A method for producing a heterologous protein comprising: a. providing a fungal host cell having: 1. a modified Gsh1 protein which has a reduced level of activity relative to the activity of a wild-type Gsh1 protein of an otherwise identical reference fungal host cell, and/or 2. a reduced level of activity of Gsh1 protein relative to the activity of a wild-type Gsh1 protein of an otherwise identical reference fungal host cell, and/or 3. a modified GSH1 gene which has a reduced level of activity relative to the activity of a wild-type GSH1 gene of an otherwise identical reference fungal host cell, and/or 4. a reduced level of expression of GSH1 gene relative to the level of expression of a wild-type GSH1 gene of an otherwise identical reference fungal host cell, and b. culturing the host cell to produce the heterologous protein, wherein (i) the heterologous protein is a plant or animal protein, and/or (ii) the culturing is at a scale of at least 1 liter, and/or (iii) the method further comprises purifying the heterologous protein, and/or (iv) the method further comprises formulating the heterologous protein with a therapeutically acceptable carrier or diluent thereby to produce a therapeutic product suitable for administration to a human or an animal. a. providing a fungal host cell having: 1. a modified Gsh1 protein which has a reduced level of activity relative to the activity of a wild-type Gsh1 protein of an otherwise identical reference fungal host cell, and/or 2. a reduced level of activity of Gsh1 protein relative to the activity of a wild-type Gsh1 protein of an otherwise identical reference fungal host cell, and/or 3. a modified GSH1 gene which has a reduced level of activity relative to the activity of a wild-type GSH1 gene of an otherwise identical reference fungal host cell, and/or 4. a reduced level of expression of GSH1 gene relative to the level of expression of a wild-type GSH1 gene of an otherwise identical reference fungal host cell, and 1. a modified Gsh1 protein which has a reduced level of activity relative to the activity of a wild-type Gsh1 protein of an otherwise identical reference fungal host cell, and/or 2. a reduced level of activity of Gsh1 protein relative to the activity of a wild-type Gsh1 protein of an otherwise identical reference fungal host cell, and/or 3. a modified GSH1 gene which has a reduced level of activity relative to the activity of a wild-type GSH1 gene of an otherwise identical reference fungal host cell, and/or 4. a reduced level of expression of GSH1 gene relative to the level of expression of a wild-type GSH1 gene of an otherwise identical reference fungal host cell, and b. culturing the host cell to produce the heterologous protein, wherein (i) the heterologous protein is a plant or animal protein, and/or (ii) the culturing is at a scale of at least 1 liter, and/or (iii) the method further comprises purifying the heterologous protein, and/or (iv) the method further comprises formulating the heterologous protein with a therapeutically acceptable carrier or diluent thereby to produce a therapeutic product suitable for administration to a human or an animal. (i) the heterologous protein is a plant or animal protein, and/or (ii) the culturing is at a scale of at least 1 liter, and/or (iii) the method further comprises purifying the heterologous protein, and/or (iv) the method further comprises formulating the heterologous protein with a therapeutically acceptable carrier or diluent thereby to produce a therapeutic product suitable for administration to a human or an animal.