Combining with gamma-aminobutyric acid (GABA, 4-aminobutyrate), an amino acid which acts as a neurotransmitter in some organisms, to initiate a change in cell activity.

Catalysis of the reaction: dopamine(out) + Na+(out) = dopamine(in) + Na+(in).

Interacting selectively with a peroxisomal targeting sequence, any of several sequences of amino acids within a protein that can act as a signal for the localization of the protein into the peroxisome.

Interacting selectively with retinal, one of the forms of vitamin A. Retinal plays an important role in the visual process in most vertebrates, combining with opsins to form visual pigments in the retina.

Catalysis of the hydrolysis of polypeptides, preferably at the first bond of Xaa-Arg-Lys, and less commonly at the first bond of Arg-Arg-Xaa, in which Xaa is not Arg or Lys.

The formation from simpler components of tetrahydrobiopterin, the reduced form of biopterin (2-amino-4-hydroxy-6-(1,2-dihydroxypropyl)-pteridine). It functions as a hydroxylation coenzyme, e.g. in the conversion of phenylalanine to tyrosine.

Catalysis of the reaction: gamma-aminobutyric acid(out) + Na+(out) = gamma-aminobutyric acid(in) + Na+(in).

[3-methyl-2-oxobutanoate dehydrogenase (lipoamide)] kinase activity

Catalysis of the reaction: [3-methyl-2-oxobutanoate dehydrogenase (lipoamide)] + ATP = [3-methyl-2-oxobutanoate dehydrogenase (lipoamide)] phosphate + ADP.

Catalysis of the reaction: serotonin(out) + Na+(out) = serotonin(in) + Na+(in).

Enables the directed movement of a nucleoside, a nucleobase linked to either beta-D-ribofuranose (ribonucleoside) or 2-deoxy-beta-D-ribofuranose, (a deoxyribonucleotide), into, out of, within or between cells.

Enables the directed movement of nucleotide-sugars into, out of, within or between cells. A nucleotide-sugars is any nucleotide in which the distal phosphoric residue of a nucleoside 5'-diphosphate is in glycosidic linkage with a monosaccharide or monosaccharide derivative.

Catalysis of the reaction: (S)-2,3-epoxysqualene = lanosterol. This is a cyclization reaction that forms the sterol nucleus.