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Diagnosis of burn depths is crucial to determine the treatment plan for severe burn patients. However, an objective method for burn depth assessment has yet to be established, although a commercial laser Doppler imaging (LDI) system is used limitedly. We previously proposed burn depth assessment based on photoacoustic imaging (PAI), in which thermoelastic waves originating from blood under the burned tissue are detected, and we showed the validity of the method by experiments using rat models with three different burn depths: superficial dermal burn, deep dermal burn and deep burn. On the basis of those results, we recently developed a real-time PAI system for clinical burn diagnosis. Before starting a clinical trial, however, there is a need to reveal more detailed diagnostic characteristics, such as linearity and error, of the PAI system as well as to compare its characteristics with those of an LDI system. In this study, we prepared rat models with burns induced at six different temperatures from 70 to 98 8C, which showed a linear dependence of injury depth on the temperature. Using these models, we examined correlations of signals obtained by PAI and LDI with histologically determined injury depths and burn induction temperatures at 48 hours postburn. We found that the burn depths indicated by PAI were highly correlative with histologically determined injury depths (depths of viable vessels) as well as with burn induction temperatures. Perfusion values measured by LDI were less correlative with these parameters, especially for burns induced at higher temperatures, being attributable to the limited detectable depth for light involving a Doppler shift in tissue. In addition, the measurement errors in PAI were smaller than those in LDI. On the basis of these results, we will be able to start clinical studies using the present PAI system.

The cyclic process of biosynthesis and degradation of poly(3-hydroxyalkanoate) (PHA) was studied in Alcaligenes eutrophus under conditions of nitrogen-limitation of growth. A. eutrophus cells, which had accumulated poly(3-hydroxybutyrate) (PHB) of 55 wt% content within cells from butyric acid, were transferred into a nitrogen-free medium containing pentanoic acid as the sole carbon source and cultivated at 30 degrees C and pH 7.5. The content of PHB in A. eutrophus cells decreased with time, whereas a copolyester of 3-hydroxybutyrate (HB) and 3-hydroxyvalerate (HV) units, P(HB-co-HV), was accumulated in the presence of pentanoic acid. Conversely, when A. eutrophus cells with 50 wt% content of P(HB-co-56% HV) were incubated in a nitrogen-free medium containing butyric acid, the content of P(HB-co-56% HV) decreased with time, whereas PHB was accumulated. These results indicate the cyclic nature of PHA metabolism in A. eutrophus under these conditions.

The cyclic process of biosynthesis and degradation of poly(3‐hydroxyalkanoate) (PHA) was studied in Alcaligenes eutrophus under conditions of nitrogen‐limitation of growth. A. eutrophus cells, which had accumulated poly(3‐ydroxybutyrate) (PHB) of 55 wt% content within cells from butyric acid, were transferred into a nitrogen‐free medium containing pentanoic acid as the sole carbon source and cultivated at 30°C and pH 7.5. The content of PHB in A. eutrophus cells decreased with time, whereas a copolyster of 3‐hydroxybutyrate (HB) and 3‐hydroxyvalerate (HV) units, P(HB‐co‐HV), was accumulated in the presence of pentanoic acid. Conversely, when A. eutrophus cells with 50 wt% content of P(HB‐co‐56% HV) were incubated in a nitrogen‐free medium containing butyric acid, the content of P(HB‐co‐56% HV) decreased with time, whereas PHB was accumulated. These results indicate the cyclic nature of PHA metabolism in A. eutrophus under these conditions.

1. Summary The structure of native poly(3‐hydroxybutyrate) (PHB) granules of Alcaligenes eutrophus was characterized in wet cells or wet granules by analysis of X‐ray diffraction. The PHB granules in intact cells were completely amorphous, but became crystalline after treatment with alkali or sodium hypochlorite. The native PHB granules were isolated from the cells by treatment with enzymes and sonic oscillation. The isolated PHB granules remained amorphous in suspension. The PHB granules were crystallized by various treatments with aqueous acetone, alkaline solution (of either NaOH or sodium hypochlorite), and lipase in an aqueous environment. These results suggest that crystallization of PHB molecules is started by the removal of a lipid component from native granules by various treatments.

The metabolic pathways of poly(3-hydroxybutyrate) (PHB) and polyphosphate in the microorganism Alcaligenes eutrophus H16 were studied by 'H, '3C, and 31P nuclear magnetic resonance (NMR) spectroscopy and by conventional analytical techniques. A. eutrophus cells accumulated two storage polymers of PHB and polyphosphate in the presence of carbon and phosphate sources under aerobic conditions after exhaustion of nitrogen sources. The solid-state cross-polarization/magic-angle spinning 13C NMR spectroscopy was used to study the biosynthetic pathways of PHB and other cellular biomass components from 13C-labeled acetate. The solid-state 13C NMR analysis of lyophilized intact cells grown on [1-_3C]acetate indicated that the carbonyl carbon of acetate was selectively incorporated both into the carbonyl and methine carbons of PHB and into the carbonyl carbons of proteins. The 31P NMR analysis of A. eutrophus cells in suspension showed that the synthesis of intracellular polyphosphate was closely related to the synthesis of PHB. The roles of PHB and polyphosphate in the cells were studied under conditions of carbon, phosphorus, and nitrogen source starvation. Under both aerobic and anaerobic conditions PHB was degraded, whereas little polyphosphate was degraded. The rate of PHB degradation under anaerobic conditions was faster than that under aerobic conditions. Under anaerobic conditions, acetate and 3-hydroxybutyrate were produced as the major extracellular metabolites. The implications of this observation are discussed in connection with the regulation of PHB and polyphosphate metabolism in A. eutrophus.

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