Where does substrate collide?

The molecule on which an enzyme acts: it binds at the enzyme's active site, where it is held in position and chemically converted into product, and its identity is what a given enzyme is selective for. Koshland's 1958 Application of a Theory of Enzyme Specificity to Protein Synthesis argued that the enzyme changes shape to fit and grip this molecule, the induced-fit account of enzyme and substrate specificity that still frames how the binding is understood. The referent is a reacting molecule consumed at an active site, measured by how fast it is turned into product, and it is not a surface an organism grows on, a wafer a circuit is printed on, or a language that colours another.[1]

Unit

One molecule bound and converted at an enzyme's active site

Recovery means

Not applicable: the molecule is used up as it becomes product, while the enzyme is released unchanged

Measured by

By reaction kinetics, tracking how the amount of substrate sets reaction rate through Michaelis-Menten parameters

The surface or medium on or in which an organism lives, settles, or grows: the bed of a stream, the soil, or the rock or plant that a fixed creature attaches to, described by its particle size, texture, and stability. Cummins and Lauff's 1969 The influence of substrate particle size on the microdistribution of stream macrobenthos showed how the grain size of a stream bed governs which invertebrates live where. The referent is a physical habitat surface characterised by its texture, and it is not a molecule an enzyme converts, a wafer under a circuit, or a language beneath another.[2]

Unit

A patch of habitat surface or medium, described by particle size and texture

Recovery means

Not applicable

Measured by

By particle-size grading, mapping of the bed or soil, and counts of the organisms found on or within it

A language that influences a more dominant language when their speakers are in prolonged contact, leaving traces in the dominant language after a population shifts away from its own tongue: the substrate is the receding or lower-status language, contrasted with the superstrate that prevails. Thomason and Kaufman's 1988 Language Contact, Creolization, and Genetic Linguistics set out how shift-driven interference from a substrate leaves marks in the sound system and grammar of the language that replaces it. The referent is a receding contact language whose influence is read in another language's features, and it is not a molecule at an active site, a habitat surface, or a wafer.[3]

Unit

A source language whose features surface in a dominant language after a shift

Recovery means

Not applicable

Measured by

By comparing features of the resulting language against the substrate and superstrate source languages