The mechanism of the photochemical activity of isolated chloroplasts. I. Effect of temperature

• 1.1. The rate-limiting step in the dark process of the Hill reaction has the same activation energy of 10 kcal. for several varieties of the species Beta vulgaris.
• 2.2. The loss of Hill-reaction reactivity of isolated chloroplast fragments is due to at least two different processes: one, significant at temperatures greater than 30 °C., is first-order and demonstrates the characteristics of thermal denaturation of proteins; another, significant at both low and high temperatures, is second-order and has an activation energy of 8 kcal. Both reactions appear to involve participation of at least one common chloroplast substance.
• 3.3. Some samples of chloroplast fragments prepared under nitrogen rather than air can be activated by incubation to a Hill-reaction reactivity as much as 50% higher than normal.