[The light-induced activation of NADP(+)-dependent glyceraldehyde-3-phosphate dehydrogenase : IX. The reaction in isolated chloroplasts]

1. A modification of an aqueous isolation procedure of chloroplasts is described. It results in chloroplast preparations of high purity and good maintenance of structure. 2. The activity of NADP-GPD is increased with the same kinetics by irradiance of isolated spinach chloroplasts as by irradiance of the intact organism. 3. Irradiance causes a decrease in NAD-GPD-activity in the isolated chloroplasts. The change in the turn-over rate (Δ A1 of NADP-GPD-increase: Δ A2 of NAD-GPD-decrease) is 5:1. This ratio is of the same order of magnitude as that obtained earlier by irradiance of whole Lemna gibba (Δ A1 : Δ A2 = 3,5 : 1). Evidence is given that the NAD-GPD in the cytoplasm is not influenced by light.

The immune response to a hybrid protein molecule; specificity of secondary stimulation and of tolerance induction

Upon immunization with LDH-III (subunit composition AABB) rabbits produce anti-A and anti-B antibodies in comparable amounts. These antibodies fit equally well to the hybrid enzyme and to LDH-V (AAAA) or LDH-I (BBBB) respectively, as tested by passive hemagglutination inhibition. No antibodies reacting with both LDH-I and LDH-V were detected. A minority of hybrid-specific antibodies was, however, present in the sera. Animals primed with LDH-III respond regularly to a boosting injection of LDH-V with the production of large amounts of anti-A (but not anti-B) antibodies. A similar injection of LDH-I stimulates (if it has any effect at all) the production of anti-B antibodies only. Stimulation with one of the pure types does not impair a subsequent response to the other. The majority of the animals primed with LDH-III responded not at all or weakly to a boosting injection of LDH-I, though antibodies to LDH-I were present in the sera at the time of stimulation. This effect can hardly be explained on the basis of serological sepcificity. Hyporesponsiveness to LDH-III can be induced by injection of LDH-V into the newborn. Both anti-A and anti-B titers are equally depressed. Within the dose range tested, LDH-I does not exert any tolerogenic action with respect to LDH-III. The carrier property of subunit A is evident in the induction of both immunity and tolerance to LDH-III. The early phase of the immune response to the hybrid enzyme may be carrier-specific, and receptors for the haptenic subunit B may not exist at that stage.