Metamorphic zonation and formation granulite in the Shizunai area, the Hidaka Metamorphic Belt, Hokkaido, Japan

The central part of the Hidaka Metamorphic Belt (HMB) is divided into six metamorphic zones : lower-biotite, upper-biotite, garnet, sillimanite-muscovite, garnet-cordierite and orthopyroxene zones. A significant temperature gap with lithological contrast is recognized between the sillimanite-muscovite and garnet-cordierite zones. In the garnet-cordierite and orthopyroxene zones, marked prograde zoning profiles occur in garnets in amphibolites. Geothermometry and diffusion modeling for the zoning profiles of these garnets suggest that the rims were formed under upper amphibolite-facies and granulite-facies conditions, with a brief and rapid increase in temperature at peak metamorphism. The latest pulse of SHRIMP zircon dating of granulite (Early Miocene) in the Hidakahorobetsu River area may explain the granulite-facies metamorphism recorded the garnet rims, which occurred just before the uplift episode indicated by K-Ar ages

The Aminolysis Reaction of Streptomyces S9 Aminopeptidase Promotes the Synthesis of Diverse Prolyl Dipeptides▿ †

Prolyl dipeptide synthesis by S9 aminopeptidase from Streptomyces thermocyaneoviolaceus (S9AP-St) has been demonstrated. In the synthesis, S9AP-St preferentially used l-Pro-OBzl as the acyl donor, yielding synthesized dipeptides having an l-Pro-Xaa structure. In addition, S9AP-St showed broad specificity toward the acyl acceptor. Furthermore, S9AP-St produced cyclo (l-Pro-l-His) with a conversion ratio of substrate to cyclo (l-Pro-l-His) higher than 40%

Dating deformation using sheared leucogranite: temporal constraints by ⁴⁰Ar/³⁹Ar thermochronology for the Mae Ping shear zone, NW Thailand

The Mae Ping shear zone (MPSZ) is one of the major ductile strike-slip systems associated with the Cenozoic extrusion tectonics in Southeast Asia. However, its sinistral shear lacks a robust temporal constraint. This study attempts to acquire the deformation timing by applying 40Ar/39Ar thermochronology on a sheared pegmatitic leucogranite showing sinistral S–C fabrics with a thrust component. The contact of the leucogranite sub-paralleling to the major foliation in host gneiss indicates it could be a pre- to syn-shearing intrusion. Most minerals, including garnet, muscovite, K-feldspar, albite, and quartz, exhibit ductile to brittle deformation. Mineral microstructural analysis suggests a retrograde sinistral shear from > 600 to 250 °C. In situ 40Ar/39Ar dating on muscovite yield ages mainly within 42–38 Ma with calculated closure temperatures of 435–330 °C. Fine-grained muscovite aggregates are slightly older than fish, implying that grain size reduction may not always reset 40Ar/39Ar ages. The K-feldspar 40Ar/39Ar step heating age spectrum with two segments of contiguous steps at 24.5 and 35.4 Ma may reflect the coexistence of high-T porphyroclast and low-T K-rich fine-grain recrystallizing at pressure shadows. The reconstructed cooling path and inferred deformation temperatures constrain a shear duration of 42–30 Ma for the MPSZ. The activation of the MPSZ before 42 Ma could be linked to the Eocene metamorphism within a transpressional regime triggering crustal thickening that may further induce the leucogranitic melt. This study also shows leucogranite can be a nice thermal history recorder for a shear zone regarding its petrogenesis and suitable mineral assemblage for thermochronology

One-Pot Synthesis of Diverse dl-Configuration Dipeptides by a Streptomyces d-Stereospecific Amidohydrolase ▿ †

The synthesis of diverse dl-configuration dipeptides in a one-pot reaction was demonstrated by using a function of the aminolysis reaction of a d-stereospecific amidohydrolase from Streptomyces sp., a clan SE, S12 family peptidase categorized as a peptidase with d-stereospecificity. The enzyme was able to use various aminoacyl derivatives, including l-aminoacyl derivatives, as acyl donors and acceptors. Investigations of the specificity of the peptide synthetic activity revealed that the enzyme preferentially used d-aminoacyl derivatives as acyl donors. In contrast, l-amino acids and their derivatives were preferentially used as acyl acceptors. Consequently, the synthesized dipeptides had a dl-configuration when d- and l-aminoacyl derivatives were mixed in a one-pot reaction. This report also describes that the enzyme produced cyclo(d–Pro-l-Arg), a specific inhibitor of family 18 chitinase, with a conversion rate for d-Pro benzyl ester and l-Arg methyl ester to cyclo(d-Pro–l-Arg) of greater than 65%. Furthermore, based on results of cyclo(d-Pro–l-Arg) synthesis, we propose a reaction mechanism for cyclo(d-Pro–l-Arg) production