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Biomedical subjects

P Phan

Publications and source records attributed to P Phan.

7 recordsLinked to original sources
PubMed2001

Structural and functional characterization of second-coordination sphere mutants of soybean lipoxygenase-1.

Lipoxygenases are an important class of non-heme iron enzymes that catalyze the hydroperoxidation of unsaturated fatty acids. The details of the enzymatic mechanism of lipoxygenases are still not well understood. This study utilizes a combination of kinetic and structural probes to relate the lipoxygenase mechanism of action with structural modifications of the iron's second coordination sphere. The second coordination sphere consists of Gln(495) and Gln(697), which form a hydrogen bond network between the substrate cavity and the first coordination sphere (Asn(694)). In this investigation, we compared the kinetic and structural properties of four mutants (Q495E, Q495A, Q697N, and Q697E) with those of wild-type soybean lipoxygenase-1 and determined that changes in the second coordination sphere affected the enzymatic activity by hydrogen bond rearrangement and substrate positioning through interaction with Gln(495). The nature of the C-H bond cleavage event remained unchanged, which demonstrates that the mutations have not affected the mechanism of hydrogen atom tunneling. The unusual and dramatic inverse solvent isotope effect (SIE) observed for the Q697E mutant indicated that an Fe(III)-OH(-) is the active site base. A new transition state model for hydrogen atom abstraction is proposed.

Amino Acid Substitution↗
PubMed2000

Diagnostic odor recognition

Many diseases, toxic ingestions, and intoxications have characteristic odors. These odors may provide diagnostic clues that affect rapid treatment long before laboratory confirmation or clinical deterioration. Odor recognition skills, similar to auscultation and palpation skills, require teaching and practical exposure. Dr. Goldfrank and colleagues recognized the importance of teaching odor recognition to emergency service providers. They proposed the "sniffing bar" method for odor recognition training. OBJECTIVES: (1) To identify the recognition rates of medically important odors among emergency care providers. (2) To investigate the effectiveness of teaching odor recognition. Hypothesis: The recognition rates of medically important odors will increase after teaching exposure. METHODS: The study exposed emergency care providers to 11 tubes of odors. Identifications of each substance were recorded. After corrective feedback, subjects were re-tested on their ability to identify the odors. Analysis of odor recognition improvement after teaching was done via chi-square test. RESULTS: Improvement in identification after teaching was seen in all odors. However, the improvement was significant only in the lesscommon substances because their initial recognition was especially low. Significant changes may improve with a larger sample size. Subjects often confuse the odors of alcohol with acetone, and wintergreen with camphor. CONCLUSIONS: The recognition rates are higher for the more-common odors, and lower for the less-common odors. Teaching exposures to the less well-known odors are effective and can significantly improve the recognition rate of these substances. Because odor recognition may affect rapid diagnosis and treatment of certain medical emergencies such as toxic ingestion, future studies should investigate the correlation between odor recognition and the ability to identify corresponding medical emergencies.

Journal Article↗
PubMed1999

Validation of a controlled cortical impact model of head injury in mice.

A controlled cortical impact model of head injury was validated with mice. Mice were randomly assigned to moderate head injury, mild head injury, and sham injury groups. Beam balancing, open field activity, slant board inclination, grasp strength, and motor coordination were assessed prior to the injury and on days 1-5 postinjury. Morris water maze performance was evaluated on days 11-15 postinjury. Moderately head-injured mice took a significantly longer time to complete the motor coordination task and to find the hidden platform on the Morris water maze and had significantly fewer successful trials on both tasks than the mildly head-injured and sham-injured mice. Mildly head-injured and sham-injured mice performed similarly on both tasks. Contusion volume at the site of impact varied with severity of injury. Moderately head-injured mice had significantly larger contusions than mice with a mild head injury, and these mice in turn had significantly larger contusions than the sham-injured mice. Both moderately and mildly head injured mice had significantly fewer surviving cells in CA1 than the sham-injured mice but did not differ from each other in this regard. Although there was a group effect, only the mildly head-injured mice had significantly fewer surviving cells in CA3.

Animals↗
PubMed1996

Overexpression, purification, and generation of a thermostable variant of Zymomonas mobilis fructokinase.

The gene encoding fructokinase (EC 2.7.1.4) from Zymomonas mobilis has been expressed at high level in Escherichia coli by modifying the ribosome binding site using the polymerase chain reaction. A simple two-step purification from extracts of the recombinant cells results in highly purified enzyme suitable for use in fructose determination. Using the polymerase chain reaction in mutagenic conditions, a variant of fructokinase was isolated which was more thermostable than the wild type, taking the 30 min half-life from 70.1 to 72.4 degrees C. The purified thermostable variant had the same specific activity as the wild type. Sequencing of the variant indicated that only one amino acid was changed, with Ser 69 becoming Ala. Searches of the mutant libraries for variants that were (a) active with glucose or (b) had reduced inhibition by glucose were unsuccessful.

DNA Primers↗
PubMed1995

The physiological and anatomical demonstration of functionally selective parasympathetic ganglia located in discrete fat pads on the feline myocardium.

Experiments utilizing surgical parasympathectomy of discrete fat pad ganglia on the surface of the heart have suggested that there are two anatomically segregated and physiologically independent parasympathetic intracardiac ganglia which are capable of selective control of sino-atrial (SA) rate and atrio-ventricular (AV) conduction. Some pharmacological data, however, are inconsistent with these conclusions. We have examined the cardiodynamic effects of discrete injections of a ganglionic blocking drug into two fat pads on the surface of the cat heart. These fat pads were shown to contain ganglion cells histologically. It was observed that vagal effects upon cardiac rate are selectively mediated by neurons located in ganglia overlying the right pulmonary veins at the junction of the right atrium and superior vena cava. On the other hand, vagal effects upon AV conduction were selectively mediated by neurons located in a fat pad at the junction of the inferior vena cava and the inferior left atrium. These pharmacological data support the concept that specific intracardiac ganglia are capable of selective control of SA rate and AV conduction.

Adipose Tissue↗
PubMedDate not supplied

[Acute hepatic insufficiency disclosing congenital syphilis].

A breast-fed boy, born to first-cousin parents, had been vomiting since birth; his general condition remained good until age 6 weeks when vomiting became more frequent, and his status suddenly worsened, with polypnea, shock, hypothermia, jaundice, presence of blood in urine, gastric juice, stool, and bleeding tendency during veno-punctures. There was an huge hepatomegaly and a splenomegaly. Hypoglycaemia, metabolic acidosis, severe blood coagulation disturbances, elevated liver enzymes, hypoalbuminemia, pointed to an acute liver failure. He was resuscitated with current supportive measures, and was given a wide spectrum antibiotherapy. Because serologic tests for syphilis were positive in the child and his mother, including the presence of specific IgM the infant was then given Penicillin G therapy only, which resulted in a complete recovery. One month later, a needle liver biopsy showed residual signs of hepatitis. Other possible infectious or metabolic causes of acute liver failure occurring early in life had been excluded.

Acute Disease↗