Polypeptide involved in the Escherichia coli plasmid-mediated citrate transport system.

A genetic determinant conferring on Escherichia coli the ability to utilize citrate as a sole source of carbon and energy was subcloned into pBR322 from a naturally occurring, citrate utilization (Cit+) plasmid, pOH30221, and was localized to a 1.6-kilobase region by cloning and subsequent deletion analysis. Genetic expression of the Cit+ determinant in E. coli minicells revealed that the Cit+ determinant encoded a single, membrane-associated polypeptide with an apparent molecular weight of 35,000, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This polypeptide seemed not to be synthesized as a precursor with an amino-terminal signal sequence.     

Substrate specificities of active transport systems for amino acids in vacuolar-membrane vesicles of Saccharomyces cerevisiae. Evidence of seven independent proton/amino acid antiport systems

The substrate specificities of the amino acid transport systems of vacuoles of the yeast, Saccharomyces cerevisiae, were investigated using purified vacuolar-membrane vesicles (Ohsumi, Y., and Anraku, Y. (1981) J. Biol. Chem. 256, 2079-2082). Ten amino acids: arginine, lysine, histidine, phenylalanine, tryptophan, tyrosine, glutamine, asparagine, isoleucine, and leucine, were taken up actively into the vesicles. Kinetic studies indicated the presence of seven independent H+/amino acid antiport systems with narrow substrate specificity, which were all driven by a proton motive force established by ATP hydrolysis. The Kt and Vmax values, and the specific inhibitors for the arginine, arginine-lysine, histidine, phenylalanine-tryptophan, tyrosine, glutamine-asparagine, and isoleucine-leucine transport systems were determined.     

Highly potent and specific inhibitors of human renin

We designed aldehyde derivatives of small peptides representing the C-terminal portion of angiotensin I sequence as an inhibitor of human renin. Among compounds that we synthesized, benzyloxycarbonyl (Z)-Phe-His-Leucinal (compound V), Z-Pro-Phe-His-Leucinal (Compound IV) and Z-[3-(1'-naphthyl)Ala]-His-Leucinal (compound VII) markedly inhibited human renin (IC50, 7.5 X 10(-7), 3.2 X 10(-7) and 8.0 X 10(-8) mol/l, respectively). Compound VII was shown to be noncompetitive (Ki = 2.4 X 10(-7) mol/l). It did not inhibit either cathepsin D or pepsin. Compound V had slight or no inhibitory effect at the concentration of 10(-5) mol/l on six animal renins except for monkey and rabbit renins. Results obtained show that these aldehyde compounds are highly selective and species specific inhibitors for human and monkey renins.     

Changes of aldolase A and B messenger RNA levels in rat liver during azo-dye-induced hepatocarcinogenesis

The expression of aldolase A and B mRNAs during azo-dye-induced carcinogenesis in rat liver was examined. After feeding the dye for 18 weeks, the level of aldolase A mRNA increased to about 11 times that in a normal liver, with the concomitant decrease of aldolase B mRNA level to about 25% of that in a normal liver. These changes did not occur progressively during the carcinogenesis, but occurred as an additional phase after 4 week-feeding of the azo-dye. At this stage, the levels of aldolase A and B mRNAs were about 7 times and 45% of that in a normal liver, respectively. This biphasic pattern in the aldolase isozyme expression in the azo-dye-fed rat liver is discussed together with the kinetic data of the enzyme activity.     

Pharmacokinetic study of exogenously administered ß-endorphin using a rapid radioreceptor assay in rats

A rapid radioreceptor assay for measuring ß-endorphin (ß-EP) in unextracted serum has been developed. The method is based upon the inhibition by ß-EP of ³H-naloxone binding to the specific receptors on rat brain membranes, prepared in a stable form of pellets. Effect of serum on the assay was minimized by adding pooled serum to the equal dilution of total serum in the assay mixture. Pharmacokinetic analysis of pharmacologically active ß-EP equivalents (ß-EP eq.) in rats was performed using this method. The serum disappearance of ß-EP eq. after iv administration followed a biexponential decline and pharmacokinetic parameters were calculated by a two-compartment open model. The half-lives of α-phase and ß-phase were 2.6 ± 0.5 min and 6.2 ± 1.6 hr (mean ± SE; n=6), respectively. The volume of the central compartment (V₁) and that of steady-state (Vd_ss) were 67 ± 16 and 480 ± 75 ml/kg (mean ± SE; n=6), respectively. The total body serum clearance (CL_tot) was 2.1 ± 0.9 ml/min/kg (mean ± SE; n=6). The serum disappearance curve of ß-EP eq. obtained in the present study was similar to that previously reported by Houghten et al. (Proc. Natl. Acad. Sci. U.S.A. $\text{77}$, 4588–4591 (1980)), in which the disapperance of total radioactivity of tritiated ß-EP in rats was examined.     

28,000-dalton polypeptide (p28) of adult T-cell leukemia-associated antigen encoded by 24 S mRNA of human T-cell leukemia virus has an associated protein kinase activity

Human T-cell leukemia virus producer cell line MT-2 was labeled with [32P]phosphoric acid, and its cell extracts were immunoprecipitated with mouse monoclonal antibodies (GIN-7, and KK-1) and rabbit sera (anti-p24, and anti-gp68). Analysis of the immunocomplexes on sodium dodecyl sulfate-polyacrylamide gell electrophoresis revealed that p53, p28, and p19 of adult T-cell leukemia-associated antigens were phosphorylated in vivo. Immunocomplexes of MT-2 cell extract with monoclonal antibody KK-1 were incubated with [gamma-32P]ATP in vitro and it was revealed that the phosphokinase activity was associated with p28. The phosphokinase activity of p28 was specific to the serine residue but was not to the tyrosine residue.     

Video microscopy of colloidal gold particles and immuno-gold labelled microtubules in improved rectified DIC and epi-illumination

Modification of rectified Nomarski differential interference contrast optics (Nikon) and the epi-illumination system (Nikon IGS-cube) improved the detection of colloidal gold particles with analog video enhanced microscopy. Immuno-gold labelled microtubules of Haemanthus endosperm are visualized at a level of detection unmatched in conventional light microscopy. Single gold, or gold silver enhanced particles in suspension viewed with the modified epi-illumination after pressure injection into cells, are well distinguished from other granular cell components. Immuno-gold has also been detected on the surface of chromosomes and the nuclear envelopes in cells during the rapid experimental disassembly of microtubules. Thus, under certain conditions tubulin in a form other than microtubules may be detected. Practical applications of this "optical stain" for non fading immuno-gold 5-40 nm markers are discussed.