrosine, under conditions whereby liver homogenates obtained from normal individuals were active in catalyzing such conversion. Addition of a fraction prepared from rat liver (which exhibited relatively low activity alone) to the inactive phenylketonuric liver homogenate resulted in striking activation of the conversion of phenylalanine to tyrosine.

Effect of ribosomes on the biosynthesis of ribonucleic acid in vitro

Abstract A deoxyribonucleoprotein that contains RNA polymerase activity and DNA template has been isolated from Escherichia coli and partially purified by zone sedimentation. This preparation synthesizes RNA in the presence of all four nucleoside triphosphates and in the absence of exogenous DNA; the nascent RNA remains attached to the enzyme—template complex during the polymerization reaction. The addition of ribosomes stimulates the synthesis of RNA; the RNA made in the presence of ribosomes is of higher molecular weight than that made in their absence and a significant portion of the nascent RNA is released from the enzyme—template complex, in the form of RNA-ribosome aggregates. Evidence has been obtained that ribosomes, natural acceptors for the nascent RNA, exert a direct effect on RNA synthesis as a consequence of attachment to the growing chain, and possibly of ribosome movement, but not of protein synthesis-dependent movement of the ribosome along the RNA chain.

Characterization of the ribonucleic acid synthesized during amino acid-deprivation of a stringent auxotroph of Escherichia coli

Abstract A polyauxotrophic stringent mutant of Escherichia coli was used to study the nature of the RNA synthesized during amino acid starvation. A small amount of RNA, about 5% of that observed in exponentially growing cells, is made when essential amino acids have been withdrawn from the culture medium. This RNA resembles pulse-labeled messenger RNA of exponentially growing cells in zone sedimentation pattern, size distribution, localization in polysomes, base composition and decay characteristics in the presence of actinomycin. When RNA-labeled cells, from amino acid-deprived or amino acid-supplemented cultures, are incubated in complete media with actinomycin, a biphasic decay curve is obtained; the initial half-life is three to four minutes, and about 25% of the RNA is resistant to decay in both types of cell. Incubation with actinomycin leads to the conversion of considerable quantities of polysomeassociated RNA to acid-soluble products. The residual fraction of RNA resistant to decay in the presence of actinomycin can be detected in the 70 s ribosome region, reveals distinct peaks of 23, 16 and 4 s RNA on sucrose gradients, and has a base composition resembling that of ribosomal RNA. All classes of RNA examined, such as messenger and small amounts of stable RNAs, appear to be made in amino acid-deprived cells; however, the high relative proportion of messenger RNA is not consistent with proposals that require a common, co-ordinate regulation of the synthesis of all cellular RNAs.

The effect of vitamin B6 on the in vivo utilization of radioactive phenylalanine.

Abstract The in vivo incorporation of phenylalanine-C 14 into tissues of control and vitamin B 6 -deficient rats was investigated. Thirty minutes after the administration of the isotope, markedly higher levels of C 14 were found in the acid-soluble, lipide, and protein fractions of all control tissues examined as compared to those of vitamin B 6 -deficient rats. Two hours and 7 hr. after the administration of phenylalanine-C 14 , the acid-soluble fraction of all tissues from vitamin B 6 -deficient animals exhibited higher levels of radioactivity than did similar tissues from control animals; however, the radiocarbon concentration in the lipides and proteins of control tissues remained higher. The administration of 1 mg. of pyridoxal daily for 3 days prior to the injection of phenylalanine-C 14 affected only slightly the uptake of C 14 in control animals; the levels of radioactivity in tissues from deficient animals similarly treated with pyridoxine tended to approximate control levels. The relation of these findings to amino acid transport into cells and to protein metabolism is discussed.

Utilization of Labeled Proteins in Synthesis of Tissue Proteins.

Summary Ehrlich ascites cells were incubated in vitro with radioactive amino acids or radioactive ascites proteins prepared biosynthetically. Incubations with free amino acids resulted in accumulation of large amounts of radioactivity in the acid-soluble fraction and in incorporation of radioactivity into the proteins. Incubations with labeled proteins resulted in labeling of cell proteins without significant accumulation of radioactivity in the acid-soluble fraction. Radioactive proteins were isolated from various cell fractions of ascites cells following incubation with labeled free amino acids or proteins. These results suggest that proteins enter ascites cells where they are utilized for synthesis of cellular proteins; free amino acids do not appear to be intermediates in this process.

In vivo release of radiocarbon from labeled Ehrlich's ascites carcinoma cells.

Summary Ascites cells labeled with radiocarbon from leucine-2-C14 were injected into mice. The amounts of radioactivity remaining in the acid-soluble, lipides, proteins and nucleic acids of the transplants for periods up to 5 days was measured. A marked loss of C14 from all of these components occurred within the first day but did not appear to be due to a reaction of the host against the inoculated cells. Between the 2nd and the 5th day a small but significant amount of the C14in the proteins and nucleic acids was lost per day. These results suggest that the transfer of labeled nitrogenous constituents from the tumor to the host tissues occurs to some extent. The possibility that these results may be due to the destruction of the cells must also be considered.