Adenosine 5′‐monophosphate (AMP) inhibits muscle fructose 1,6‐bisphosphatase (FBPase) about 44 times stronger than the liver isozyme. The key role in strong AMP binding to muscle isozyme play K20, T177 and Q179. Muscle FBPase which has been mutated towards the liver enzyme (K20E/T177M/Q179C) is inhibited by AMP about 26 times weaker than the wild‐type muscle enzyme, but it binds the fluorescent AMP analogue, 2′,3′‐ O ‐(2,4,6‐trinitrophenyl)adenosine 5′‐monophosphate (TNP‐AMP), similarly to the wild‐type liver enzyme. The reverse mutation of liver FBPase towards the muscle isozyme significantly increases the affinity of the mutant to TNP‐AMP. High affinity to the inhibitor but low sensitivity to AMP of the liver triple mutant suggest differences between the isozymes in the mechanism of allosteric signal transmission.

We have isolated and characterized three adjacent Saccharomyces douglasii genes that share remarkable structural homology (97% amino acid sequence identity) with Saccharomyces cerevisiae ARR1 (ACR1), ARR2 (ACR2) and ARR3 (ACR3) genes involved in arsenical resistance. The ARR2 and ARR3 genes encoding the cytoplasmic arsenate reductase and the plasma membrane arsenite transporter are functionally interchangeable in both yeast species. In contrast, a single copy of S. douglasii ARR1 gene is not sufficient to complement the arsenic hypersensitivity of a S. cerevisiae mutant lacking the transcriptional activator Arr1p. This inability may be related to a deletion of a 35-bp sequence including the putative Yap-binding element in the ARR1 promoter of S. douglasii. Different mechanisms of regulation of ARR1 genes expression may therefore explain the increased tolerance of S. douglasii to arsenic in comparison with S. cerevisiae. The apparent duplication of the ARR gene cluster in the S. douglasii genome may constitute another factor contributing to the observed differences in arsenic sensitivity. Comparison of ARR genes from the genomes of several yeast species indicates that they are located in subtelomeric regions undergoing rapid evolution involving large-scale genomic rearrangements.

Active transport of metalloids by Acr3p and Ycf1p in Saccharomyces cerevisiae and chelation by phytochelatins in Schizosaccharomyces pombe, nematodes, and plants represent distinct strategies of metalloid detoxification. In this report, we present results of functional comparison of both resistance mechanisms. The S. pombe and wheat phytochelatin synthase (PCS) genes, when expressed in S. cerevisiae, mediate only modest resistance to arsenite and thus cannot functionally compensate for Acr3p. On the other hand, we show for the first time that phytochelatins also contribute to antimony tolerance as PCS fully complement antimonite sensitivity of ycf1Δ mutant. Remarkably, heterologous expression of PCS sensitizes S. cerevisiae to arsenate, while ACR3 confers much higher arsenic resistance in pcsΔ than in wild-type S. pombe. The analysis of PCS and ACR3 homologues distribution in various organisms and our experimental data suggest that separation of ACR3 and PCS genes may lead to the optimal tolerance status of the cell.