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Biomedical subjects

R Poon

Publications and source records attributed to R Poon.

At least 37 records · Page 2Linked to original sources
PubMed1988

A physician office analyzer. Evaluation of quality of results obtained by technical and nontechnical personnel.

We evaluated the Abbott Vision analyzer (Abbott Laboratories, North Chicago, Ill) both in a controlled laboratory setting and with several untrained individuals. We used control serum samples supplied by the manufacturer. Method comparison was performed with methods currently in use in our laboratory. The analytes evaluated were glucose, urea nitrogen, urate, cholesterol, triglycerides, and alkaline phosphatase. In the laboratory, the within-run precision (coefficient of variation) of all methods ranged from 0.8% to 3.4%; the range for between-run precision was 1.2% to 3.3%. Correlation between the Abbott Vision analyzer and routine methods was excellent. The upper limit of linearity for all methods was as stated by the manufacturer. The coefficient of variation obtained by ten nontechnical personnel ranged from 0.0% to 3.9%. The correlation between results obtained by the nontechnologist were excellent. Our study indicates the Abbott Vision analyzer is extremely easy to operate and provides reliable results in the hands of nontechnical personnel.

Allied Health Personnel↗
PubMed1988

Physician office analyzers. Do they satisfy medically useful criteria for analytical performance of laboratory tests?

The coefficients of variation (CVs) for several tests on physician office analyzers were compared with published data for medically useful criteria of these tests. Medically useful CVs were based on physicians' opinions of significant changes in laboratory tests. Precision studies using control material were carried out on four physician office analyzers by both a trained technologist and nontechnical personnel, such as physicians, nurses, and medical office personnel. This study was carried out during a six-month period. The instruments that were evaluated were the Reflotron, Seralyzer, Vision, and DT60. Low and high concentrations of quality control material, supplied by the manufacturer and those in use in the study laboratory (Omega I and II, Cooper Biomedical, Fairhaven, NJ), were used. With few exceptions, all instruments satisfied the medically useful CVs criteria, ie, the precision obtained by both the technologist and nontechnical personnel either equaled or exceeded the precision requirements set by physicians.

Autoanalysis↗
PubMed1987

Interference by cephalosporins with creatinine measurement by desk-top analyzers.

We have carried out a study to evaluate the interference by cephalosporins with the measurement of creatinine by desk-top analyzers. The cephalosporins evaluated at concentrations of 0-250 mg/l were cefazolin sodium, cefoxitin sodium, cefotaxime sodium, and ceftazidime pentahydrate. The instruments evaluated were DT60 (Kodak, Rochester, USA), Seralyzer (Ames Division, Miles Laboratories, IN, USA), and Vision (Abbott Labs, Chicago, USA). All studies were done in plasma. None of the cephalosporins showed any interference with the DT60 analyzer. With the Vision and Seralyzer no interference was seen with cefotaxime or cefazolin. With cefazolin an increase of 10-20 mumol/l creatinine was seen for every 20 mg/l of drug; with cefoxitin there was an increase of 50-80 mumol/l of creatinine for every 100 mg/l of drug. Erroneous creatinine values may be found in patients taking cefazolin and cefoxitin and may lead to inappropriate clinical management.

Cefazolin↗
PubMed1985

Indican interference with six commercial procedures for measuring total bilirubin.

We have studied the effect of indican on six commercial procedures for the measurement of total bilirubin in serum. Total bilirubin measured by the Bilirubin A-Gent (Abbott) 2,4-dichlorophenyl diazonium procedure increased by 50 mg/L for each 1 mmol/L of added indican. Similarly, total bilirubin measured by the Bilirubin C-System (Boehringer Mannheim) 2,5-dichlorophenyl diazonium procedure increased by 33 mg/L per mmol/L of indican. Indican also interfered with the Micro Bilirubin Reagent Set (Harleco) Malloy-Evelyn procedure, but to a much lesser extent. The Jendrassik Bilirubin Reagent System (American Monitor) and a modified Jendrassik-Grof procedure (Hoffmann-LaRoche) adapted to the Cobas Bio analyzer were unaffected by the presence of indican. The amount of interference with the 2,5-dichlorophenyl diazonium procedure increased significantly with color development time and was twice the initial amount after 30 min. Concentrations of indican as high as 0.38 mmol/L have been found in sera of patients with renal failure, which would increase total bilirubin values measured by the first two procedures above by 19 and 12 mg/L, respectively. Users of these procedures should therefore be suspicious of unexpectedly high bilirubin values obtained with sera from patients with chronic renal disease.

Autoanalysis↗
PubMed1978

The nucleotide sequence of the 5' untranslated region of human gamma-globin mRNA.

The nucleotide sequence of the entire 5' untranslated region of human gamma-globin mRNA has been determined. This was accomplished by analyzing complementary DNA (cRNA) synthesized from the mRNA with reverse transcriptase. The CDNA was labeled at its 3' end with 32"p using terminal deoxynucleotidyl transferase, digested with the restriction endonuclease Hae III and the end-labeled fragment isolated ans sequenced by the method of Maxam and Gilbert. Including the initiation codon AUG, the 5' untranslated region of human gamma-globin mRNA contains 57 nucleotides, compared to 41 in alpha- and 54 in beta-globin mRNA. There is very little homology between alpha and gamma sequences in the 5' region. There is considerable homology between beta- and gamma-globin mRNAs in the regions proximal and distal to the initiation codon, but the entire sequence shows less homology than the human and rabbit beta-globin mRNAs. The hexanucleotide sequence CUUCUG is found near the 5' ends of all three human globin mRNAs, suggesting a possible role of this sequence or ribosomal binding. Both guanosine and cytidine were found at the 19th nucleotide position from the 5' end of the gamma mRNA. We believe this heterogeneity arises from the difference in nucleotide sequence between the A gamma and G gamma loci.

