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Biomedical subjects

J Baldwin

Publications and source records attributed to J Baldwin.

108 records · Page 6Linked to original sources
PubMed1970

Functional significance of isoenzymes in thermal acclimatization. Acetylcholinesterase from trout brain.

1. The effects of acclimatization temperature on the catalytic properties of acetylcholinesterase from rainbow-trout brain were examined. 2. Trout brain acetylcholinesterase occurs in two distinct forms. A single ;warm' variant of the enzyme is present after acclimatization to 17 degrees C; a single ;cold' variant appears after acclimatization to 2 degrees C. Both forms are present in fish after acclimatization to an intermediate temperature. 3. The K(m) values of the enzyme variants for acetylcholine are temperature-dependent, the lowest values coinciding with the acclimatization temperature at which each enzyme was induced. 4. It is concluded that the K(m)-temperature relationship is adaptive, and that the critical process during thermal acclimatization, in cases where enzymes show sharp changes in K(m) with temperature, is the synthesis of a new enzyme variant that is better suited for catalysis and control of catalysis under the conditions of the acclimatized state.

Acetylcholinesterase↗
PubMedDate not supplied

Partitioning of respiration between the gills and air-breathing organ in response to aquatic hypoxia and exercise in the pacific tarpon, Megalops cyprinoides.

The evolution of air-breathing organs (ABOs) is associated not only with hypoxic environments but also with activity. This investigation examines the effects of hypoxia and exercise on the partitioning of aquatic and aerial oxygen uptake in the Pacific tarpon. The two-species cosmopolitan genus Megalops is unique among teleosts in using swim bladder ABOs in the pelagic marine environment. Small fish (58-620 g) were swum at two sustainable speeds in a circulating flume respirometer in which dissolved oxygen was controlled. For fish swimming at 0.11 m s(-1) in normoxia (Po2 = 21 kPa), there was practically no air breathing, and gill oxygen uptake was 1.53 mL kg(-0.67) min(-1). Air breathing occurred at 0.5 breaths min(-1) in hypoxia (8 kPa) at this speed, when the gills and ABOs accounted for 0.71 and 0.57 mL kg(-0.67) min(-1), respectively. At 0.22 m s(-1) in normoxia, breathing occurred at 0.1 breaths min(-1), and gill and ABO oxygen uptake were 2.08 and 0.08 mL kg(-0.67) min(-1), respectively. In hypoxia and 0.22 m s(-1), breathing increased to 0.6 breaths min(-1), and gill and ABO oxygen uptake were 1.39 and 1.28 mL kg(-0.67) min(-1), respectively. Aquatic hypoxia was therefore the primary stimulus for air breathing under the limited conditions of this study, but exercise augmented oxygen uptake by the ABOs, particularly in hypoxic water.

Air Sacs↗
PubMedDate not supplied

Substance misuse and HIV/AIDS risks among delinquents: a prevention challenge.

In the United States, there is growing concern that adolescents are at increasing risk for HIV-1 infection due to recreational substance use and sexual activity. Self-report questionnaires from a sample of 224 incarcerated delinquents quantified associations between drug use, sex, and other behaviors which risk HIV-1 infection. High rates of substance use and HIV-risking behaviors were found. Significant correlations between levels of substance use and both behavioral and attitudinal barriers to HIV/AIDS prevention programming were observed. This evidence and other subgroup differences in denial of vulnerability and in practice of preventive behaviors indicate the need for different approaches to prevention. An integrated HIV/AIDS and substance misuse prevention program is discussed as a viable alternative to the usual knowledge-enhancing programs.

Acquired Immunodeficiency Syndrome↗