Abstract
Enzymes are biological catalysts that are comprised of small-molecule, metal, or cluster catalysts augmented by biopolymeric scaffolds. It is conceivable that early in chemical evolution, ancestral enzymes opted for simpler, easier to assemble scaffolds. Herein, we describe such possible protoenzymes: hyperbranched polymer-scaffolded metal-sulfide nanocrystals. Hyperbranched polyethyleneimine (HyPEI) and glycerol citrate polymer-supported ZnS nanocrystals (NCs) are formed in a simple process. Transmission electron microscopy (TEM) analyses of HyPEI-supported NCs reveal spherical particles with an average size of 10 nm that undergo only a modest aggregation over a 14-day incubation. The polymer-supported ZnS NCs are shown to possess a high photocatalytic activity in an eosin B photodegradation assay, making them an attractive model for the study of the origin of life under the “Zn world” theory dominated by a photocatalytic proto-metabolic redox reaction network. The catalyst, however, could be easily adapted to apply broadly to different protoenzymatic systems.
Highlights
Metabolism is one of the defining characteristics of life
We have investigated the potential of metal-sulfide nanocrystals (NCs) as possible to metal sulfide extend clusters the catalytic assumptions, the role geochemical formation of long-lived
Synthesis of Hyperbranched Polyethyleneimine (HyPEI)-Supported zinc sulfide (ZnS) Nanocrystals (NCs) was adapted from a protocol described by Hassan and Ali [51]
Summary
Metabolism is one of the defining characteristics of life. The primary purpose of metabolism is the efficient utilization of external sources of energy to fuel cellular processes, such as growth and replication [1]. Highly selective and efficient biocatalysts, govern metabolism. Enzymes offer a selective advantage to some reactions by enhancing their rate up to 1023 -fold [2,3], unmatched by other types of catalysts, effectively shaping metabolic transformations. This level of control and order sets metabolism apart from any other set of chemical reactions. The crucial role of enzymes in life has prompted some to argue that catalytic enzyme precursors, or protoenzymes, played a critical role in the emergence of life [4,5]
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