Studies on ferrochelatase. The enzymic formation of haem in proplastids, chloroplasts and plant mitochondria

1. Ferrochelatase was demonstrated in the chloroplasts and proplastids isolated from the primary leaves of beans (a dicotyledon) and oats (a monocotyledon). It was also detected in chloroplasts from etiolated bean seedlings made green by illumination before being harvested. The specific activities of the three types of bean organelles are similar, as are the specific activities of the oat proplastids and chloroplasts. 2. Chloroplasts from young spinach leaves also contain ferrochelatase; these chloroplasts were tested for their ability to form magnesium tetrapyrroles and found unable to catalyse the insertion of Mg(2+) into mesoporphyrin IX. 3. Ferrochelatase was also detected in potato tuber mitochondria. 4. Ferrochelatase activity in these plant preparations is much less stable on storage than similar preparations from bacteria and animal tissues. 5. Temperature affects the activities of spinach chloroplast ferrochelatase and rat liver ferrochelatase differently. Activity of the chloroplast enzyme increases as the temperature rises from 20.6 degrees to 26 degrees , but becomes increasingly inactivated as the temperature rises further to 38 degrees . The initial velocity of the mammalian enzyme, however, increases as the temperature rises from 25.8 degrees to 65 degrees , but the enzyme is inactivated after several minutes at 65 degrees .     

Pulmonary gas exchange in panting dogs

Pulmonary gas exchange during panting was studied in seven conscious dogs (32 kg mean body wt) provided with a chronic tracheostomy and an exteriorized carotid artery loop. The animals were acutely exposed to moderately elevated ambient temperature (27.5 degrees C, 65% relative humidity) for 2 h. O2 and CO2 in the tracheostomy tube were continuously monitored by mass spectrometry using a special sample-hold phase-locked sampling technique. PO2 and PCO2 were determined in blood samples obtained from the carotid artery. During the exposure to heat, central body temperature remained unchanged (38.6 +/- 0.6 degrees C) while all animals rapidly switched to steady shallow panting at frequencies close to the resonant frequency of the respiratory system. During panting, the following values were measured (means +/- SD): breathing frequency, 313 +/- 19 breaths/min; tidal volume, 167 +/- 21 ml; total ventilation, 52 +/- 9 l/min; effective alveolar ventilation, 5.5 +/- 1.3 l/min; PaO2, 106.2 +/- 5.9 Torr; PaCO2, 27.2 +/- 3.9 Torr; end-tidal-arterial PO2 difference [(PE' - Pa)O2], 26.0 +/- 5.3 Torr; and arterial-end-tidal PCO2 difference, [(Pa - PE')CO2], 14.9 +/- 2.5 Torr. On the basis of the classical ideal alveolar air approach, parallel dead-space ventilation accounted for 54% of alveolar ventilation and 66% of the (PE' - Pa)O2 difference. But the steepness of the CO2 and O2 expirogram plotted against expired volume suggested a contribution of series in homogeneity due to incomplete gas mixing.