| Sumario: | 1. 1. The effect of light and growing time on chlorophyll, protein content and the activity of porphobilinogenase (PBGase), in Euglena gracilis was studied. 2. 2. It was found that neither protein nor chlorophyll content or PBGase activity were dependent upon the days of growing or the light conditions of growth. 3. 3. Some properties of PBGase were studied. The addition of sodium and magnesium salts to the assay system did not modify enzyme activity. Uroporphyrinogen formation was linear with protein over a wide range of enzyme concentration. 4. 4. When activity was expressed on the basis of the amount of porphyrins formed an optimum pH of 7.4 was obtained but when it was expressed in terms of PBG consumed two pH maxima at 7.0 and 8.5 were observed. 5. 5. Direct plots of velocity against PBG concentration, when activity was measured as PBG consumed, were not hyperbolic; double-reciprocal plots were not linear and Hill plots gave a n value of 2, indicating the existence of positive co-operative effects between two binding sites for PBG per molecule of PBGase. © 1987.
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