Observations on Enhancement & Inhibition by Light of Triphosphopyridine Nucleotide Photoreduction in Preparations of Laurencia obtusa (Hudson) Lam.

The alga, Laturencia obtutsa (Hudson) Lam., was collected between 7 and 8 AM from an off-shore reef (Cayo Enrique) at La Parguera, Puerto Rico. All plants came from one location on the reef at ca. one foot depth. They were stored in open-sea water under daylight, and used within 6 hours of harvest. Terminal fronds of similar coloration from the same clump w-ere taken for each experiment. Several grams of the alga were ground with sand for 2 minutes in a chilled mortar and dispersed in twice the algal weight of tris-saline buffer (tris(hydroxymethyl) aminomethane, 0.02 M, pH 7.5, containing 0.35 M NaCl) (19). The brei was passed through 100 mesh nylon cloth and centrifuged one minute at 200 X g. The supernatant layer was used immediately as the plastid suspension. Reaction mixtures contained: tris, pH 7.8, 80 jmoles; MgCl,, 4 /Lmoles; KH2PO4-K,HPO4, pH 7.8, 4 /Amoles; ADP, 2 umoles; TPN, 1.5 ,Amoles; 0.2 ml of the plastid preparation and water to make a total volume of 3.0 ml. [The addition of either 0.01, 0.1, or 0.5 unit photosynthetic pyridine nucleotide reductase, prepared according to San Pietro (15) had no effect