World Library  
Flag as Inappropriate
Email this Article


Article Id: WHEBN0002852057
Reproduction Date:

Title: Allophycocyanin  
Author: World Heritage Encyclopedia
Language: English
Subject: Fluorophore, Lanthanide, Photosynthetic pigments, Cyanobacteria, Red algae
Collection: Cyanobacteria, Photosynthetic Pigments, Red Algae
Publisher: World Heritage Encyclopedia


Allophycocyanin (from Greek: ἄλλος (allos) meaning "other", φύκος (phykos) meaning “alga”, and κυανός (kyanos) meaning "blue") is a protein from the light-harvesting phycobiliprotein family, along with phycocyanin, phycoerythrin and phycoerythrocyanin. It is an accessory pigment to chlorophyll. All phycobiliproteins are water-soluble and therefore cannot exist within the membrane like carotenoids, but aggregate forming clusters that adhere to the membrane called phycobilisomes. Allophycocyanin absorbs and emits red light (650 & 660 nm max, respectively), and is readily found in Cyanobacteria (also called blue-green algae), and red algae. Phycobilin pigments have fluorescent properties that are used in immunoassay kits. In flow cytometry, it is often abbreviated APC. To be effectively used in applications such as FACS, High-Throughput Screening (HTS) and microscopy, APC needs to be chemically cross-linked.


  • Structural characteristics 1
  • Spectral characteristics 2
  • Applications 3
  • References 4

Structural characteristics

Allophycocyanin can be isolated from various species of red or blue-green algae, each producing slightly different forms of the molecule. It is composed of two different subunits (α and β) in which each subunit has one phycocyanobilin (PCB) chromophore. The subunit structure for APC has been determined as (αβ)3. The molecular weight of APC is 105,000 Daltons.

Spectral characteristics

Absorption maximum 652 nm
Additional Absorption peak 625 nm
Emission maximum 657.5 nm
Stokes Shift 5.5 nm
Extinction Coefficient 700,000 M−1cm−1
Quantum Yield 0.68
Brightness 1.6 x 105 M−1cm−1

Cross-linked APC

As mentioned above, in order for APC to be useful in immunoassays it must first be chemically cross-linked to prevent it from dissociating into its component subunits when in common physiological buffers.[1] The conventional method for accomplishing this is through a destructive process wherein the treated APC trimer is chemically disrupted in 8M urea and then allowed to re-associate through in a physiological buffer.[2] An alternative method can be used which preserves the structural integrity of the APC trimer and allows for a brighter, more stable end-product.[3]


Many applications and instruments were developed specifically for Allophycocyanin. It is commonly used in immunoassays such as FACS, flow cytometry, and High Throughput Screening as an acceptor for Europium via Time Resolved-Fluorescence Resonance Energy Transfer (TR-FRET) assays.


  1. ^ George C. Papageorgiou, Thoula Lagoyanni. Effects of chaotropic electrolytes on the structure and electronic excitation coupling of glutaraldehyde- and diimido ester-cross-linked phycobilisomes. Biochimica et Biophysica Acta (BBA) - Bioenergetics Volume 724, Issue 3, 30 September 1983, Pages 323–332
  2. ^ Yeh SW, Ong LJ, Clark JH, Glazer AN. Fluorescence properties of allophycocyanin and a crosslinked allophycocyanin trimer. Cytometry. 1987 Jan; 8(1):91-5.
  3. ^ United States Patent 7256050; High fluorescent intensity cross-linked allophycocyanin. Assigned to Columbia Biosciences Corp.

This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from Hawaii eBook Library are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.