Photosystem II (PSII) is embedded in the thylakoid membranes of cyanobacteria and plant chloroplasts. PSII is the component of the photosynthetic apparatus that uses solar energy to split water, producing the oxygen in Earth’s atmosphere. PSII is a multi-subunit protein complex that requires several auxiliary proteins to manage its assembly in the thylakoid membrane which also includes the insertion of chlorophyll into its structure. One of these auxiliary proteins Ycf39 associates with two 5-6 kDa chlorophyll-binding proteins HliC and HliD, forming a complex which is involved in the insertion of chlorophyll into the D1 subunit of PSII. In addition, an earlier study (Chidgey et al. (2014) Plant Cell 26: 1267-79) has shown that these 3 proteins can associate with chlorophyll synthase (ChlG), the enzyme responsible for catalysing the final step of chlorophyll biosynthesis, the attachment of the C20 phytyl group to the Mg-containing tetrapyrrole ring. Using FLAG-tagged ChlG to capture Ycf39 and associated proteins and 15N-labelled artificial protein standards to enable protein quantification, we have characterized the effects of both normal and high illumination, together with an HliC knock-out mutant on the ChlG-Ycf39-HliC/D complex.