Queen Mary: nobody expects the Spanish Inquisition

Misconceptions surrounding the relationship between journal impact factor and citation distribution in veterinary medicine

OBJECTIVE

To define the relationship between journal impact factor (JIF) and citation distribution in veterinary journals. Citation distribution is a summary of the number of citations of individual papers published in a defined period, and JIF is said to represent the mean number of citations received by a paper published in a given journal. JIF is criticized for promoting unimportant differences between journals, exaggerating small differences in journal citation distributions by misrepresenting a skewed citation distribution. The hypothesis was that veterinary journals have a skewed citation distribution and that median citation rates between journals would be smaller than that indicated by JIF.

STUDY DESIGN

Bibliometric study.

ANIMALS

None.

METHODS

A published method was used to generate journal citation reports from a commercial database, with search limits set for document ('article' and 'review') and the 2 year citation window of interest. Citation distributions [median (range)] and cumulative citations were calculated for Veterinary Anaesthesia and Analgesia (Vet Anaesth Analg, 2007-2017), 11 preselected subject- and species-specific and general veterinary journals (2016) and veterinary journals from the top (n = 10) and bottom (n = 10) of the Veterinary Sciences category ranking (2016) with a 10 year publication record.

RESULTS

Citation distributions were right-skewed for all journals, with 15-20% of papers contributing approximately 50% of citations. For Vet Anaesth Analg, the median citation distribution [1 (0-2)] did not change despite JIF ranging from 1.044 to 2.064 between 2007 and 2017. Calculated median citation rates revealed minimal differences between journals, with only three groups identified: bottom (median citation 0), preselected (median citation 1) and top (median citation 2) journals. These groups represent over 100 places in the JIF (0.316-3.148) ranking.

CONCLUSIONS

Ranking veterinary journals according to JIF is misleading, exaggerating differences while concealing minimally different citation distributions.

Iron Sulfur and Molybdenum Cofactor Enzymes Regulate the Drosophila Life Cycle by Controlling Cell Metabolism

Iron sulfur (Fe-S) clusters and the molybdenum cofactor (Moco) are present at enzyme sites, where the active metal facilitates electron transfer. Such enzyme systems are soluble in the mitochondrial matrix, cytosol and nucleus, or embedded in the inner mitochondrial membrane, but virtually absent from the cell secretory pathway. They are of ancient evolutionary origin supporting respiration, DNA replication, transcription, translation, the biosynthesis of steroids, heme, catabolism of purines, hydroxylation of xenobiotics, and cellular sulfur metabolism. Here, Fe-S cluster and Moco biosynthesis in Drosophila melanogaster is reviewed and the multiple biochemical and physiological functions of known Fe-S and Moco enzymes are described. We show that RNA interference of Mocs3 disrupts Moco biosynthesis and the circadian clock. Fe-S-dependent mitochondrial respiration is discussed in the context of germ line and somatic development, stem cell differentiation and aging. The subcellular compartmentalization of the Fe-S and Moco assembly machinery components and their connections to iron sensing mechanisms and intermediary metabolism are emphasized. A biochemically active Fe-S core complex of heterologously expressed fly Nfs1, Isd11, IscU, and human frataxin is presented. Based on the recent demonstration that copper displaces the Fe-S cluster of yeast and human ferredoxin, an explanation for why high dietary copper leads to cytoplasmic iron deficiency in flies is proposed. Another proposal that exosomes contribute to the transport of xanthine dehydrogenase from peripheral tissues to the eye pigment cells is put forward, where the Vps16a subunit of the HOPS complex may have a specialized role in concentrating this enzyme within pigment granules. Finally, we formulate a hypothesis that (i) mitochondrial superoxide mobilizes iron from the Fe-S clusters in aconitase and succinate dehydrogenase; (ii) increased iron transiently displaces manganese on superoxide dismutase, which may function as a mitochondrial iron sensor since it is inactivated by iron; (iii) with the Krebs cycle thus disrupted, citrate is exported to the cytosol for fatty acid synthesis, while succinyl-CoA and the iron are used for heme biosynthesis; (iv) as iron is used for heme biosynthesis its concentration in the matrix drops allowing for manganese to reactivate superoxide dismutase and Fe-S cluster biosynthesis to reestablish the Krebs cycle.