Two forms of chlorophyll a in vivo with distinct photochemical functions.

Action spectra of the Emerson effect in Chlorella and Navicula reveal peaks at 670 mut, in addition to those at 650 mu (Chlorella) and 630 mmicro (Navicula) attributable to chlorophylls b and c. Thus, excitation of chlorophyll a form "chlorophyll a 670" can supplement, in these algae, the excitation of the form "chlorophyll a 680-700." The effect of the auxiliary pigments in these algae may be mediated by energy transfer to "chlorophyll a 670."