Base Sequence↗
PubMed1978

Sequence of the 3'-noncoding and adjacent coding regions of human gamma-globin mRNA.

In cloning human fetal globin cDNA in bacterial plasmids, we obtained a recombinant which contained a fragment of gammg-globin cDNA corresponding to the region from amino acid 99 to the poly A. We determined a sequence of 169 nucleotides which included the complete 3' non-coding region of the gamma-globin mRNA. The codon for amino acid 136 was GCA, indicating that this cloned fragment was derived from the Agamma-globin gene. In conjunction with the surrounding sequences, the GCA codon provides the Agamma-species with a unique CTGCAG hexanucleotide that is recognized by the restriction enzyme Pst I. The 3'-untranslated region of the gamma-globin mRNA consists of 90 nucleotides, and shares little homology with that of the human beta-globin mRNA. As in other mammalian mRNAs, a symmetrical sequence and the hexanucleotide AAUAAA are present.

Base Sequence↗
PubMed1977

Rabbit globin mRNA: analysis of T1 RNAse digestion fragments.

Rabbit globin complementary DNA made with RNA-dependent DNA polymerase (reverse transcriptase) was used as a template for in vitro synthesis of 32P-labeled RNA and deoxysubstituted RNA. The sequences of the nucleotides in most of the fragments resulting from combined ribonuclease T1 and alkaline phosphatase digestion have been determined. In addition, the 3' nearest neighbor was determined for several fragments resulting from digestion with T1 ribonuclease. The utility of the deoxysubstitution technique was demonstrated by the ease with which the sequences of pyrimidine-rich fragments could be determined. Many sequences thus determined were long enough to fit uniquely with the alpha- or beta-globin amino acid sequences. The positions of these fits were found to be clustered, leading us to believe that only certain regions of the complementary DNA are transcribed by Escherichia coli RNA polymerase. Other unique characteristics of RNA synthesis from a complementary DNA template include a high yield of free poly(A) and the fact that one must use low rather than high salt buffers to obtain transcripts of high molecular weight.

Amino Acid Sequence↗
PubMed1977

Single-strand nicking of DNA in vitro by neocarzinostatin and its possible relationship to the mechanism of drug action.

Neocarzinostatin, a protein antibiotic with anti-tumor activity was found to place single-strand scissions in DNA in an in vitro reaction. The drug's cutting activity was strongly dependent on the presence of 2-mercaptoethanol or dithiothreitol but some cutting did take place in the absence of reducing agent at very high drug levels and prolonged incubation. The requirement for reducing agents could not be replaced with NAD+, FAD, NADH or H2O2 and the strand-scission reaction was not affected by Mg2+, EDTA or intercalating agents. Similar profiles of heat-inactivation of neocarzinostatin were found whether activity was measured by the scission of DNA strand either in vitro or in HeLa cells treated with the drug. Furthermore, both of these parameters corresponded closely with the ability of the modified drug to inhibit DNA synthesis and growth of HeLa cells. By column isoelectric focusing it was shown that all four activities are associated with the same protein band (pH 3.28). From these data we conclude that the cytotoxic activity of neocarzinostatin and the nicking of DNA strands in vitro appear to reside in the same protein.

Antibiotics, Antineoplastic↗
PubMed1977

Characterization of DNA strand breakage in vitro by the antitumor protein neocarzinostatin.

The antitumor protein antibiotic neocarzinostatin causes strand scission of DNA in vitro in the presence of a sulfhydryl compound. The breaks are single stranded in nature and bear 5'-phosphoryl termini. All four deoxymononucleotides are recoverable at the 5'-ends of the cleavage sites although a higher proportion of dGMP and TMP are consistently found. The lesions are not repairable with polynucleotide ligase from Escherichia coli. A quantitative assay was developed to determine the pH profile and time course of the reaction. Data from protection experiments with synthetic and natural DNAs indicate the requirement for thymidylic acid and deoxyadenylic acid in the DNA for cutting. In DNA-RNA hybrids, riboadenylic acid can substitute for deoxyadenylic acid, whereas ribouridylic acid cannot substitute for thymidylic acid. Release of thymine is detected, and the amount of release correlates well with the number of strand scissions.

Antibiotics, Antineoplastic↗
PubMed1977

The nucleotide sequences of the untranslated 5' regions of human alpha- and beta-globin mRNAs.

The complete sequences of the untranslated 5' regions of human alpha- and beta-globin mRNAs were determined by sequence analysis of full-length cDNAs. The single-stranded cDNAs were digested with the restriction endonuclease Hae III, and the two 3'-terminal fragments of 75 and 132 nucleotides, complementary to the 5' termini of the alpha- and beta-globin mRNAs, respectively, were isolated and sequenced. Including the initiation codon AUG, the untranslated 5' regions of human alpha- and beta-globin mRNAs contain 41 and 54 nucleotides, respectively, and exhibit striking homologies with the corresponding sequences in the rabbit. Human alpha- and beta-globin mRNAs have five bases in the region of the initiation codon that may form base pairs with the 3' terminus of 18S rRNA. Stable secondary structures with hairpin loops can be constructed in the untranslated 5' regions.

Base Sequence↗