Arginine kinase (AK) is an important regulation factor of energy metabolism in invertebrate. An arginine kinase gene, named HaAK, was identified to be differentially expressed between Cry1Ac-susceptible (96S) and Cry1Ac-resistant (Bt-R) Helicoverpa armigera larvae using cDNA-amplification fragment length polymorphism analysis. The full-length open reading frame sequence of HaAK gene with 1068 bp was isolated from H. armigera. Quantitative reverse transcription polymerase chain reaction assay revealed that HaAK gene is specifically expressed in multiple tissues and at larval developmental stages. The peak expression level of HaAK was detected in the midgut of the fifth-instar larvae. Moreover, the expression of HaAK was obviously down-regulated in Bt-R larvae. We further constructed a dsRNA vector directly targeting HaAK and employed RNAi technology to control the larvae. The feeding bioassays showed that minute quantities of dsRNA could greatly increase the larval mortality and delay the larval pupation. Silencing of HaAK significantly retarded the larval development, indicating that HaAK is a potential target for RNA interference-based pest management.

Phosphoarginine is a cell energy buffer molecule synthesized by the enzyme arginine kinase. In Trypanosoma cruzi, the aetiological agent of Chagas' disease, 2 different isoforms were identified by data mining, but only 1 was expressed during the parasite life cycle. The digitonin extraction pattern of arginine kinase differed from those obtained for reservosomes, glycosomes and mitochondrial markers, and similar to the cytosolic marker. Immunofluorescence analysis revealed that although arginine kinase is localized mainly in unknown punctuated structures and also in the cytosol, it did not co-localize with any of the subcelular markers. This punctuated pattern has previously been observed in many cytosolic proteins of trypanosomatids. The knowledge of the subcellular localization of phosphagen kinases is a crucial issue to understand their physiological role in protozoan parasites.