The effects of the ligands phenol and resorcinol on the crystallization of human insulin have been investigated as a function of pH. Powder diffraction data were used to characterize several distinct polymorphic forms. A previously unknown polymorph with monoclinic symmetry (P2(1)) was identified for both types of ligand with similar characteristics [the unit-cell parameters for the insulin-resorcinol complex were a = 114.0228 (8), b = 335.43 (3), c = 49.211 (6) Å, β = 101.531 (8)°].

A series of bovine insulin samples were obtained as 14 polycrystalline precipitates at room temperature in the pH range 5.0-7.6. High-resolution powder X-ray diffraction data were collected to reveal the T6 hexameric insulin form. Sample homogeneity and reproducibility were verified by additional synchrotron measurements using an area detector. Pawley analyses of the powder patterns displayed pH- and radiation-induced anisotropic lattice modifications. The pronounced anisotropic lattice variations observed for T6 insulin were exploited in a 14-data-set Rietveld refinement to obtain an average crystal structure over the pH range investigated. Only the protein atoms of the known structure with PDB code 2a3g were employed in our starting model. A novel approach for refining protein structures using powder diffraction data is presented. In this approach, each amino acid is represented by a flexible rigid body (FRB). The FRB model requires a significantly smaller number of refinable parameters and restraints than a fully free-atom refinement. A total of 1542 stereochemical restraints were imposed in order to refine the positions of 800 protein atoms, two Zn atoms and 44 water molecules in the asymmetric unit using experimental data in the resolution range 18.2-2.7 Å for all profiles.

RationaleParkinson’s disease (PD) impairs working memory (WM)—the ability to maintain items in memory for short periods of time and manipulate them. There is conflicting evidence on the nature of the deficits caused by the disease, and the potential beneficial and detrimental effects of dopaminergic medication on different WM processes.ObjectivesWe hypothesised that PD impairs both maintenance and manipulation of items in WM and dopaminergic medications improve this in PD patients but impair it in healthy older adults.MethodsWe tested 68 PD patients ON and OFF their dopaminergic medication, 83 healthy age-matched controls, and 30 healthy older adults after placebo and levodopa administration. We used the digit span, a WM test with three components (forwards, backwards, and sequence recall) that differ in the amount of manipulation required. We analysed the maximum spans and the percentage of lists correctly recalled, which probe capacity of WM and the accuracy of the memory processes within this capacity, respectively.ResultsPD patients had lower WM capacity across all three digit span components, but only showed reduced percentage accuracy on the components requiring manipulation (backwards and sequence spans). Dopaminergic medication did not affect performance in PD patients. In healthy older adults, levodopa did not affect capacity, but did impair accuracy on one of the manipulation components (sequence), without affecting the other (backwards).ConclusionsThis suggests that the deficit of maintenance capacity and manipulation accuracy in PD patients is not primarily a dopaminergic one and supports a potential “overdosing” of intact manipulation mechanisms in healthy older adults by levodopa.Electronic supplementary materialThe online version of this article (10.1007/s00213-018-5058-6) contains supplementary material, which is available to authorized users.

Dopamine has been implicated in learning from rewards and punishment, and in the expression of this learning. However, many studies do not fully separate retrieval and decision mechanisms from learning and consolidation. Here, we investigated the effects of levodopa (dopamine precursor) on choice performance (isolated from learning or consolidation). We gave 31 healthy older adults 150 mg of levodopa or placebo (double-blinded, randomised) 1 hour before testing them on stimuli they had learned the value of the previous day. We found that levodopa did not affect the overall accuracy of choices, nor the relative expression of positively or negatively reinforced values. This contradicts several studies and suggests that overall dopamine levels may not play a role in the choice performance for values learned through reinforcement learning in older adults.

Hospital, Bristol, UK, BS10 5NB. +44 (0)1174148186. John.grogan@bristol.ac.uk. 10 11 ACKNOWLEDGEMENTS 12 The authors thank BRACE for the use of their building, all the patients and 13 participants who took part in this research, and the funders (Wellcome [097081/Z/11/Z] and 14 Bristol Research into Alzheimer's and Care of the Elderly charity [BRI17/15]). 15 16 ABSTRACT 17 Rationale 18Parkinson's disease (PD) impairs working memory (WM) -the ability to maintain 19 items in memory for short periods of time and manipulate them. There is conflicting evidence 20 on the nature of the deficits caused by the disease, and the potential beneficial and 21 detrimental effects of dopaminergic medication on different WM processes. 22Objectives 23We hypothesised that PD impairs both maintenance and manipulation of items in WM 24 and dopaminergic medications improve this in PD patients but impair it in healthy older 25 adults. 26Methods 27 We tested 68 PD patients ON and OFF their dopaminergic medication, 83 healthy 28 age-matched controls, and 30 healthy older adults after placebo and levodopa administration. 29We used the digit span, a WM test with three components (forwards, backwards and sequence 30 recall) that differ in the amount of manipulation required. We analysed the maximum spans 31 and the percentage of lists correctly recalled, which probe capacity of WM and the accuracy 32 of the memory processes within this capacity, respectively. 33Results 34 PD patients had lower WM capacity across all three digit span components, but only 35 showed reduced percentage accuracy on the components requiring manipulation (backwards 36 and sequence spans). Dopaminergic medication did not affect performance in PD patients. In 37 healthy older adults, levodopa did not affect capacity, but did impair accuracy on one of the 38 manipulation components (sequence), without affecting the other (backwards). 39 Conclusions 40This suggests a non-dopaminergic deficit of maintenance capacity and manipulation 41 accuracy in PD patients, and a potential "overdosing" of intact manipulation mechanisms in 42 healthy older adults by levodopa. 43